CVE-2021-36368 | Severity.io

Description

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.

Related CPE's

openbsd

openssh

Vulnerable

debian

debian_linux

References

https://bugzilla.mindrot.org/show_bug.cgi?id=3316

Issue TrackingThird Party Advisory

https://docs.ssh-mitm.at/trivialauth.html

Third Party Advisory

https://github.com/openssh/openssh-portable/pull/258