---
id: CVE-2025-6433
title: >-
  If a user visited a webpage with an invalid TLS certificate, and granted an
  exception, the webpage was able to provide a WebAuthn challenge that the user
  would be prompted to complete
summary: >-
  If a user visited a webpage with an invalid TLS certificate, and granted an
  exception, the webpage was able to provide a WebAuthn challenge that the user
  would be prompted to complete.  This is in violation of the WebAuthN spec
  which req…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-295
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-2025-6433'
references:
  - url: 'https://bugzilla.mozilla.org/show_bug.cgi?id=1954033'
    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: 0.00297
epssPercentile: 0.2024
ingestedAt: '2026-09-30T18:17:24.445Z'
---

## Overview

If a user visited a webpage with an invalid TLS certificate, and granted an exception, the webpage was able to provide a WebAuthn challenge that the user would be prompted to complete.  This is in violation of the WebAuthN spec which requires "a secure transport established without errors". This vulnerability was fixed in Firefox 140 and Thunderbird 140.

## Affected

- `firefox < 140.0`

## Remediation

Upgrade past the affected range:

- `firefox 140.0`