# CVE-2026-56410: libexpat xmlwf integer overflow in resolveSystemId

Source: https://junglewise.ai/threats/cve-2026-56410-libexpat-xmlwf-integer-overflow-in-resolvesystemid  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-21. Updated: 2026-06-21  
License: CC BY 4.0 with a link back

CVE-2026-56410 · Severity: medium · CVSS 6.9 · Published 2026-06-21

libexpat is a widely used C library for parsing XML data. A vulnerability in its 'xmlwf' utility could allow an attacker to cause a system crash or potentially execute unauthorized code by providing a specially crafted XML file. This could impact the reliability of applications processing external XML data and potentially lead to data breaches or service disruptions.

Technologies: [Libexpat Project Expat](https://junglewise.ai/threats/technologies/expat). Vendors: [Libexpat Project](https://junglewise.ai/threats/vendors/libexpat-project).

## Quick answers

**Is CVE-2026-56410 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56410 being exploited in the wild.

**How severe is CVE-2026-56410?** 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-2026-56410?** A patch was published on 2026-05-31: Fix merged into master branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56410 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-56410?** 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 resolveSystemId function within the xmlwf utility of libexpat before version 2.8.2. The flaw occurs during the calculation of memory allocation size for absolute paths, specifically when processing external entity SYSTEM identifiers. On wide-character builds, the multiplication of string lengths by the character size can wrap around, leading to an undersized heap allocation. Subsequent string copy operations (tcscpy/tcscat) then result in a heap-based buffer overflow. An attacker could exploit this by providing a malicious XML file to be processed by xmlwf, potentially achieving arbitrary code execution or causing a denial of service. The issue is addressed in version 2.8.2.

## Affected products

- libexpat project libexpat before 2.8.2

## Timeline

- 2026-05-29: other: Initial patch proposed on GitHub
- 2026-05-31: patched: Fix merged into master branch
- 2026-06-21: disclosed: CVE published

## References

- [https://github.com/libexpat/libexpat/pull/1252](https://github.com/libexpat/libexpat/pull/1252)

## Related threats

- [libexpat use-after-free in doCdataSection](https://junglewise.ai/threats/cve-2026-56412-libexpat-use-after-free-in-docdatasection)
- [libexpat integer overflow in xmlwf endDoctypeDecl](https://junglewise.ai/threats/cve-2026-56411-libexpat-integer-overflow-in-xmlwf-enddoctypedecl)
- [libexpat xmlwf integer overflow in output filename handling](https://junglewise.ai/threats/cve-2026-56409-libexpat-xmlwf-integer-overflow-in-output-filename-handling)
- [libexpat integer overflow in copyString](https://junglewise.ai/threats/cve-2026-56408-libexpat-integer-overflow-in-copystring)
- [libexpat integer overflow in doProlog entity handling](https://junglewise.ai/threats/cve-2026-56407-libexpat-integer-overflow-in-doprolog-entity-handling)