Integer overflow in Xmlsoft Libxml2

CVE-2026-86138

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

Vulnerability class: Integer Overflow

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.9 (Medium). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L.

EPSS exploit prediction

EPSS: 0.001 (2.5th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 2nd percentile — 2.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-86138: held from 0.001 to 0.001.

EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-86138?
CVE-2026-86138 is a medium-severity vulnerability in Xmlsoft Libxml2, classified under Integer Overflow or Wraparound. CVSS score: 6.9/10. Published 2026-09-05.
How severe is CVE-2026-86138?
Medium severity. CVSS v3 base score is 6.9 out of 10.