sshd logins without a source

[BH <lists () blackhat bz>]

Hi,

I am taking a look at a few different servers that have been rooted at
around the same time. At the time of the compromise I can see in each
servers sshd logs an entry like the following:

Sep 22 12:57:14 test-vm sshd[25002]: pam_unix(sshd:session): session
opened for user root by (uid=0)
Sep 22 12:57:32 test-vm sshd[25002]: pam_unix(sshd:session): session
closed for user root

Each of the servers has the same sort of entry in the log that match
with the time that extra processes were being executed. Having a look at
all other available logs (that were logged remotely) I can't see
anything else that relates to the same event. To me it seems odd that
there is no IP address corresponding with the login, I can't seem to
reproduce that on my test servers. I also can't see the authentication
method used as that isn't logged. Has anyone seen this before and know
how this is done?

Thanks

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