CVE-2019-13455 in Xymon
Summary
by MITRE
In Xymon through 4.3.28, a stack-based buffer overflow vulnerability exists in the alert acknowledgment CGI tool because of expansion in acknowledge.c.
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Analysis
by VulDB Data Team • 08/07/2020
The vulnerability identified as CVE-2019-13455 represents a critical stack-based buffer overflow within the Xymon monitoring system version 4.3.28 and earlier. This issue specifically affects the alert acknowledgment CGI tool, which is a core component responsible for managing and acknowledging system alerts within the Xymon framework. The vulnerability stems from improper handling of HTML entity expansion, particularly the character sequence, during the processing of user input in the acknowledge.c source file. This flaw creates a condition where an attacker can manipulate the input parameters to overflow the stack buffer, potentially leading to arbitrary code execution or system compromise. The affected Xymon versions through 4.3.28 represent a significant security risk for organizations relying on this monitoring solution for critical infrastructure management.
The technical exploitation of this vulnerability occurs through the manipulation of the alert acknowledgment interface where the HTML entity is processed without adequate bounds checking. When the acknowledge.c module processes user-provided data containing the character sequence, the expansion process causes the buffer to exceed its allocated memory boundaries. This buffer overflow creates opportunities for attackers to overwrite adjacent memory locations, potentially corrupting the program's execution flow and allowing for code injection attacks. The vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety issue in software development. The attack vector requires interaction with the web-based CGI interface, making it accessible to remote attackers who can craft malicious input to trigger the overflow condition.
The operational impact of this vulnerability extends beyond simple system instability, as it can lead to complete system compromise when exploited successfully. Organizations utilizing Xymon for network monitoring and alert management face potential unauthorized access to their monitoring infrastructure, which could result in data exfiltration, system manipulation, or complete service disruption. The vulnerability affects the core alert acknowledgment functionality, which means that attackers could potentially disrupt critical monitoring operations or gain elevated privileges within the system. The attack requires minimal prerequisites since it targets a publicly accessible web interface, making it particularly dangerous for environments where Xymon is deployed without proper network segmentation or access controls. According to ATT&CK framework, this vulnerability maps to T1203 Exploitation for Client Execution and T1059 Command and Scripting Interpreter, as successful exploitation would enable attackers to execute arbitrary commands on the affected system.
Mitigation strategies for CVE-2019-13455 should prioritize immediate patch application from the vendor, as version 4.3.29 and later releases contain the necessary fixes for this buffer overflow vulnerability. Organizations should implement network segmentation to limit access to the Xymon CGI interfaces, particularly restricting access to authorized personnel only. Input validation and sanitization should be enhanced at multiple layers including web application firewalls, proxy servers, and application-level defenses to prevent malicious payloads from reaching the vulnerable code paths. Security monitoring should be enhanced to detect unusual patterns in alert acknowledgment requests, which could indicate exploitation attempts. Additionally, implementing proper access controls and authentication mechanisms for the CGI interfaces will reduce the attack surface and make exploitation more difficult. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in other components of the monitoring infrastructure. The fix implemented by the vendor addresses the root cause by adding proper bounds checking and input validation for HTML entity expansion, specifically targeting the character sequence processing in the acknowledge.c module to prevent the stack buffer overflow condition from occurring.