Quick answers
- Is CVE-2026-56407 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-56407 being exploited in the wild.
- How severe is CVE-2026-56407?
- Medium severity, with a CVSS score of 6.9, published 21 June 2026.
- Which products and versions are affected?
- Libexpat Project Expat before 2.8.2.
- Is there a fix for CVE-2026-56407?
- A patch was published on 2026-06-03: Fix merged into master branch. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-56407 attacked?
- It is attacked with local access, in a software library.
- Am I affected by CVE-2026-56407?
- Check whether you run Libexpat Project Expat at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
An integer overflow exists in libexpat's 'doProlog' function, specifically within the 'storeEntityValue' logic. When processing internal entity declarations, the library stashes the replacement text length using a cast to a signed integer. If the entity value pool grows beyond INT_MAX, the 'textLen' value truncates to a negative integer. This causes subsequent entity references to calculate an incorrect 'textEnd' pointer that precedes the 'textPtr', resulting in an out-of-bounds buffer walk. The vulnerability is addressed in version 2.8.2 by capping the length before the integer cast.
Affected products
- libexpat project libexpat before 2.8.2
Timeline
- 2026-06-02: disclosed: Vulnerability reported via GitHub pull request after discovery through fuzzing.
- 2026-06-03: patched: Fix merged into master branch.
- 2026-06-21: advisory: CVE-2026-56407 published.