Quick answers
- Is CVE-2026-56404 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-56404 being exploited in the wild.
- How severe is CVE-2026-56404?
- 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-2026-56404?
- A patch was published on 2026-05-29: Fix merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-56404 attacked?
- It is attacked with local access, in a software library.
- Am I affected by CVE-2026-56404?
- 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 vulnerability (CWE-190) exists in libexpat's `addBinding` function in `xmlparse.c`. The flaw occurs when calculating the length of a URI, specifically during a post-increment operation (`len++`) when a namespace separator is present. While URI lengths are currently bounded by pool block sizes, the signed integer increment can trigger undefined behavior at the boundary. An attacker could potentially exploit this to cause memory corruption or information disclosure. The issue is fixed in version 2.8.2.
Affected products
- libexpat project libexpat before 2.8.2
Timeline
- 2026-05-28: other: Fix proposed in pull request
- 2026-05-29: patched: Fix merged into master branch
- 2026-06-21: disclosed: CVE published