Executive Summary

CVE-2019-25607 is a local stack-based buffer overflow vulnerability in Axessh version 4.2. It occurs in the log file name field, where supplying an excessively long filename causes a buffer overflow at an offset of 214 bytes. This overflow allows a local attacker to overwrite the instruction pointer and execute arbitrary shellcode with system-level privileges.

The vulnerability is classified under CWE-787 (Out-of-bounds Write) and has a high severity score (CVSS v4 base score of 8.6). Exploiting this flaw enables attackers to gain elevated code execution capabilities on affected systems.

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Impact Analysis

This vulnerability allows a local attacker to execute arbitrary code with system privileges by overflowing a buffer in the log file name field. As a result, an attacker can gain full control over the affected system, potentially installing malware, stealing sensitive data, or disrupting system operations.

The exploit can lead to a complete compromise of confidentiality, integrity, and availability of the system, as attackers can run shellcode that may spawn persistent remote shells or execute malicious payloads.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability is a local stack-based buffer overflow in Axessh 4.2 triggered by supplying an excessively long filename in the log file name field. Detection involves checking if the application is vulnerable by attempting to reproduce the overflow condition locally.'}, {'type': 'paragraph', 'content': "One practical detection method is to input a long string (e.g., 500 characters) into the 'Log file name' field in the application's logging settings and observe if the application crashes or behaves abnormally, indicating a buffer overflow."}, {'type': 'paragraph', 'content': 'Commands or steps to detect the vulnerability include:'}, {'type': 'list_item', 'content': 'Create a payload of 500 \'A\' characters (e.g., using Python: `python -c "print(\'\\x41\' * 500)" > Axess.txt`).'}, {'type': 'list_item', 'content': 'Copy the contents of the payload file to the clipboard.'}, {'type': 'list_item', 'content': 'Launch Axessh.exe on a Windows 7 SP1 x86 system.'}, {'type': 'list_item', 'content': "Navigate to 'Telnet Connect Host' -> 'Details>>' -> 'Settings' -> 'Logging' tab."}, {'type': 'list_item', 'content': "Enable 'Log all sessions output' and paste the long string into the 'Log file name' field."}, {'type': 'list_item', 'content': 'Confirm and attempt to connect; if the application crashes, the vulnerability is present.'}] [4]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'Immediate mitigation steps include preventing local attackers from supplying excessively long filenames in the log file name field of Axessh 4.2.'}, {'type': 'paragraph', 'content': 'Since the vulnerability requires local access, restricting user permissions and limiting access to the affected system can reduce risk.'}, {'type': 'paragraph', 'content': 'Additional steps include:'}, {'type': 'list_item', 'content': 'Avoid using Axessh version 4.2 or earlier; upgrade to a version where this vulnerability is patched if available.'}, {'type': 'list_item', 'content': "Restrict or monitor changes to logging configuration, especially the 'Log file name' field."}, {'type': 'list_item', 'content': 'Implement application whitelisting and endpoint protection to detect or block exploitation attempts.'}, {'type': 'list_item', 'content': 'If upgrading is not immediately possible, consider disabling or limiting logging features that accept user-supplied filenames.'}] [1, 4]

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