Critical severity · published Jun 24, 2025
CVE-2025-6433
WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate
9.8
CVSS
0.3%
EPSS
No
On KEV
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:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FI
Firefox · Mozilla
before 140.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-6433
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-6433
Permissions Required
https://bugzilla.mozilla.org/show_bug.cgi?id=1954033
Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-51/
www.mozilla.org
https://www.mozilla.org/security/advisories/mfsa2025-54/
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