---
id: CVE-2026-118370
title: >-
  libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and
  nPrefixes
summary: >-
  libexpat through 2.9.0 contains a signed integer overflow vulnerability in
  storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds
  writes via oversized attribute counts. Attackers can supply a multi-gigabyte
  document…
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-190
vendor: libexpat
product: libexpat
affected:
  - libexpat <= 2.9.0
published: '2026-10-28'
updated: '2026-10-28'
sourceUpdated: '2026-10-28T02:03:19.447Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-118370'
references:
  - url: 'https://github.com/libexpat/libexpat/pull/1450'
  - url: >-
      https://github.com/libexpat/libexpat/commit/1bac53c4fc460a03cd9860f39501c7979f6750ae
  - url: >-
      https://github.com/libexpat/libexpat/commit/621cb2c78b253ee023a86bc91d6ddb048481c04c
  - url: >-
      https://github.com/libexpat/libexpat/blob/a76b1174c1ea52abb639a4c69d52b630a8a106a2/expat/lib/xmlparse.c#L4138-L4140
  - url: 'https://github.com/libexpat/libexpat'
  - url: >-
      https://www.vulncheck.com/advisories/libexpat-through-2.9.0-integer-overflow-in-storeatts-via-attindex-and-nprefixes
    label: >-
      VulnCheck Advisory: libexpat through 2.9.0 Integer Overflow in storeAtts
      via attIndex and nPrefixes
tags:
  - cve.org
ingestedAt: '2026-10-28T03:02:57.627Z'
---

## Overview

libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.

## Affected

- `libexpat <= 2.9.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.