[SSHD-1118] Unable to connect with Fedora 33 which has dropped ssh-rsa from PubkeyAcceptedKeyTypes

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Information Provided
• Affects Version/s: 2.4.0
• External issue URL: https://bugs.chromium.org/p/gerrit/issues/detail?id=13930
• Assignee: Unassigned
• Reporter: Ian Wienand
• Created: 12/Jan/21 22:52
• Updated: 02/Apr/21 06:35
• Resolved: 02/Apr/21 06:35

Description

This problem was noted with Gerrit using a 2.4.0 mina sshd server [1] after a recent upgrade.  Some users using Fedora 33 started being not able to log in.

It turns out that Fedora >=33 has dropped rsa-ssh from it's default PubkeyAcceptedKeyTypes in /etc/crypto-policies/back-ends/openssh.config.  You either have to modify your policy globally to "legacy" with "update-crypto-policies" or manually set PubkeyAcceptedKeyTypes=ssh-rsa for failing servers.

I understand that server-sig-algs support isn't fully implemented in mina sshd as yet, so the client will not be seeing the negotiation list.

However, it seems rsa-sha2-256/512 are supported?  It seems like forcing this with ssh -oPubkeyAcceptedKeyTypes=rsa-sha2-512 should work, but it does not (see related gerrit bug)?

I can provide ssh connect logs, etc. if it will help; at this point I think it's mostly about understanding Fedora's change and any mina limitations so we can find the best solution for users.  Although Fedora 33 users are obviously a small minority now, it probably flags something other distros will take up sooner or later.

 

Thanks!

 

 [1] https://bugs.chromium.org/p/gerrit/issues/detail?id=13930

Issue Links

• is fixed by: SSHD-1141 Implement server-sig-algs