openssh bugs - May 2018 - [Bug 2867] New: No HostKeyAlgorithm is offered by sshd if "rsa-sha2-512" algorithm is forced.

https://bugzilla.mindrot.org/show_bug.cgi?id=2867

            Bug ID: 2867
           Summary: No HostKeyAlgorithm is offered by sshd if
                    "rsa-sha2-512" algorithm is forced.
           Product: Portable OpenSSH
           Version: 7.7p1
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: sshd
          Assignee: unassigned-bugs at mindrot.org
          Reporter: xavier.garriga at gmail.com

If 'rsa-sha2-512' Host Key Algorithm is the only algorithm in
sshd_coonfig or sshd is forced to start using only 'rsa-sha2-512' as
Host Key Algorithm no algorithm is offered to client during
negotiation.

Start server with:
sshd -oHostKeyAlgorithms="rsa-sha2-512"

When client tries to connect no HostKeyAlgorithm is offered.

debug2: peer server KEXINIT proposal
debug2: KEX algorithms:
curve25519-sha256,curve25519-sha256 at
libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: 
debug2: ciphers ctos: aes256-ctr,aes192-ctr,aes128-ctr
debug2: ciphers stoc: aes256-ctr,aes192-ctr,aes128-ctr

and connection is not established.

Same problem with "rsa-sha2-256".

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https://bugzilla.mindrot.org/show_bug.cgi?id=2867

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |djm at mindrot.org
             Blocks|                            |2852

--- Comment #1 from Damien Miller <djm at mindrot.org> ---
There's a fix for this in the patch at
https://bugzilla.mindrot.org/show_bug.cgi?id=2799


Referenced Bugs:

https://bugzilla.mindrot.org/show_bug.cgi?id=2852
[Bug 2852] Tracking bug for OpenSSH 7.8 release
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https://bugzilla.mindrot.org/show_bug.cgi?id=2867

Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Damien Miller <djm at mindrot.org> ---
This was fixed by the following commit and will be in OpenSSH 7.8:


commit 4ba0d54794814ec0de1ec87987d0c3b89379b436
Author: djm at openbsd.org <djm at openbsd.org>
Date:   Tue Jul 3 11:39:54 2018 +0000

    upstream: Improve strictness and control over RSA-SHA2 signature

    In ssh, when an agent fails to return a RSA-SHA2 signature when
    requested and falls back to RSA-SHA1 instead, retry the signature
to
    ensure that the public key algorithm sent in the SSH_MSG_USERAUTH
    matches the one in the signature itself.

    In sshd, strictly enforce that the public key algorithm sent in the
    SSH_MSG_USERAUTH message matches what appears in the signature.

    Make the sshd_config PubkeyAcceptedKeyTypes and
    HostbasedAcceptedKeyTypes options control accepted signature
algorithms
    (previously they selected supported key types). This allows these
    options to ban RSA-SHA1 in favour of RSA-SHA2.

    Add new signature algorithms "rsa-sha2-256-cert-v01 at
openssh.com"
and
    "rsa-sha2-512-cert-v01 at openssh.com" to force use of RSA-SHA2
signatures
    with certificate keys.

    feedback and ok markus@

    OpenBSD-Commit-ID: c6e9f6d45eed8962ad502d315d7eaef32c419dde

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Damien Miller <djm at mindrot.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

--- Comment #3 from Damien Miller <djm at mindrot.org> ---
Close RESOLVED bugs with the release of openssh-8.0

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