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I usually SSH into my home system remotely with no issues.
As of last night, when I attempt to log into the system with PuTTY, here's what happens: It prompts me for a user name and accepts it. It then prompts me for a password, and it then immediately aborts with the message:"Server unexpectedly closed network connection".
I checked /var/cache/apt/archives/ to see if my last upgrade included an ssh package. It did not.
/var/log/auth.log shows this message for each login attempt:
Sep 30 21:47:00 austin sshd: Accepted keyboard-interactive/pam for myusername from 18.104.22.168 port 29260 ssh2
Sep 30 21:47:00 austin sshd: (pam_unix) session opened for user myusername by (uid=0)
Sep 30 21:47:00 austin sshd: fatal: PAM: pam_setcred(): Critical error - immediate abort
Sep 30 21:47:00 austin sshd: (pam_unix) session closed for user myusername
I checked my backup CD that I so wisely made a month ago and compared the /etc/ssh/sshd_config files and they are the same.
From another post, i figured out that by default, ubuntu puts ALL:ALL in hosts.deny file. So typically, the server would not be able to take any incoming http/ssh connection. You might like to remove the entry for the server to be able to take connections. Alternatively, you can selectively allow IPs in /etc/hosts.allow file.
The most likelly thing is that some updated package replaced your hosts.deny, hosts.allow, hosts.equiv, and hosts files with the default versions (of which the hosts.deny is set to ALL:ALL) what you have to do is that when you update packages you need to verify which config files it's replacing.