CVE-2026-86143: Xmlsoft LIBXML2

High severity, CVSS 7.3. EPSS: 0.2% chance of exploitation in the next 30 days.

In xmlIO in libxml2 before 2.15.4, an inconsistency in xmlOutputWriteCallback and xmlBufUse causes negative lengths to reach write callbacks, aka a lack of a check for integer overflow before calling writecallback. This has security relevance for many types of uses of that length value within a callback.

Affected products

• Xmlsoft LIBXML2: before 2.15.4 (fixed in 2.15.4)

Published 2026-09-05. Last modified 2026-09-15.