CVE-2025-6433

Name: CVE-2025-6433
Creator: NVD / NIST
Published: 2025-06-24T13:15:24.327+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 0.24%

Last modified Jun 17, 2026

CVE-2025-6433 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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". EPSS estimates a 0.24% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.24%

15.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-295

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 140.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1954033Permissions Required
https://www.mozilla.org/security/advisories/mfsa2025-51/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-54/

Timeline

Published: Jun 24, 2025
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2025-6433?

How severe is CVE-2025-6433?

CVE-2025-6433 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.24% probability of exploitation in the next 30 days.

How do I fix CVE-2025-6433?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-6433?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST