---
id: CVE-2026-77214
title: >-
  libexpat before commit 13c5f63 contains a heap buffer over-read vulnerability
  in xmlparse.c
summary: >-
  libexpat before commit 13c5f63 contains a heap buffer over-read vulnerability
  in xmlparse.c. XML_ParseBuffer advances the parse buffer end with
  parser->m_bufferEnd += len using a caller-supplied length that is not
  validated against the a…
severity: high
cvss: 8.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L'
cwe:
  - CWE-125
vendor: libexpat
product: libexpat
affected:
  - libexpat <= 2.8.5
published: '2026-10-07'
updated: '2026-10-07'
sourceUpdated: '2026-10-07T15:57:20.793'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-77214'
references:
  - url: >-
      https://github.com/libexpat/libexpat/commit/13c5f63a7f1c52c2feee3b16a1134d4fb68e9ea0
    label: disclosure@vulncheck.com
  - url: 'https://github.com/libexpat/libexpat/pull/1393'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/libexpat-heap-buffer-over-read-in-xmlparse-c-via-xml-parsebuffer
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-07T15:36:04.056Z'
---

## Overview

libexpat before commit 13c5f63 contains a heap buffer over-read vulnerability in xmlparse.c. XML_ParseBuffer advances the parse buffer end with parser->m_bufferEnd += len using a caller-supplied length that is not validated against the allocated buffer size, so repeated XML_ParseBuffer calls move m_bufferEnd past the end of the heap allocation and subsequent parsing reads out of bounds. Reaching this path requires a parse buffer to already be present; otherwise XML_ParseBuffer returns XML_ERROR_NO_BUFFER. A buffer is present after a prior call to XML_GetBuffer, either directly (the common case) or indirectly through a prior XML_Parse call that allocates the buffer internally. The over-read discloses adjacent heap memory to the calling application, recovering heap pointers, libc function pointers, and code pointers sufficient to defeat ASLR and build further exploitation primitives.

## Remediation

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