CVE-2019-25607: Axessh 4.2 Buffer Overflow Vulnerability

CVE-2019-25607 Overview

CVE-2019-25607 is a stack-based buffer overflow vulnerability affecting Axessh version 4.2, a Windows-based SSH client developed by LabF. The vulnerability exists in the log file name field, allowing local attackers to execute arbitrary code by supplying an excessively long filename. When a user specifies a log file name exceeding 214 bytes, the buffer overflows and overwrites the instruction pointer (EIP), enabling attackers to redirect execution flow and run shellcode with system privileges.

Critical Impact

Local attackers can achieve arbitrary code execution with elevated system privileges by exploiting this buffer overflow vulnerability, potentially leading to complete system compromise.

Affected Products

• Axessh 4.2
• LabF Axessh SSH Client (Windows)

Discovery Timeline

• 2026-03-22 - CVE CVE-2019-25607 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2019-25607

Vulnerability Analysis

The vulnerability is classified as CWE-787 (Out-of-Bounds Write), which represents a critical memory corruption issue. The Axessh application fails to properly validate the length of input provided to the log file name field before copying it into a fixed-size stack buffer. When a filename exceeding the buffer's capacity is provided, the excess data overwrites adjacent stack memory, including the saved return address (instruction pointer).

The exploitation boundary occurs at exactly 214 bytes. Any input beyond this offset directly overwrites the EIP register, giving attackers precise control over program execution flow. This allows for reliable exploitation without requiring sophisticated techniques like heap spraying or information leaks.

Multiple public exploits are available on Exploit-DB #46858 and Exploit-DB #46922, with accompanying shellcode documented in Exploit-DB Shellcode #46281.

Root Cause

The root cause of this vulnerability is the absence of input length validation when handling the log file name parameter. The application uses an unsafe string copy operation that does not check whether the destination buffer can accommodate the source string, resulting in a classic stack-based buffer overflow condition. This type of vulnerability is commonly introduced when legacy C/C++ string functions like strcpy() or sprintf() are used without proper bounds checking.

Attack Vector

The attack vector is local, requiring the attacker to have access to the system where Axessh is installed. The attacker crafts a malicious log file name string consisting of:

1. 214 bytes of padding - Filler data to reach the buffer boundary
2. 4 bytes for EIP overwrite - The return address pointing to attacker-controlled shellcode or a return-oriented programming (ROP) gadget
3. Shellcode payload - Malicious code that executes upon return from the vulnerable function

Since the vulnerability executes with the privileges of the Axessh application, successful exploitation can result in code execution with system-level privileges if the application runs with elevated permissions.

Detection Methods for CVE-2019-25607

Indicators of Compromise

• Presence of abnormally long log file names (exceeding 214 characters) in Axessh configuration or command-line parameters
• Unexpected crashes or exceptions in the Axessh process indicating potential exploitation attempts
• Suspicious shellcode patterns or NOP sleds in log file path strings
• Evidence of unauthorized code execution following Axessh process termination

Detection Strategies

• Monitor for Axessh process crashes or abnormal terminations that may indicate exploitation attempts
• Implement application whitelisting to detect unauthorized code execution following Axessh compromise
• Deploy endpoint detection and response (EDR) solutions capable of identifying buffer overflow exploitation patterns
• Use SentinelOne's behavioral AI to detect process injection and shellcode execution following application compromise

Monitoring Recommendations

• Enable Windows Event Log monitoring for application crashes and exceptions related to Axessh
• Monitor for unusual child processes spawned by the Axessh application
• Implement file integrity monitoring on Axessh installation directories
• Track command-line arguments passed to Axessh for suspicious patterns or excessive string lengths

How to Mitigate CVE-2019-25607

Immediate Actions Required

• Discontinue use of Axessh 4.2 until a patched version is available from the vendor
• Consider migrating to alternative SSH clients with better security track records
• Restrict local user access to systems where Axessh is installed
• Implement application control policies to prevent unauthorized execution

Patch Information

No official patch information is currently available from the vendor. Users should check the LabF Homepage for security updates. The VulnCheck Advisory on Axessh provides additional details on the vulnerability status.

Workarounds

• Remove or disable the Axessh application if not required for business operations
• Implement strict access controls to limit which users can execute Axessh
• Deploy SentinelOne endpoint protection to detect and prevent exploitation attempts through behavioral analysis
• Use application sandboxing to contain potential exploitation impact
• Monitor and restrict the log file path configuration to prevent malicious input

Since the vulnerability requires local access, restricting user permissions and implementing least-privilege principles can significantly reduce the attack surface. Additionally, deploying modern endpoint protection solutions with exploit prevention capabilities provides defense-in-depth against buffer overflow attacks.