Fortunately, seems as if this is not as easy to exploit as it sounds. Patched dropbear to send SUCCESS instead of REQUEST and my servers throw `dispatch_protocol_error: type 52 seq 5 [preauth]`
As pronoiac has already said, libssh != OpenSSH, which is far more widely used. According to the footer on https://www.libssh.org/, projects using LibSSH include KDE's sftp implementation, X2Go, and... GitHub: "GitHub uses libssh in production to power its git SSH infrastructure, serving millions of requests daily." If the footer text is still accurate, that's probably the most concerning potential issue with this vuln, although it's also possible GitHub has mitigated this risk in other ways. It would be nice to see GitHub publish something about this, one way or the other.
I'll just note here that it is possible to disable password login to your account on a machine to which you do not have root access:
Use a combination of the "ssh_command" option in a authorized_keys to launch a bash session with a chosen environment variable set, and you set up your bashrc so that the lack of existence of this variable in the environment results in an immediate logout.
4 comments
[ 2.9 ms ] story [ 19.2 ms ] thread[1] https://packages.ubuntu.com/trusty/libssh-4 - I'm surprised I don't see reverse dependencies listed here.
[2] http://brewformulas.org/Libssh
Update: they recently tweeted confirming they were not at risk, https://twitter.com/GitHubSecurity/status/105231733337972326...
Use a combination of the "ssh_command" option in a authorized_keys to launch a bash session with a chosen environment variable set, and you set up your bashrc so that the lack of existence of this variable in the environment results in an immediate logout.