CVE-2019-25590 in Axessh
Summary
by MITRE • 03/22/2026
Axessh 4.2 contains a denial of service vulnerability in the logging configuration that allows local attackers to crash the application by supplying an excessively long string in the log file name field. Attackers can enable session logging, paste a buffer of 500 or more characters into the log file name parameter, and trigger a crash when establishing a telnet connection.
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Analysis
by VulDB Data Team • 03/23/2026
The vulnerability identified as CVE-2019-25590 resides within Axessh 4.2, a telnet and ssh client application that has been found to contain a critical denial of service flaw in its logging configuration mechanism. This vulnerability specifically targets the application's handling of log file names and represents a classic buffer overflow scenario that can be exploited by local attackers to cause application instability. The flaw manifests when the application processes user-supplied input for log file naming parameters, creating a scenario where insufficient input validation leads to memory corruption during normal operation. The vulnerability operates through a straightforward attack vector that does not require network access or elevated privileges, making it particularly concerning for environments where local user access is not strictly controlled.
The technical exploitation of this vulnerability occurs through a well-defined sequence of actions that leverages the application's session logging functionality. When attackers enable session logging and subsequently provide a buffer containing 500 or more characters into the log file name parameter, the application fails to properly handle this excessive input length. This condition triggers a memory management error that results in the application crashing when a telnet connection is subsequently established. The flaw demonstrates characteristics consistent with CWE-121, which describes heap-based buffer overflow conditions, and represents a specific implementation weakness where string handling routines do not properly validate input boundaries before processing. The vulnerability's impact is amplified by the fact that it can be triggered through normal application usage patterns, making it difficult to distinguish between legitimate and malicious input without proper input sanitization measures.
The operational impact of CVE-2019-25590 extends beyond simple application instability to potentially disrupt service availability and compromise system integrity within environments where Axessh is deployed. Local attackers who can access the system and manipulate application configuration parameters can effectively deny service to legitimate users by causing repeated application crashes. This vulnerability particularly affects systems where telnet connectivity is frequently established and where logging is enabled as part of standard operational procedures. The attack requires minimal technical expertise and can be executed through simple parameter manipulation, making it an attractive target for adversaries seeking to disrupt operations. Organizations using Axessh 4.2 may experience service interruptions, logging failures, and potential data loss during crash recovery periods, especially in mission-critical environments where continuous availability is essential.
Mitigation strategies for CVE-2019-25590 should focus on input validation and boundary checking within the application's logging subsystem. The most effective immediate solution involves implementing strict character limit enforcement on log file name parameters, ensuring that no input exceeds predetermined safe boundaries. System administrators should disable session logging functionality when it is not required, and implement proper access controls to limit local user privileges that can manipulate application configuration parameters. The vulnerability aligns with ATT&CK technique T1499.004, which covers network disruption through resource exhaustion, and organizations should consider implementing monitoring solutions that can detect unusual application crash patterns. Regular application updates and patches should be deployed as soon as vendor fixes become available, while network segmentation and privilege separation can help limit the potential impact of exploitation. Additionally, implementing proper logging mechanisms that can detect and alert on malformed input attempts can provide early warning of potential exploitation attempts.