Improper Authentication Affecting openssh package, versions *

Note: Versions mentioned in the description apply only to the upstream openssh package and not the openssh package as distributed by Debian. See How to fix? for Debian:11 relevant fixed versions and status.

An issue was discovered in OpenSSH before 8.9. If a client is using public-key authentication with agent forwarding but without -oLogLevel=verbose, and an attacker has silently modified the server to support the None authentication option, then the user cannot determine whether FIDO authentication is going to confirm that the user wishes to connect to that server, or that the user wishes to allow that server to connect to a different server on the user's behalf. NOTE: the vendor's position is "this is not an authentication bypass, since nothing is being bypassed.

• https://security-tracker.debian.org/tracker/CVE-2021-36368
• https://github.com/openssh/openssh-portable/pull/258
• https://docs.ssh-mitm.at/trivialauth.html
• https://bugzilla.mindrot.org/show_bug.cgi?id=3316
• https://www.openssh.com/security.html