CVE-2026-86141 in libxml2
Summary
by MITRE • 09/05/2026
xmlregexp in libxml2 before 2.15.4 has a NULL pointer dereference in xmlRegNewParserCtxt after a strdup failure, i.e., it does not calculate a string length after NULL checking.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/05/2026
The vulnerability identified as CVE-2023-6987 resides within the libxml2 library, specifically affecting versions prior to 2.15.4. This issue centers on a critical memory management flaw in the xmlRegNewParserCtxt function, which is responsible for initializing context structures required for parsing regular expressions used by the XML processor. The core technical deficiency involves improper error handling following a dynamic memory allocation failure. When the strdup function fails to allocate sufficient memory and returns NULL, subsequent code attempts to calculate or utilize string lengths without verifying that the pointer is valid. This oversight leads directly to a null pointer dereference when the application tries to access members of the non-existent structure or perform operations on the null reference.
From an operational perspective, this vulnerability primarily impacts the stability and availability of applications relying on libxml2 for XML processing with regular expression capabilities. A successful exploitation attempt would result in an immediate crash of the affected process due to a segmentation fault. While this is classified as a denial-of-service condition rather than a remote code execution vector, it can be particularly disruptive in server environments where continuous uptime is critical. Attackers could potentially trigger this flaw by supplying crafted XML input containing malformed or excessively large regular expression patterns that cause memory allocation failures under specific system constraints, such as low available memory conditions.
The technical classification of this vulnerability aligns with CWE-476, which denotes a NULL Pointer Dereference. This category encompasses errors where software fails to check for null pointers before using them, leading to crashes or undefined behavior. In the context of the MITRE ATT&CK framework, this type of flaw is often associated with techniques that aim to disrupt service availability, although it does not directly map to specific offensive tactics unless leveraged as part of a broader attack chain designed to exhaust resources or destabilize infrastructure components. The lack of robust input validation and error handling in legacy codebases like older versions of libxml2 highlights the importance of rigorous memory safety practices during software development.
Mitigation strategies for this vulnerability are straightforward and center on immediate version updates. Organizations must upgrade libxml2 to version 2.15.4 or later, where the developers have implemented proper null checks following strdup calls. This ensures that if memory allocation fails, the function handles the error gracefully without attempting to dereference a null pointer. For environments unable to update immediately due to dependency constraints, applying runtime protections such as Address Sanitizers during testing phases can help identify similar issues in custom codebases. Additionally, implementing strict input validation on XML sources and limiting the complexity of regular expressions processed by the library can reduce the likelihood of triggering memory allocation failures that lead to this specific crash condition.