CVE-2019-13484 in Xymon
Summary
by MITRE
In Xymon through 4.3.28, a buffer overflow exists in the status-log viewer CGI because of expansion in appfeed.c.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/07/2020
The vulnerability identified as CVE-2019-13484 affects Xymon versions through 4.3.28 and represents a critical buffer overflow condition within the status-log viewer CGI component. This flaw stems from improper handling of character sequences during text processing in the appfeed.c source file, creating an exploitable condition that could allow remote attackers to execute arbitrary code or cause system instability. The issue manifests when the web interface processes log data containing specific HTML entity expansions, particularly the non-breaking space character representation that gets converted into multiple bytes during parsing operations. This buffer overflow vulnerability falls under the category of CWE-121, which describes stack-based buffer overflow conditions, and aligns with ATT&CK technique T1190 for exploiting buffer overflow vulnerabilities in web applications. The vulnerability is particularly concerning as it exists within a core monitoring component that typically runs with elevated privileges and handles sensitive system status information.
The technical implementation of this flaw occurs during the processing of status log data through the web-based interface where the application fails to properly validate or limit the length of input strings when expanding HTML entities like . When a malicious user submits specially crafted log entries containing extended sequences of these entities, the application's buffer handling routines do not account for the expanded byte length, leading to memory corruption that can be leveraged for code execution. The buffer overflow specifically impacts the status-log viewer CGI module, which serves as the primary interface for accessing system monitoring data. This vulnerability demonstrates poor input validation practices and inadequate bounds checking in the text processing pipeline, allowing attackers to overwrite adjacent memory locations with controlled data. The flaw is exacerbated by the fact that the application's CGI interface typically operates with sufficient privileges to potentially allow full system compromise.
The operational impact of CVE-2019-13484 extends beyond simple denial of service conditions to encompass potential full system compromise and unauthorized access to monitoring data. An attacker who successfully exploits this vulnerability could gain remote code execution capabilities on the affected system, potentially allowing them to escalate privileges, install persistent backdoors, or access sensitive system information. The monitoring nature of Xymon makes this particularly dangerous as the compromised system could provide attackers with insights into network infrastructure, system performance metrics, and security events that would otherwise be protected. Additionally, the vulnerability could be exploited to corrupt log files, making it difficult for administrators to track legitimate system issues or security incidents. This impacts both the availability and integrity of the monitoring infrastructure, potentially masking other security breaches or creating false negatives in security alerting systems.
Mitigation strategies for CVE-2019-13484 should prioritize immediate patching of affected Xymon installations to version 4.3.29 or later, which contains the necessary code modifications to prevent buffer overflow conditions. Organizations should implement network segmentation and access controls to limit exposure of the affected CGI interface to trusted networks only, reducing the attack surface for potential exploitation attempts. Input validation should be strengthened at multiple layers including web application firewalls that can detect and block malicious HTML entity sequences before they reach the vulnerable code paths. Security monitoring should be enhanced to detect unusual patterns in log file access or processing that might indicate exploitation attempts. The fix implemented in the patched version addresses the root cause by implementing proper bounds checking during HTML entity expansion and ensuring that buffer allocations account for potential expansion factors. Regular security assessments and code reviews should be conducted to identify similar vulnerabilities in other components of the monitoring infrastructure, particularly those involving text processing and memory management operations. System administrators should also consider implementing automated patch management processes to ensure timely deployment of security updates across all monitoring systems.