4.27.9 ‘Misuses the session ID in SSH-2 PK auth’

Versions below 2.3 of OpenSSH require SSH-2 public-key authentication to be done slightly differently: the data to be signed by the client contains the session ID formatted in a different way. If public-key authentication mysteriously does not work but the Event Log (see section 3.1.3.1) thinks it has successfully sent a signature, it might be worth enabling the workaround for this bug to see if it helps.

If this bug is detected, PuTTY will sign data in the way OpenSSH expects. If this bug is enabled when talking to a correct server, SSH-2 public-key authentication will fail.

This is an SSH-2-specific bug.