---
id: "CVE-2026-117610"
kind: "vulnerability"
aliases: ["CVE-2026-117610"]
title: "libexpat: crafted XML chunking crashes parser via NULL pointer dereference"
severity: "high"
cvss: 8.2
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "libexpat", "fixed": [], "affected": "<= 2.9.0", "ecosystem": "c"}]
ecosystems: []
tags: ["c", "libexpat", "package", "perl", "python", "self-hosted"]
not_affected_if: ["no-streaming-xml-parsing", "trusted-input-only"]
published_at: "2026-10-28T03:17:12+00:00"
first_seen_at: "2026-10-28T03:31:02+00:00"
updated_at: "2026-10-28T03:33:33+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117610", "first_seen_at": "2026-10-28T03:31:02+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-28T03:33:33+00:00"}]
---

# libexpat: crafted XML chunking crashes parser via NULL pointer dereference

libexpat through 2.9.0 has a NULL pointer dereference in externalEntityInitProcessor2() when parsing external entities with empty non-final input. An attacker who controls how XML is chunked into the parser can crash the application that uses it.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- c:libexpat affected <= 2.9.0 fixed ?

## How to check

- Find the libexpat version: 'pkg-config --modversion expat', 'dpkg -l libexpat1', or 'rpm -q expat'; every version up to and including 2.9.0 is listed as affected.
- Python (pyexpat), Perl XML::Parser and other bindings bundle or link libexpat: check 'python -c "import pyexpat; print(pyexpat.EXPAT_VERSION)"'.
- Exposure needs the app to feed untrusted XML in chunks and to handle external entities (XML_ExternalEntityParserCreate).

## Fix

No fixed libexpat release known as of 2026-10-28 (latest 2.9.0 is listed as affected). Watch https://github.com/libexpat/libexpat/blob/master/expat/Changes and distro trackers for the next release after 2.9.0.

## Timeline

- 2026-10-28T03:31:02+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117610
- 2026-10-28T03:33:33+00:00 analyst — No vendor advisory for this CVE found. libexpat master Changes lists 2.9.0 (2026-10-05) as latest and has no entry for it, so no fixed release is known; tracker #1160 lists several unvalidated non-public issues (PR #1444 opened 2026-10-26, unconfirmed as this one). The similar-sounding CVE-2026-32776 (fixed in 2.7.5) is a different bug. No X chatter, no PoC. Nothing verified.

## Documents

- [mentions] libexpat Changes (master): latest release 2.9.0, no entry for this CVE https://raw.githubusercontent.com/libexpat/libexpat/master/expat/Changes
- [mentions] libexpat #1160: Unfixed non-public security issues https://github.com/libexpat/libexpat/issues/1160

## From the sources

libexpat through 2.9.0 contains a NULL pointer dereference vulnerability in externalEntityInitProcessor2() in lib/xmlparse.c that mishandles the XML_TOK_NONE token from empty input. Attackers who control stream chunking can force an empty non-final first parse on an external entity subparser, causing a later parse to crash the application.

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