EncryptHub Exploits Windows Zero-Day to Deploy Rhadamanthys and StealC Malware
Summary:
The threat actor known as EncryptHub has been exploiting a recently patched zero-day vulnerability in Microsoft Windows, CVE-2025-26633 (CVSS score: 7.0), to deliver various malware families, including Rhadamanthys and StealC, which are commonly used for backdoor access and information stealing. This flaw, which was addressed in Microsoft’s March 2025 Patch Tuesday, is an improper neutralization vulnerability in the Microsoft Management Console that can be leveraged to bypass local security features.
According to Trend Micro researcher Aliakbar Zahravi, EncryptHub abuses the MMC’s Multilingual User Interface Path (MUIPath) and manipulates .msc (Microsoft Console) files to stealthily download and execute malicious payloads, maintain persistence, and extract sensitive user data. Trend Micro has dubbed this technique “MSC EvilTwin”, highlighting how the exploit abuses the way mmc.exe resolves MUIPath to substitute a clean .msc file with a malicious one. This is done by placing two .msc files with identical names in different directories—one legitimate and one malicious placed in an “en-US” subdirectory—so that MMC, when run, loads the malicious version unknowingly. This activity is attributed to a suspected Russian threat cluster, tracked by Trend Micro as Water Gamayun and by others as LARVA-208, which has also been the subject of research by PRODAFT and Outpost24. The MSC EvilTwin loader, a custom PowerShell-based loader, is responsible for deploying the .msc payloads and has been observed experimenting with various delivery and execution techniques.
Security Officer Comments:
Initial infection often begins with victims being tricked into downloading digitally-signed MSI installers that impersonate legitimate Chinese applications such as DingTalk or QQTalk. These MSI files are then used to retrieve and run the malicious loader from attacker-controlled servers. Trend Micro’s analysis indicates that EncryptHub has been actively developing and refining this campaign since at least April 2024, deploying multiple custom payloads to ensure persistence and covert data exfiltration to its command-and-control (C2) infrastructure. Overall, this campaign showcases advanced abuse of Windows internals and file resolution logic, emphasizing the need for organizations to apply patches promptly and monitor for unusual MMC activity and suspicious .msc file behavior.
Suggested Corrections:
Backup your data, system images, and configurations, regularly test them, and keep the backups offline: Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.
Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to drive your patch management program.
Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?
Check your security team's work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.
Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks, and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety-critical functions can be maintained during a cyber incident.
Train employees: Email remains the most vulnerable attack vector for organizations. Users should be trained on how to avoid and spot phishing emails. Multi-factor authentication can help prevent malicious access to sensitive services.
Implement multi-factor authentication (MFA): External-facing assets that leverage single-factor authentication (SFA) are highly susceptible to brute-forcing attacks, password spraying, or unauthorized remote access using valid (stolen) credentials. Implementing MFA enhances security and adds an extra layer of protection.
Link(s):
https://thehackernews.com/2025/03/encrypthub-exploits-windows-zero-day-to.html
The threat actor known as EncryptHub has been exploiting a recently patched zero-day vulnerability in Microsoft Windows, CVE-2025-26633 (CVSS score: 7.0), to deliver various malware families, including Rhadamanthys and StealC, which are commonly used for backdoor access and information stealing. This flaw, which was addressed in Microsoft’s March 2025 Patch Tuesday, is an improper neutralization vulnerability in the Microsoft Management Console that can be leveraged to bypass local security features.
According to Trend Micro researcher Aliakbar Zahravi, EncryptHub abuses the MMC’s Multilingual User Interface Path (MUIPath) and manipulates .msc (Microsoft Console) files to stealthily download and execute malicious payloads, maintain persistence, and extract sensitive user data. Trend Micro has dubbed this technique “MSC EvilTwin”, highlighting how the exploit abuses the way mmc.exe resolves MUIPath to substitute a clean .msc file with a malicious one. This is done by placing two .msc files with identical names in different directories—one legitimate and one malicious placed in an “en-US” subdirectory—so that MMC, when run, loads the malicious version unknowingly. This activity is attributed to a suspected Russian threat cluster, tracked by Trend Micro as Water Gamayun and by others as LARVA-208, which has also been the subject of research by PRODAFT and Outpost24. The MSC EvilTwin loader, a custom PowerShell-based loader, is responsible for deploying the .msc payloads and has been observed experimenting with various delivery and execution techniques.
Security Officer Comments:
Initial infection often begins with victims being tricked into downloading digitally-signed MSI installers that impersonate legitimate Chinese applications such as DingTalk or QQTalk. These MSI files are then used to retrieve and run the malicious loader from attacker-controlled servers. Trend Micro’s analysis indicates that EncryptHub has been actively developing and refining this campaign since at least April 2024, deploying multiple custom payloads to ensure persistence and covert data exfiltration to its command-and-control (C2) infrastructure. Overall, this campaign showcases advanced abuse of Windows internals and file resolution logic, emphasizing the need for organizations to apply patches promptly and monitor for unusual MMC activity and suspicious .msc file behavior.
Suggested Corrections:
Backup your data, system images, and configurations, regularly test them, and keep the backups offline: Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.
Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to drive your patch management program.
Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?
Check your security team's work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.
Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks, and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety-critical functions can be maintained during a cyber incident.
Train employees: Email remains the most vulnerable attack vector for organizations. Users should be trained on how to avoid and spot phishing emails. Multi-factor authentication can help prevent malicious access to sensitive services.
Implement multi-factor authentication (MFA): External-facing assets that leverage single-factor authentication (SFA) are highly susceptible to brute-forcing attacks, password spraying, or unauthorized remote access using valid (stolen) credentials. Implementing MFA enhances security and adds an extra layer of protection.
Link(s):
https://thehackernews.com/2025/03/encrypthub-exploits-windows-zero-day-to.html