---
id: CVE-2025-6434
title: >-
  The exception page for the HTTPS-Only feature, displayed when a website is
  opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an
  attacker to trick a user into granting an exception and loading a webpage over
  HTTP
summary: >-
  The exception page for the HTTPS-Only feature, displayed when a website is
  opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an
  attacker to trick a user into granting an exception and loading a webpage over
  HTTP. T…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N'
cwe:
  - CWE-1021
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-2025-6434'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1955182'
    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: 0.00283
epssPercentile: 0.1873
ingestedAt: '2026-09-30T18:17:24.445Z'
---

## Overview

The exception page for the HTTPS-Only feature, displayed when a website is opened via HTTP, lacked an anti-clickjacking delay, potentially allowing an attacker to trick a user into granting an exception and loading a webpage over HTTP. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

## Affected

- `firefox < 140.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.0`