CVE-2025-6433 — Improper Certificate Validation in Mozilla Firefox

CWE-295 — Improper Certificate Validation9 documents8 sources
Severity
9.8CRITICALNVD
EPSS
0.1%
top 80.44%
CISA KEV
Not in KEV
Exploit
No known exploits
Affected products
2
Mozilla FirefoxMozilla Thunderbird
Timeline
PublishedJun 24
Latest updateFeb 2

Description

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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitability: 3.9 | Impact: 5.9

Affected Packages2 packages

▶NVDmozilla/firefox< 140.0
▶Ubuntumozilla/thunderbird< 1:140.7.1+build1-0ubuntu0.22.04.1

🔴Vulnerability Details

3
GHSA
GHSA-7f3m-mqm5-5x2c: 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 u↗2025-06-26
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OSV
CVE-2025-6433: 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 u↗2025-06-24
▶
CVEList
WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate↗2025-06-24
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📋Vendor Advisories

5
Ubuntu
Thunderbird vulnerabilities↗2026-02-02
▶
Red Hat
firefox: WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate↗2025-06-24
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Debian
CVE-2025-6433: firefox - If a user visited a webpage with an invalid TLS certificate, and granted an exce...↗2025
▶
Mozilla
Mozilla Foundation Security Advisory 2025-54: CVE-2025-6433↗
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Mozilla
Mozilla Foundation Security Advisory 2025-51: CVE-2025-6433↗
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CVE-2025-6433 — Improper Certificate Validation | cvebase