---
id: CVE-2026-12294
title: 'Sandbox escape in the DOM: Workers component'
summary: >-
  Sandbox escape in the DOM: Workers component. This vulnerability was fixed in
  Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and
  Thunderbird 140.12.
severity: critical
cvss: 9.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H'
cwe:
  - CWE-693
  - CWE-266
vendor: mozilla
product: firefox
affected:
  - firefox < 115.37.0
  - firefox < 152.0.0
  - 'firefox >= 128.0, < 140.12.0'
  - thunderbird < 140.12.0
  - thunderbird < 152.0.0
patched:
  - firefox 140.12.0
  - thunderbird 152.0.0
published: '2026-06-16'
updated: '2026-07-07'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-12294'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=2039873'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-57/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-58/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-59/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-60/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-61/'
    label: security@mozilla.org
  - url: 'https://access.redhat.com/errata/RHSA-2026:27717'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:27733'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:27734'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:29940'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:30846'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:33445'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:36100'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:36101'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:36102'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:36103'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-12294'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2489207'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12294.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
epss: 0.00363
epssPercentile: 0.30151
ingestedAt: '2026-07-07T13:53:11.824Z'
---

## Overview

Sandbox escape in the DOM: Workers component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

## Affected

- `firefox < 115.37.0`
- `firefox < 152.0.0`
- `firefox >= 128.0, < 140.12.0`
- `thunderbird < 140.12.0`
- `thunderbird < 152.0.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.12.0`
- `thunderbird 152.0.0`