CVE-2025-6433: firefox: WebAuthn would allow a user to sign a challenge on a webpage with an invalid TLS certificate

Severity: Critical

CVSS Score: 9.8

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 affects Firefox < 140 and Thunderbird < 140.