CVE-2026-86142

A flaw in libxml2's xmlXPtrEvalXPtrPart function allows a local attacker to cause a heap-based buffer overflow. An integer overflow while processing an oversized xpointer() expression leads to incorrect memory allocation and an out-of-bounds write, potentially resulting in information disclosure, data corruption, or a denial of service (DoS).

A heap-based buffer overflow in libxml2's xmlXPtrEvalXPtrPart function enables an out-of-bounds write during the evaluation of oversized xpointer() expressions. The flaw is assigned a Moderate severity rating because exploitation strictly requires local access and complex, multi-gigabyte payload inputs, effectively mitigating the threat of remote or automated system compromise.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this applications should avoid passing untrusted XPointer expressions into xmlXPtrEval or XInclude xpointer= attributes and strictly cap input length well below INT_MAX. Additionally, administrators should enforce process or cgroup memory limits to prevent the construction of multi-gigabyte scheme bodies, relying on heap allocator hardening rather than standard fortify flags, which cannot stop this byte-store loop.