CVE-2026-0992 in libxml2
Summary
by MITRE • 01/15/2026
A flaw was found in the libxml2 library. This uncontrolled resource consumption vulnerability occurs when processing XML catalogs that contain repeated <nextCatalog> elements pointing to the same downstream catalog. A remote attacker can exploit this by supplying crafted catalogs, causing the parser to redundantly traverse catalog chains. This leads to excessive CPU consumption and degrades application availability, resulting in a denial-of-service condition.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2026-0992 represents a critical resource consumption flaw within the libxml2 library, a widely deployed XML parsing component used across numerous applications and systems. This issue manifests when the library processes XML catalogs containing repeated <nextCatalog> elements that reference identical downstream catalogs, creating an exploitable condition that can be leveraged by remote attackers to perform denial-of-service attacks. The flaw specifically resides in the catalog processing mechanism where the parser fails to properly track previously visited catalog entries, leading to infinite or excessively deep traversal sequences. The vulnerability impacts systems that rely on libxml2 for XML catalog resolution, particularly those that process untrusted XML content or external catalog references, making it a significant concern for web applications, middleware systems, and any software that utilizes XML catalog functionality for resource management. The issue stems from inadequate state tracking during catalog chain traversal, allowing maliciously constructed XML catalogs to cause the parser to repeatedly follow the same reference paths without proper cycle detection.
The technical implementation of this vulnerability exploits the fundamental parsing behavior of libxml2 when handling XML catalog files, which are used to map external identifiers to local resources. When the parser encounters a <nextCatalog> element, it should maintain a record of previously processed catalogs to prevent redundant traversal. However, the flaw allows the parser to continue following catalog references indefinitely, even when they point to catalogs that have already been processed. This results in exponential CPU consumption as the parser becomes trapped in a cycle of redundant catalog resolution attempts. The vulnerability is particularly dangerous because it can be triggered through any XML catalog processing operation, including those that occur during application startup, configuration loading, or dynamic content processing. The resource consumption occurs primarily in the CPU processing time required to traverse the catalog chains rather than memory allocation, making it difficult to detect through standard memory monitoring tools. This behavior aligns with CWE-400, which categorizes uncontrolled resource consumption as a vulnerability where an application fails to properly limit resource consumption, and maps to ATT&CK technique T1499.100 which covers resource exhaustion attacks targeting application availability.
The operational impact of CVE-2026-0992 extends beyond simple denial-of-service conditions, as it can severely disrupt system availability and potentially cause cascading failures in applications that depend on XML processing. Systems experiencing this vulnerability may show significant performance degradation, with CPU utilization reaching 100% for extended periods, effectively rendering applications unresponsive to legitimate requests. The attack vector is particularly insidious because it requires minimal privileges and can be executed against any system that processes XML catalogs, including web servers, application servers, and backend services. Organizations using libxml2 versions prior to the patched release face elevated risk, especially those that process external or user-provided XML content, as attackers can craft malicious catalogs to trigger the vulnerability. The vulnerability also impacts automated systems that rely on XML catalog resolution for configuration management, deployment processes, or integration workflows, potentially causing widespread service disruption. Recovery from such attacks typically requires system restarts or manual intervention to clear parser states, making the impact both immediate and disruptive to business operations. This vulnerability demonstrates the importance of proper input validation and state management in parsing libraries, as it shows how seemingly benign XML catalog structures can be weaponized to exhaust system resources. The flaw's exploitation does not require sophisticated attack techniques, making it accessible to threat actors of varying skill levels and increasing the overall risk exposure for affected systems. Organizations should consider implementing network-level protections such as rate limiting and content filtering to mitigate potential exploitation while awaiting official patches.
Mitigation strategies for CVE-2026-0992 should focus on immediate defensive measures combined with long-term remediation approaches to protect against exploitation. The primary recommended action is to upgrade to the patched version of libxml2 that addresses the catalog traversal logic and implements proper cycle detection mechanisms. System administrators should prioritize patching all affected systems, particularly those handling external XML content or processing user-provided catalogs. Additionally, implementing input validation controls can help prevent exploitation by filtering or rejecting XML catalogs containing suspicious patterns of repeated <nextCatalog> elements. Network-level protections such as XML content filtering, rate limiting on XML processing requests, and monitoring for unusual CPU consumption patterns can provide additional defense-in-depth measures. Organizations should also consider implementing application-level restrictions that limit the depth of catalog chain traversal or set maximum processing time limits for XML catalog operations. Security teams should monitor for potential exploitation attempts through log analysis, looking for patterns of repeated catalog processing or unusual resource consumption. The vulnerability highlights the need for comprehensive testing of XML processing components, particularly in environments that process external or untrusted XML content, and emphasizes the importance of maintaining current security patches for core libraries. Implementing proper monitoring and alerting for resource consumption anomalies can help detect exploitation attempts before they cause significant service disruption. Regular security assessments of XML processing workflows and catalog management practices should be conducted to identify and remediate similar vulnerabilities in other components of the system architecture.