---
id: CVE-2025-4087
title: >-
  A vulnerability was identified in Thunderbird where XPath parsing could
  trigger undefined behavior due to missing null checks during attribute access
summary: >-
  A vulnerability was identified in Thunderbird where XPath parsing could
  trigger undefined behavior due to missing null checks during attribute access.
  This could lead to out-of-bounds read access and potentially, memory
  corruption. This …
severity: medium
cvss: 4.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-125
vendor: mozilla
product: firefox
affected:
  - firefox < 128.10
  - firefox < 138.0
  - thunderbird < 128.10.0
  - thunderbird < 138.0
patched:
  - firefox 138.0
  - thunderbird 138.0
published: '2025-04-29'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-4087'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1952465'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-28/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-29/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-31/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-32/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00024.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00317
epssPercentile: 0.2228
ingestedAt: '2026-09-30T18:17:24.434Z'
---

## Overview

A vulnerability was identified in Thunderbird where XPath parsing could trigger undefined behavior due to missing null checks during attribute access. This could lead to out-of-bounds read access and potentially, memory corruption. This vulnerability was fixed in Firefox 138, Firefox ESR 128.10, Thunderbird 138, and Thunderbird 128.10.

## Affected

- `firefox < 128.10`
- `firefox < 138.0`
- `thunderbird < 128.10.0`
- `thunderbird < 138.0`

## Remediation

Upgrade past the affected range:

- `firefox 138.0`
- `thunderbird 138.0`