CVE-2026-86138: xmlsoft libxml2 Integer Overflow or Wraparound

Vulnerability summary

CVE-2026-86138 is a high (CVSS 7.8) Integer Overflow or Wraparound vulnerability in xmlsoft libxml2. EPSS estimates a 0.13% chance of exploitation in the next 30 days, higher than 2.4% of scored vulnerabilities.

Timeline

1. 05-09-2026
   PublishedVulnerability first disclosed.
2. 08-09-2026
   Last modifiedVulnerability information updated.

Description

In libxml2 before 2.15.4, xmlDictAddQString in dict.c has an integer overflow and resultant heap-based buffer overflow.

• CWE-190Integer Overflow or WraparoundThe product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.