---
id: CVE-2025-6427
title: >-
  An attacker was able to bypass the `connect-src` directive of a Content
  Security Policy by manipulating subdocuments
summary: >-
  An attacker was able to bypass the `connect-src` directive of a Content
  Security Policy by manipulating subdocuments. This would have also hidden the
  connections from the Network tab in Devtools. This vulnerability was fixed in
  Firefox 1…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-693
vendor: mozilla
product: firefox
affected:
  - firefox < 140.0
patched:
  - firefox 140.0
published: '2025-06-24'
updated: '2026-09-30'
sourceUpdated: '2026-09-30T18:10:00.190'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-6427'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1966927'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-51/'
    label: security@mozilla.org
  - url: 'https://www.mozilla.org/security/advisories/mfsa2025-54/'
    label: security@mozilla.org
tags:
  - nvd
epss: 0.00368
epssPercentile: 0.28268
ingestedAt: '2026-09-30T18:17:24.443Z'
---

## Overview

An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

## Affected

- `firefox < 140.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.0`