WebAuthn Challenge Vulnerability in Mozilla Firefox
CVE-2025-6433

9.8CRITICAL

Key Information:

Vendor

Mozilla
Status
Firefox
Thunderbird
Vendor
CVE Published:
24 June 2025

What is CVE-2025-6433?

An issue exists in Mozilla Firefox where users visiting a webpage with an invalid TLS certificate may be prompted to complete a WebAuthn challenge. This occurs after users grant an exception for the invalid certificate, effectively allowing bypass of established security protocols as stated in the WebAuthn specification, which mandates a secure transport and unbroken connection during authentication procedures. Consequently, this vulnerability raises significant security concerns regarding improper handling of certificate errors and user authentication.

Affected Version(s)

Firefox < 140

Thunderbird < 140

References

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

CVSS V3.1

Score:
9.8
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Simon
.
CVE-2025-6433 : WebAuthn Challenge Vulnerability in Mozilla Firefox