---
id: CVE-2025-1012
title: A race during concurrent delazification could have led to a use-after-free
summary: >-
  A race during concurrent delazification could have led to a use-after-free.
  This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR
  128.7, Thunderbird 128.7, and Thunderbird 135.
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
  - CWE-416
vendor: mozilla
product: firefox
affected:
  - firefox < 115.20.0
  - firefox < 135.0
  - 'firefox >= 128.1.0, < 128.7.0'
  - thunderbird < 135.0
  - 'thunderbird >= 128.0.1, < 128.7.0'
patched:
  - firefox 128.7.0
  - thunderbird 128.7.0
published: '2025-02-04'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T19:10:01.007'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-1012'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1939710'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-07/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-08/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-09/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-10/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-11/'
    label: security@mozilla.org
  - url: 'https://lists.debian.org/debian-lts-announce/2025/02/msg00005.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/02/msg00006.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00452
epssPercentile: 0.36946
ingestedAt: '2026-09-30T19:21:07.223Z'
---

## Overview

A race during concurrent delazification could have led to a use-after-free. This vulnerability was fixed in Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, and Thunderbird 135.

## Affected

- `firefox < 115.20.0`
- `firefox < 135.0`
- `firefox >= 128.1.0, < 128.7.0`
- `thunderbird < 135.0`
- `thunderbird >= 128.0.1, < 128.7.0`

## Remediation

Upgrade past the affected range:

- `firefox 128.7.0`
- `thunderbird 128.7.0`