# CVE-2026-117610: libexpat NULL pointer dereference in external entity parsing

Source: https://junglewise.ai/threats/cve-2026-117610-libexpat-through-2-9-0-contains-a-null-pointer-dereference  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-28. Updated: 2026-10-28  
License: CC BY 4.0 with a link back

CVE-2026-117610 · Severity: medium · CVSS 5.9 · Published 2026-10-28

libexpat is an XML parser library used in many applications and systems to process XML files. A vulnerability in how it handles external entity parsing can cause applications using the library to crash when processing specially crafted XML streams. An attacker who controls the source of XML data could exploit this to cause a denial of service.

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

## Quick answers

**Is CVE-2026-117610 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-117610 being exploited in the wild.

**How severe is CVE-2026-117610?** Medium severity, with a CVSS score of 5.9, published 28 October 2026.

**Which products and versions are affected?** Libexpat through 2.9.0.

**Is there a fix for CVE-2026-117610?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-117610 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-117610?** Check whether you run Libexpat 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

The vulnerability is a NULL pointer dereference in externalEntityInitProcessor2() in xmlparse.c that occurs when handling XML_TOK_NONE tokens from empty input. An attacker who controls stream chunking can force an empty non-final first parse on an external entity subparser, leading to a crash on a subsequent parse operation. This is a denial-of-service vulnerability requiring the ability to control XML input to an application.

## Affected products

- libexpat libexpat through 2.9.0

## Timeline

- 2026-10-28: disclosed

## References

- [https://github.com/libexpat/libexpat](https://github.com/libexpat/libexpat)
- [https://github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c](https://github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c)

## Related threats

- [libexpat out-of-bounds read in unknown encoding handlers](https://junglewise.ai/threats/cve-2026-124317-libexpat-through-2-10-0-contains-an-out-of-bounds-read)
- [libexpat denial of service in billion laughs protection](https://junglewise.ai/threats/cve-2026-115506-libexpat-through-2-9-0-contains-a-denial-of-service)
- [libexpat denial of service via XML_ParserReset byte count inconsistency](https://junglewise.ai/threats/cve-2026-113351-libexpat-2-7-2-through-2-9-0-contains-a-denial-of-service)