---
id: CVE-2026-100809
title: Same-origin policy bypass in the DevTools component
summary: >-
  Same-origin policy bypass in the DevTools component. This vulnerability was
  fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox
  157.
severity: high
cvss: 8.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N'
cwe:
  - CWE-346
vendor: mozilla
product: firefox
affected:
  - firefox < 153.4.0
  - 'firefox >= 154.0.0, < 157.0.0'
  - thunderbird < 153.4.0
  - 'thunderbird >= 154.0, < 157.0'
patched:
  - firefox 157.0.0
  - thunderbird 157.0
published: '2026-09-29'
updated: '2026-10-05'
sourceUpdated: '2026-10-05T14:30:57.960'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100809'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=2063658'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-100/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-101/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-103/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2026-97/'
    label: security@mozilla.org
tags:
  - nvd
  - cve.org
epss: 0.00153
epssPercentile: 0.04351
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-01T15:30:21.266547Z'
ingestedAt: '2026-09-29T13:34:31.672Z'
---

## Overview

Same-origin policy bypass in the DevTools component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

## Affected

- `firefox < 153.4.0`
- `firefox >= 154.0.0, < 157.0.0`
- `thunderbird < 153.4.0`
- `thunderbird >= 154.0, < 157.0`

## Remediation

Upgrade past the affected range:

- `firefox 157.0.0`
- `thunderbird 157.0`