authentik is an open-source identity provider. A vulnerability that exists in versions prior to 2024.8.3 and 2024.6.5 allows bypassing password login by adding X-Forwarded-For header with an unparsable IP address, e.g. a. This results in a possibility of logging into any account with a known login or email address.

The vulnerability requires the authentik instance to trust X-Forwarded-For header provided by the attacker, thus it is not reproducible from external hosts on a properly configured environment. The issue occurs due to the password stage having a policy bound to it, which skips the password stage if the Identification stage is setup to also contain a password stage. Due to the invalid X-Forwarded-For header, which does not get validated to be an IP Address early enough, the exception happens later and the policy fails.

The default blueprint doesn't correctly set failure_result to True on the policy binding meaning that due to this exception the policy returns false and the password stage is skipped. Versions 2024.8.3 and 2024.6.5 fix this issue.