# CVE-2026-86137: libxml2 out-of-bounds read in xmlregexp NXT macro

Source: https://junglewise.ai/threats/cve-2026-86137-libxml2-out-of-bounds-read-in-xmlregexp-nxt-macro  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-05. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-86137 · Severity: low · CVSS 2.9 · Published 2026-09-05

libxml2 is a widely-used XML parsing library integrated into many applications and operating systems. A flaw in the regular expression parser could allow an attacker to trigger out-of-bounds memory access by providing a specially crafted XML document, potentially causing an application crash or information disclosure.

Technologies: [Xmlsoft Libxml2](https://junglewise.ai/threats/technologies/libxml2). Vendors: [Xmlsoft](https://junglewise.ai/threats/vendors/xmlsoft).

## Quick answers

**Is CVE-2026-86137 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86137 being exploited in the wild.

**How severe is CVE-2026-86137?** Low severity, with a CVSS score of 2.9, published 5 September 2026.

**Which products and versions are affected?** GNOME libxml2 before 2.15.4.

**Is there a fix for CVE-2026-86137?** A patch was published on 2026: Fixed in libxml2 2.15.4 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-86137 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-86137?** Check whether you run Xmlsoft Libxml2. 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 out-of-bounds read vulnerability exists in the NXT macro within the xmlregexp.c file, specifically in the xmlFAParsePosCharGroup function. The vulnerability occurs due to insufficient bounds checking when accessing memory via the macro, allowing an attacker to read beyond the allocated string buffer. The attack requires parsing a malicious XML regular expression pattern; no authentication is required. The flaw can result in denial of service or potential information exposure. The vulnerability has been patched in libxml2 version 2.15.4 with bounds checking added to the NXT macro definition.

## Affected products

- GNOME libxml2 before 2.15.4

## Timeline

- 2026-09-05: disclosed
- 2026: patched: Fixed in libxml2 2.15.4

## References

- [https://github.com/GNOME/libxml2/commit/76fe08d97de88bfaef2f7d5cd27f11954cc5bee2](https://github.com/GNOME/libxml2/commit/76fe08d97de88bfaef2f7d5cd27f11954cc5bee2)
- [https://github.com/GNOME/libxml2/compare/v2.15.3...v2.15.4](https://github.com/GNOME/libxml2/compare/v2.15.3...v2.15.4)

## Related threats

- [libxml2 xinclude parseFlags not propagated](https://junglewise.ai/threats/cve-2026-86144-libxml2-xinclude-parseflags-not-propagated)
- [libxml2 integer overflow in xmlOutputWriteCallback](https://junglewise.ai/threats/cve-2026-86143-libxml2-integer-overflow-in-xmloutputwritecallback)
- [libxml2 heap buffer overflow in xmlXPtrEvalXPtrPart](https://junglewise.ai/threats/cve-2026-86142-libxml2-heap-buffer-overflow-in-xmlxptrevalxptrpart)
- [libxml2 NULL pointer dereference in xmlRegNewParserCtxt](https://junglewise.ai/threats/cve-2026-86141-libxml2-null-pointer-dereference-in-xmlregnewparserctxt)
- [libxml2 stack-based buffer overflow in xmlSnprintfElements](https://junglewise.ai/threats/cve-2026-86140-libxml2-stack-based-buffer-overflow-in-xmlsnprintfelements)