A convincing lookalike of the popular 7-Zip archiver site has been serving a trojanized installer that silently converts victims’ machines into residential proxy nodes—and it has been hiding in plain sight for some time.

“I’m so sick to my stomach”

A PC builder recently turned to Reddit’s r/pcmasterrace community in a panic after realizing they had downloaded 7‑Zip from the wrong website. Following a YouTube tutorial for a new build, they were instructed to download 7‑Zip from 7zip[.]com, unaware that the legitimate project is hosted exclusively at 7-zip.org.

In their Reddit post, the user described installing the file first on a laptop and later transferring it via USB to a newly built desktop. They encountered repeated 32‑bit versus 64‑bit errors and ultimately abandoned the installer in favor of Windows’ built‑in extraction tools. Nearly two weeks later, Microsoft Defender alerted on the system with a generic detection: Trojan:Win32/Malgent!MSR.

The experience illustrates how a seemingly minor domain mix-up can result in long-lived, unauthorized use of a system when attackers successfully masquerade as trusted software distributors.

A trojanized installer masquerading as legitimate software

This is not a simple case of a malicious download hosted on a random site. The operators behind 7zip[.]com distributed a trojanized installer via a lookalike domain, delivering a functional copy of functional 7‑Zip File Manager alongside a concealed malware payload.

The installer is Authenticode‑signed using a now‑revoked certificate issued to Jozeal Network Technology Co., Limited, lending it superficial legitimacy. During installation, a modified build of 7zfm.exe is deployed and functions as expected, reducing user suspicion. In parallel, three additional components are silently dropped:

• Uphero.exe—a service manager and update loader
• hero.exe—the primary proxy payload (Go‑compiled)
• hero.dll—a supporting library

All components are written to C:\Windows\SysWOW64\hero\, a privileged directory that is unlikely to be manually inspected.

An independent update channel was also observed at update.7zip[.]com/version/win-service/1.0.0.2/Uphero.exe.zip, indicating that the malware payload can be updated independently of the installer itself.

Abuse of trusted distribution channels

One of the more concerning aspects of this campaign is its reliance on third‑party trust. The Reddit case highlights YouTube tutorials as an inadvertent malware distribution vector, where creators incorrectly reference 7zip.com instead of the legitimate domain.

This shows how attackers can exploit small errors in otherwise benign content ecosystems to funnel victims toward malicious infrastructure at scale.

Execution flow: from installer to persistent proxy service

Behavioral analysis shows a rapid and methodical infection chain:

1. File deployment—The payload is installed into SysWOW64, requiring elevated privileges and signaling intent for deep system integration.

2. Persistence via Windows services—Both Uphero.exe and hero.exe are registered as auto‑start Windows services running under System privileges, ensuring execution on every boot.

3. Firewall rule manipulation—The malware invokes netsh to remove existing rules and create new inbound and outbound allow rules for its binaries. This is intended to reduce interference with network traffic and support seamless payload updates.

4. Host profiling—Using WMI and native Windows APIs, the malware enumerates system characteristics including hardware identifiers, memory size, CPU count, disk attributes, and network configuration. The malware communicates with iplogger[.]org via a dedicated reporting endpoint, suggesting it collects and reports device or network metadata as part of its proxy infrastructure.

Functional goal: residential proxy monetization

While initial indicators suggested backdoor‑style capabilities, further analysis revealed that the malware’s primary function is proxyware. The infected host is enrolled as a residential proxy node, allowing third parties to route traffic through the victim’s IP address.

The hero.exe component retrieves configuration data from rotating “smshero”‑themed command‑and‑control domains, then establishes outbound proxy connections on non‑standard ports such as 1000 and 1002. Traffic analysis shows a lightweight XOR‑encoded protocol (key 0x70) used to obscure control messages.

This infrastructure is consistent with known residential proxy services, where access to real consumer IP addresses is sold for fraud, scraping, ad abuse, or anonymity laundering.

Shared tooling across multiple fake installers

The 7‑Zip impersonation appears to be part of a broader operation. Related binaries have been identified under names such as upHola.exe, upTiktok, upWhatsapp, and upWire, all sharing identical tactics, techniques, and procedures:

• Deployment to SysWOW64
• Windows service persistence
• Firewall rule manipulation via netsh
• Encrypted HTTPS C2 traffic

Embedded strings referencing VPN and proxy brands suggest a unified backend supporting multiple distribution fronts.

Rotating infrastructure and encrypted transport

Memory analysis uncovered a large pool of hardcoded command-and-control domains using hero and smshero naming conventions. Active resolution during sandbox execution showed traffic routed through Cloudflare infrastructure with TLS‑encrypted HTTPS sessions.

The malware also uses DNS-over-HTTPS via Google’s resolver, reducing visibility for traditional DNS monitoring and complicating network-based detection.

Evasion and anti‑analysis features

The malware incorporates multiple layers of sandbox and analysis evasion:

• Virtual machine detection targeting VMware, VirtualBox, QEMU, and Parallels
• Anti‑debugging checks and suspicious debugger DLL loading
• Runtime API resolution and PEB inspection
• Process enumeration, registry probing, and environment inspection

Cryptographic support is extensive, including AES, RC4, Camellia, Chaskey, XOR encoding, and Base64, suggesting encrypted configuration handling and traffic protection.

Defensive guidance

Any system that has executed installers from 7zip.com should be considered compromised. While this malware establishes SYSTEM‑level persistence and modifies firewall rules, reputable security software can effectively detect and remove the malicious components. Malwarebytes is capable of fully eradicating known variants of this threat and reversing its persistence mechanisms. In high‑risk or heavily used systems, some users may still choose a full OS reinstall for absolute assurance, but it is not strictly required in all cases.

Users and defenders should:

• Verify software sources and bookmark official project domains
• Treat unexpected code‑signing identities with skepticism
• Monitor for unauthorized Windows services and firewall rule changes
• Block known C2 domains and proxy endpoints at the network perimeter

Researcher attribution and community analysis

This investigation would not have been possible without the work of independent security researchers who went deeper than surface-level indicators and identified the true purpose of this malware family.

• Luke Acha provided the first comprehensive analysis showing that the Uphero/hero malware functions as residential proxyware rather than a traditional backdoor. His work documented the proxy protocol, traffic patterns, and monetization model, and connected this campaign to a broader operation he dubbed upStage Proxy. Luke’s full write-up is available on his blog.
• s1dhy expanded on this analysis by reversing and decoding the custom XOR-based communication protocol, validating the proxy behavior through packet captures, and correlating multiple proxy endpoints across victim geolocations. Technical notes and findings were shared publicly on X (Twitter).
• Andrew Danis contributed additional infrastructure analysis and clustering, helping tie the fake 7-Zip installer to related proxyware campaigns abusing other software brands.

Additional technical validation and dynamic analysis were published by researchers at RaichuLab on Qiita and WizSafe Security on IIJ.

Their collective work highlights the importance of open, community-driven research in uncovering long-running abuse campaigns that rely on trust and misdirection rather than exploits.

Closing thoughts

This campaign demonstrates how effective brand impersonation combined with technically competent malware can operate undetected for extended periods. By abusing user trust rather than exploiting software vulnerabilities, attackers bypass many traditional security assumptions—turning everyday utility downloads into long‑lived monetization infrastructure.

Malwarebytes detects and blocks known variants of this proxyware family and its associated infrastructure.

Indicators of Compromise (IOCs)

File paths

• C:\Windows\SysWOW64\hero\Uphero.exe
• C:\Windows\SysWOW64\hero\hero.exe
• C:\Windows\SysWOW64\hero\hero.dll

File hashes (SHA-256)

• e7291095de78484039fdc82106d191bf41b7469811c4e31b4228227911d25027 (Uphero.exe)
• b7a7013b951c3cea178ece3363e3dd06626b9b98ee27ebfd7c161d0bbcfbd894 (hero.exe)
• 3544ffefb2a38bf4faf6181aa4374f4c186d3c2a7b9b059244b65dce8d5688d9 (hero.dll)

Network indicators

Domains:

• soc.hero-sms[.]co
• neo.herosms[.]co
• flux.smshero[.]co
• nova.smshero[.]ai
• apex.herosms[.]ai
• spark.herosms[.]io
• zest.hero-sms[.]ai
• prime.herosms[.]vip
• vivid.smshero[.]vip
• mint.smshero[.]com
• pulse.herosms[.]cc
• glide.smshero[.]cc
• svc.ha-teams.office[.]com
• iplogger[.]org

Observed IPs (Cloudflare-fronted):

• 104.21.57.71
• 172.67.160.241

Host-based indicators

• Windows services with image paths pointing to C:\Windows\SysWOW64\hero\
• Firewall rules named Uphero or hero (inbound and outbound)
• Mutex: Global\3a886eb8-fe40-4d0a-b78b-9e0bcb683fb7

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Stay safe!

The Microsoft Defender Research Team observed a multi‑stage intrusion where threat actors exploited internet‑exposed SolarWinds Web Help Desk (WHD) instances to get an initial foothold and then laterally moved towards other high-value assets within the organization. However, we have not yet confirmed whether the attacks are related to the most recent set of WHD vulnerabilities disclosed on January 28, 2026, such as CVE-2025-40551 and CVE-2025-40536 or stem from previously disclosed vulnerabilities like CVE-2025-26399. Since the attacks occurred in December 2025 and on machines vulnerable to both the old and new set of CVEs at the same time, we cannot reliably confirm the exact CVE used to gain an initial foothold.

This activity reflects a common but high-impact pattern: a single exposed application can provide a path to full domain compromise when vulnerabilities are unpatched or insufficiently monitored. In this intrusion, attackers relied heavily on living-off-the-land techniques, legitimate administrative tools, and low-noise persistence mechanisms. These tradecraft choices reinforce the importance of Defense in Depth, timely patching of internet-facing services, and behavior-based detection across identity, endpoint, and network layers.

In this post, the Microsoft Defender Research Team shares initial observations from the investigation, along with detection and hunting guidance and security posture hardening recommendations to help organizations reduce exposure to this threat. Analysis is ongoing, and this post will be updated as additional details become available.

Technical details

The Microsoft Defender Research Team identified active, in-the-wild exploitation of exposed SolarWinds Web Help Desk (WHD). Further investigations are in-progress to confirm the actual vulnerabilities exploited, such as CVE-2025-40551 (critical untrusted data deserialization) and CVE-2025-40536 (security control bypass) and CVE-2025-26399. Successful exploitation allowed the attackers to achieve unauthenticated remote code execution on internet-facing deployments, allowing an external attacker to execute arbitrary commands within the WHD application context.

Upon successful exploitation, the compromised service of a WHD instance spawned PowerShell to leverage BITS for payload download and execution:

On several hosts, the downloaded binary installed components of the Zoho ManageEngine, a legitimate remote monitoring and management (RMM) solution, providing the attacker with interactive control over the compromised system. The attackers then enumerated sensitive domain users and groups, including Domain Admins. For persistence, the attackers established reverse SSH and RDP access. In some environments, Microsoft Defender also observed and raised alerts flagging attacker behavior on creating a scheduled task to launch a QEMU virtual machine under the SYSTEM account at startup, effectively hiding malicious activity within a virtualized environment while exposing SSH access via port forwarding.

SCHTASKS /CREATE /V1 /RU SYSTEM /SC ONSTART /F /TN "TPMProfiler" /TR 		"C:\Users\\tmp\qemu-system-x86_64.exe -m 1G -smp 1 -hda vault.db -		device e1000,netdev=net0 -netdev user,id=net0,hostfwd=tcp::22022-:22"

On some hosts, threat actors used DLL sideloading by abusing wab.exe to load a malicious sspicli.dll. The approach enables access to LSASS memory and credential theft, which can reduce detections that focus on well‑known dumping tools or direct‑handle patterns. In at least one case, activity escalated to DCSync from the original access host, indicating use of high‑privilege credentials to request password data from a domain controller. In ne next figure we highlight the attack path.

Mitigation and protection guidance

• Patch and restrict exposure now. Update WHD CVE-2025-40551, CVE-2025-40536 and CVE-2025-26399, remove public access to admin paths, and increase logging on Ajax Proxy.
• Evict unauthorized RMM. Find and remove ManageEngine RMM artifacts (for example, ToolsIQ.exe) added after exploitation.
• Reset and isolate. Rotate credentials (start with service and admin accounts reachable from WHD), and isolate compromised hosts.

Microsoft Defender XDR detections 

Microsoft Defender provides pre-breach and post-breach coverage for this campaign. Customers can rapidly identify vulnerable but unpatched WHD instances at risk using MDVM capabilities for the CVE referenced above and review the generic and specific alerts suggested below providing coverage of attacks across devices and identity.

Microsoft Defender XDR Hunting queries   

Security teams can use the advanced hunting capabilities in Microsoft Defender XDR to proactively look for indicators of exploitation.

The following Kusto Query Language (KQL) query can be used to identify devices that are using the vulnerable software:

1) Find potential post-exploitation execution of suspicious commands

DeviceProcessEvents 
| where InitiatingProcessParentFileName endswith "wrapper.exe" 
| where InitiatingProcessFolderPath has \\WebHelpDesk\\bin\\ 
| where InitiatingProcessFileName  in~ ("java.exe", "javaw.exe") or InitiatingProcessFileName contains "tomcat" 
| where FileName  !in ("java.exe", "pg_dump.exe", "reg.exe", "conhost.exe", "WerFault.exe") 
 
 
let command_list = pack_array("whoami", "net user", "net group", "nslookup", "certutil", "echo", "curl", "quser", "hostname", "iwr", "irm", "iex", "Invoke-Expression", "Invoke-RestMethod", "Invoke-WebRequest", "tasklist", "systeminfo", "nltest", "base64", "-Enc", "bitsadmin", "expand", "sc.exe", "netsh", "arp ", "adexplorer", "wmic", "netstat", "-EncodedCommand", "Start-Process", "wget"); 
let ImpactedDevices =  
DeviceProcessEvents 
| where isnotempty(DeviceId) 
| where InitiatingProcessFolderPath has "\\WebHelpDesk\\bin\\" 
| where ProcessCommandLine has_any (command_list) 
| distinct DeviceId; 
DeviceProcessEvents 
| where DeviceId in (ImpactedDevices | distinct DeviceId) 
| where InitiatingProcessParentFileName has "ToolsIQ.exe" 
| where FileName != "conhost.exe"

2) Find potential ntds.dit theft

DeviceProcessEvents
| where FileName =~ "print.exe"
| where ProcessCommandLine has_all ("print", "/D:", @"\windows\ntds\ntds.dit")

3) Identify vulnerable SolarWinds WHD Servers

 DeviceTvmSoftwareVulnerabilities 
| where CveId has_any ('CVE-2025-40551', 'CVE-2025-40536', 'CVE-2025-26399')

References

• CVE-2025-40551: SolarWinds Web Help Desk RCE | Horizon3.ai
• NVD – CVE-2025-40551
• SolarWinds Trust Center Security Advisories | CVE-2025-40551
• NVD – CVE-2025-40536
• SolarWinds Trust Center Security Advisories | CVE-2025-40536
• NVD – CVE-2025-26399SolarWinds Trust Center Security Advisories | CVE-2025-26399
• WHD 2026.1 release notes
• Known Exploited Vulnerabilities Catalog | CISA

This research is provided by Microsoft Defender Security Research with contributions from Sagar Patil, Hardik Suri, Eric Hopper, and Kajhon Soyini.

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The post Analysis of active exploitation of SolarWinds Web Help Desk appeared first on Microsoft Security Blog.

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The post Novel Technique to Detect Cloud Threat Actor Operations appeared first on Unit 42.