Quick answers
- Is CVE-2026-56409 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-56409 being exploited in the wild.
- How severe is CVE-2026-56409?
- Medium severity, with a CVSS score of 6.5, published 21 June 2026.
- Which products and versions are affected?
- Libexpat Project Expat before 2.8.2.
- Is there a fix for CVE-2026-56409?
- A patch was published on 2026-06-01: Fix merged into master branch via Pull Request 1259 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-56409 attacked?
- It is attacked with local access, in a software library.
- Am I affected by CVE-2026-56409?
- 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 exists in the xmlwf utility of libexpat before version 2.8.2. The root cause is located in the main() function where the size calculation for the output path—combining the directory name and filename—is performed without proper overflow guards during addition and multiplication. When processing extremely long filenames with the '-d' (output directory) flag, the calculated buffer size can wrap around, leading to a heap-based buffer overflow during subsequent string copy operations (tcscpy/tcscat). An attacker could exploit this by providing a specially crafted filename to the utility, potentially achieving arbitrary code execution or a denial-of-service. The issue is fixed in version 2.8.2 by implementing SIZE_MAX guards.
Affected products
- libexpat project libexpat before 2.8.2
Timeline
- 2026-06-01: patched: Fix merged into master branch via Pull Request 1259
- 2026-06-21: advisory: CVE-2026-56409 published