CVE-2019-25590: Axessh 4.2 Denial of Service Vulnerability

CVE-2019-25590 Overview

CVE-2019-25590 is a denial of service vulnerability affecting Axessh version 4.2, a Windows SSH and Telnet client developed by LabF. The vulnerability exists in the logging configuration functionality, where the application fails to properly validate the length of input supplied to the log file name field. This allows local attackers to crash the application by supplying an excessively long string (500 or more characters) in this parameter.

Critical Impact

Local attackers can cause a complete denial of service by crashing the Axessh application through a buffer overflow in the logging configuration, disrupting SSH and Telnet connectivity for affected users.

Affected Products

• Axessh version 4.2
• LabF Axessh Windows SSH/Telnet client

Discovery Timeline

• 2026-03-22 - CVE CVE-2019-25590 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2019-25590

Vulnerability Analysis

This vulnerability is classified under CWE-1282 (Assumed-Immutable Data is Stored in Writable Memory), which relates to improper handling of input data that the application assumes will not exceed expected boundaries. The attack requires local access to the system where Axessh is installed.

The vulnerability manifests when an attacker enables session logging within the Axessh application and provides an oversized input string in the log file name parameter. When this malformed configuration is used in conjunction with establishing a telnet connection, the application crashes due to the buffer overflow condition. While this is a local attack vector requiring no special privileges, it results in high confidentiality impact as the crash can potentially expose sensitive memory contents.

Root Cause

The root cause of this vulnerability is insufficient input validation in the Axessh logging configuration handler. The application does not properly check the length of the log file name parameter before processing it, allowing an attacker to supply a string that exceeds the allocated buffer size. When this oversized string is written to memory, it causes a buffer overflow condition that results in application termination.

Attack Vector

The attack is executed locally and requires the attacker to have access to the Axessh application interface. The exploitation process involves:

1. Launching the Axessh application on the target system
2. Enabling session logging functionality in the application settings
3. Pasting a buffer of 500 or more characters into the log file name field
4. Initiating a telnet connection to trigger the crash

The vulnerability does not require any authentication or special privileges to exploit, though it does require local access to the machine running Axessh.

For technical exploitation details, refer to the Exploit-DB #46858 entry or the VulnCheck Advisory on Axessh.

Detection Methods for CVE-2019-25590

Indicators of Compromise

• Unexpected Axessh application crashes or terminations
• Abnormally long strings present in Axessh configuration files or registry entries
• Event log entries indicating application crashes related to axessh.exe

Detection Strategies

• Monitor for Axessh process terminations that occur shortly after configuration changes
• Implement application crash monitoring solutions to detect abnormal Axessh behavior
• Review system event logs for axessh.exe crash dump entries with memory access violations

Monitoring Recommendations

• Configure application whitelisting to restrict access to Axessh configuration settings
• Implement endpoint detection and response (EDR) solutions like SentinelOne to monitor for exploitation attempts
• Enable verbose logging on endpoints to capture configuration changes to SSH/Telnet clients

How to Mitigate CVE-2019-25590

Immediate Actions Required

• Restrict local access to systems running Axessh version 4.2
• Consider disabling the session logging feature if not required for operations
• Implement access controls to prevent unauthorized users from modifying Axessh configurations
• Evaluate alternative SSH/Telnet clients if patches are unavailable

Patch Information

No vendor patch information is currently available for this vulnerability. Users should check the LabF Website or the Axessh Download Page for potential updates. Organizations should consider upgrading to newer versions of Axessh if available, or migrating to alternative SSH clients with better security maintenance.

Workarounds

• Disable the session logging feature in Axessh to prevent exploitation of this specific vulnerability
• Implement strict access controls limiting which users can access and configure Axessh
• Deploy endpoint protection solutions to monitor for application crashes and potential exploitation
• Consider using alternative SSH/Telnet clients such as PuTTY or OpenSSH for Windows until a patch is available