Question about SSH connection crash in v7.6p1

[Michael Fong]

Hi all,


We are experiencing a SSH connection drop problem with Ubuntu 18.04 /
OpenSSH 7.6p1 using our own SSH client.  (not open ssh client)

When the user mistakenly puts invalid user name and client connects to SSH
server with public/private key authentication, the connection crashes with
core dump during key authentication.

We came across this fix in OpenSSH 7.7 release note and this may look
related:

ssh-agent(1) <https://man.openbsd.org/ssh-agent.1>: Fix regression
introduced in 7.6 that caused ssh-agent
   to fatally exit if presented an invalid signature request message.


If someone could share some insight and be familiar with the above fix, it
would be great! Any help is appreciated!

The same scenario is not reproducible with various Ubuntu version and only
seen this error on Ubuntu 18.04 / OpenSSH 7.6p1

Ubuntu 16.04 with OpenSSH_7.2p2, OpenSSL 1.0.2g ---- PASSED
Ubuntu 18.04 with OpenSSH_7.6p1, OpenSSL 1.0.2n ---- FAILED
Ubuntu 20.04 with OpenSSH_8.2p1, OpenSSL 1.1.1f ---- PASSED


Thanks in advance!