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Re: sshd logs and possible security violation



Hi Chris!

On Fri, 15 Feb 2002, Chris Evans wrote:

> I think this belongs on d.-user not the security or ssh lists.  
> 
> Thanks to people who helped point me to logcheck, I saw my first 
> attempted login from outside today.  At least, I'm pretty sure that's 
> what I saw but I am seeking some information about what gets logged 
> by sshd.

no expert here, but i think this is pam logging as pam is used for
authentification for ssh, login, su, sudo et al.

> What I see in auth.log is (consecutive lines):
> Feb 14 23:19:29 www sshd[438]: Did not receive ident string from
>    xxx.yy.zzz.uu (actual number removed in case!)
>        I think that's an usuccessful attempt to log in, am I right?
> 
> Feb 14 23:49:32 www sshd[242]: Generating new 768 bit RSA key.
> Feb 14 23:49:33 www sshd[242]: RSA key generation complete.
>       don't understand why sshd did that then, 30 minutes later

ssh generates new server RSA keys every once in a while. these RSA keys
are never written to disk and are generated from you (usually 1024 bit)
host key.

>       then the next lines are me testing what happens if I try to do 
> an illegal login:
> Feb 15 07:36:08 www su[1154]: + ??? root-www-data
> Feb 15 07:36:08 www PAM_unix[1154]: (su) session opened for user www-
> data by (uid=0)
>       which looks alarming but I was slung out by shell being
>       /usr/bin/false or by fact I didn't give right password

apache started by root?

> Feb 15 07:36:08 www su[1174]: + ??? root-nobody
> Feb 15 07:36:08 www PAM_unix[1174]: (su) session opened for user 
> nobody by (uid=0)
>       ditto

a daemon running as user nobody started from user root (could be via
inetd, xinetd, cron...)

> Feb 15 07:55:52 www sshd[1375]: Accepted password for xxxxxxx from
>    zzz.zzz.zzz.zzz port yyyy
> 
> That last line seems to be the logging of a successful login and it's 
> very reassuringly different from the one from someone else, from an 
> outside IP address.
> 
> I had a look in the ssh documentation (which points to various dead 
> URLs) but couldn't find anything detailed on logging messages.  I 
> don't think my programming is up to reading the source package to see 
> if that would tell me.  

as stated above i think you're looking at the wrong documentation. check
out the pam docs.

> I'm also under the impression that sshd generates new keys when 
> restarted and at intervals, does anyone know if that is right?

yes, that's correct (see man sshd: SSH protocol version 1 ).

yours martin
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