Executive Summary

CVE-2019-25741 is a structured exception handling (SEH) based buffer overflow vulnerability found in Mobatek MobaXterm version 12.1 and earlier. It occurs in the username field of session files. An attacker can craft a malicious MobaXterm sessions file containing overflow data that triggers this vulnerability when imported and executed by the user.

This vulnerability allows remote attackers to execute arbitrary code on the affected system. Specifically, it enables the execution of a reverse shell with the same privileges as the user running MobaXterm. The exploit involves overflowing the buffer in the username field, overwriting SEH structures, and injecting shellcode that connects back to the attacker.

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Compliance Impact

The provided information does not specify how the CVE-2019-25741 vulnerability in Mobatek MobaXterm affects compliance with common standards and regulations such as GDPR or HIPAA.

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Impact Analysis

This vulnerability can have severe impacts including unauthorized remote code execution on your system. An attacker who successfully exploits this flaw can gain a reverse shell with user-level privileges, effectively allowing them to control your system remotely.

• Execution of arbitrary commands on the affected system.
• Potential theft of sensitive information.
• Unauthorized access and control over the compromised machine.
• Bypassing security controls due to improper input validation.

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Detection Guidance

This vulnerability can be detected by monitoring for the import and execution of suspicious or malicious MobaXterm session files, especially those containing unusually large or crafted username fields that may trigger the buffer overflow.

Since the exploit involves importing a specially crafted session file, detection can focus on identifying such files before they are opened.

On the system, you can check for the presence of suspicious session files with unusually large username fields or unexpected modifications in the MobaXterm sessions directory.

Network detection can involve monitoring for reverse shell connections initiated by MobaXterm processes, which may indicate exploitation.

Suggested commands to help detect exploitation attempts include:

• On Windows, use PowerShell or command prompt to list recent session files: `dir %USERPROFILE%\Documents\MobaXterm\sessions`
• Use a tool like `strings` or a hex editor to inspect session files for abnormally large or suspicious username fields.
• Monitor network connections for unusual outbound connections from MobaXterm processes, e.g., using `netstat -ano | findstr <MobaXterm PID>` or Windows Resource Monitor.
• Use Windows Event Logs or Sysmon to detect process creation events related to MobaXterm and any spawned reverse shell connections.

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Mitigation Strategies

Immediate mitigation steps include:

• Avoid importing or opening untrusted or unknown MobaXterm session files, especially those received from unverified sources.
• Update MobaXterm to a version later than 12.1 where this vulnerability is fixed, if such an update is available.
• Restrict user permissions to prevent unauthorized creation or modification of session files.
• Implement network-level controls to block unexpected outbound connections that could be used for reverse shells.
• Educate users about the risks of opening suspicious session files and encourage verification of file sources.

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