Updated the description - specifically, this appears to affect certificate authentication and be related to rsa- sha2-512-cert-...@openssh.com and rsa-sha2-256-cert-...@openssh.com which are present in 7.8 server, but not earlier versions (nor are valid to add to the configuration manually).
** Summary changed: - Unable to connect with openssh 7.8 client + Unable to connect with openssh 7.8 client and certificates ** Description changed: - Users are unable to connect to Ubuntu when using openssh client 7.8. We - have seen this with both xenial and bionic, but this affects connecting - to ANY host running openssh server <7.8. + Users are unable to connect to Ubuntu when using openssh client 7.8 and + certificates. We have seen this with both xenial and bionic, but this + affects connecting to ANY host running openssh server <7.8. + + It appears to be specific to using certificate authentication. The only known recourse at this time is either downgrade clients to 7.7 or a previous version of openssh, or create new keys/certificates with a different alg that is acceptable for both the older server and newer client. The error message via ssh -vvv is: debug1: Next authentication method: publickey debug1: Offering public key: RSA SHA256:REDACTED debug1: send_pubkey_test: no mutual signature algorithm + + When comparing the list returned from a 7.6 server and a 7.8 server via + "ssh -Q key", we find that 7.8 returns rsa-sha2-512-cert-...@openssh.com + and rsa-sha2-256-cert-...@openssh.com which are not present (or valid) + for the earlier version server. It appears that the change noted here in the release notes[1] for 7.8 is related: * sshd(8): the semantics of PubkeyAcceptedKeyTypes and the similar HostbasedAcceptedKeyTypes options have changed. These now specify signature algorithms that are accepted for their respective authentication mechanism, where previously they specified accepted key types. This distinction matters when using the RSA/SHA2 signature algorithms "rsa-sha2-256", "rsa-sha2-512" and their certificate counterparts. Configurations that override these options but omit these algorithm names may cause unexpected authentication failures (no action is required for configurations that accept the default for these options). + This is also affecting other Linux distributions as well: https://bugzilla.redhat.com/show_bug.cgi?id=1623929 https://bugs.archlinux.org/task/59838 [1] https://www.openssh.com/txt/release-7.8 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1790963 Title: Unable to connect with openssh 7.8 client and certificates To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1790963/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
