CVE-2019-13486 in Xymon
Summary
by MITRE
In Xymon through 4.3.28, a stack-based buffer overflow exists in the status-log viewer component because of expansion in svcstatus.c.
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Analysis
by VulDB Data Team • 08/07/2020
The vulnerability CVE-2019-13486 represents a critical stack-based buffer overflow in the Xymon monitoring system version 4.3.28 and earlier. This flaw resides within the status-log viewer component, specifically in the svcstatus.c source file where improper handling of HTML entity expansion creates conditions for malicious input to overwrite adjacent stack memory. The vulnerability stems from insufficient bounds checking when processing user-supplied data that contains HTML entities such as which are commonly used to represent non-breaking spaces in web content. Attackers can exploit this weakness by crafting malicious input containing specially formatted HTML entities that trigger the buffer overflow during the expansion process.
The technical implementation of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to write beyond the allocated buffer boundaries. The flaw occurs during the parsing and rendering of status logs where the system processes HTML entities without adequate input validation or size constraints. When the entity expansion occurs, the system attempts to convert the entity into its corresponding character representation while simultaneously managing stack memory allocation. The absence of proper input sanitization means that maliciously crafted input can cause the expansion routine to write beyond the intended buffer limits, potentially corrupting adjacent stack memory and creating opportunities for arbitrary code execution.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can enable remote code execution on systems running vulnerable versions of Xymon. An attacker who can influence the status log content or submit crafted input to the monitoring system can potentially gain control over the affected system. This represents a significant concern for organizations relying on Xymon for network monitoring and system health tracking, as the vulnerability could be exploited through various attack vectors including web interface access or log injection scenarios. The stack-based nature of the overflow makes exploitation more predictable and potentially more reliable compared to heap-based vulnerabilities, as stack memory layout is more consistent and accessible.
Mitigation strategies for CVE-2019-13486 should prioritize immediate patching of affected systems to version 4.3.29 or later, which contains the necessary fixes for the buffer overflow vulnerability. Organizations should implement input validation and sanitization measures to prevent malicious HTML entities from reaching the vulnerable parsing routines, including the use of proper HTML escaping mechanisms and strict content filtering. Network segmentation and access controls should be strengthened to limit exposure of the affected components, while monitoring systems should be configured to detect unusual patterns in status log submissions that might indicate exploitation attempts. The vulnerability also highlights the importance of secure coding practices around memory management and input validation, particularly when processing user-supplied data in web-based monitoring interfaces. Security teams should conduct thorough assessments of their Xymon deployments to identify all instances of the vulnerable component and ensure comprehensive remediation across their monitoring infrastructure.