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FreeBSD box, throws that error (from sshd) on every new connection. Doesn't appear to impact the functioning of the system, but is kind of annoying. Sounds like it's unhappy about something in the primes file, but I don't know what. Is there any way to fix it?

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Is this an old, unpatched install? Your sshd's prime moduli is 'broke', it's somewhat likely this is due to being hacked (though it could be a file system problem or similar). Check the users on the system, see if there are any new ones. Stop allowing logins via SSH, it would be trivial to recover passwords from people logging in. –  Chris S Oct 23 '12 at 17:23
    
It's a completely current install. No visible evidence of hacks, no unusual users, logs, code, etc. I believe it started throwing these errors immediately after an update. Could it have gotten broken during the update? –  Brian Knoblauch Oct 23 '12 at 18:03

2 Answers 2

up vote 0 down vote accepted

Looks like the moduli file got mangled during the upgrade diff. I copied the /etc/ssh/moduli file from another machine and the problem is solved.

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I saw the same error messages from openSSH 4.9p1 compiled on SunOS 4.1.4. The reason was a failed test in the function parse_prime in dh.c:

prime = strsep(&cp, " "); /* prime */
if (cp != NULL || *prime == '\0')
        goto fail;

cp != NULL failed for reasons unknown to me, so I boldly removed this test to get rid of the error.

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