Or logic for handling SSH host keys when the port isn't 22 is currently broken and has been since bug 4557. The logic for OpenSSH is as follows: 1. If there are *any* keys for host:port, then use only those (including complaining if they don't match) 2. If there is a matching key for host:22, then silently proceed 3. Handle as a new host, prompting the user The idea here probably being that any non-standard port is probably the standard SSH server with a different port for firewall reasons. However our logic ended up being: 1. If there are *no* keys for host:port, handle as a new host, prompting the user 2. If there is a matching key for host:22, then silently proceed 3. Handle as a changed host, prompting the user This causes two problems: a. We get extra warnings for the user for the scenario of the standard SSH server on non-standard port b. A mild security issue as the owner of the :22 server can silently MITM servers on other ports. I say "mild" because the attacker would need to be able to control port 22, which means they are root and can likely do other attacks anyway. The proper behaviour also suffers from MITM issues on the initial connection instead.
It's actually even more broken than that. We just do the same check again (i.e. with the non-standard port, not port 22). So this has obviously never worked and was never actually tested.
Works better now. Tester should make sure our logic now follows the one in OpenSSH.
This works better now, I tested the following cases Case 1: No known hosts, connecting to port 22 Case 2: Known host:22, connecting to port 22 Case 3: Known host:22, connecting to non-standard port e.g. port 33333 Case 4: Known host:22 *CORRECT* key saved, and known host:33333 with *WRONG* key saved, connecting to host:33333 Case 5: Known host:33333, connecting to port 22 Case 6: Known host:33333, connecting to port 44444 And the results are show in the table bellow. | | Case 1 | Case 2 | Case 3 | Case 4 | Case 5 | Case 6 | |-------------------+--------+--------+--------+--------+--------+--------| | tl-4.12 | o | ✓ | o | x | o | o | | Nigtly build 6711 | o | ✓ | ✓* | x | o | o | | OpenSSH 8.2 | o | ✓ | ✓ | x | o | o | Legend: ✓ Silently moves on o Promt user, handle as new host x Wrong key, WARNING! * Adds [host]:33333 to known_hosts (As noted on bug 7536)
