[CentOS] Dovecot attack

Dag Wieers dag at wieers.com
Mon Aug 23 10:13:05 UTC 2010

On Mon, 23 Aug 2010, Timothy Murphy wrote:

> It seems there was some kind of attack against dovecot on my server
> (CentOS-5.5) with a hundred or so logwatch entries like:
> =========================================
> **Unmatched Entries**
> dovecot-auth: pam_succeed_if(dovecot:auth):
>  error retrieving information about user admin
> dovecot-auth: pam_succeed_if(dovecot:auth):
>  error retrieving information about user webmaster
> =========================================
> I googled for this, and it seems quite a common occurrence.
> Basically, I'm wondering whether this is best met
> at the dovecot level, or at my firewall?
> I'm running shorewall, and I see advice
> to impose a time-interval between successive attempts like these,
> but I'm not sure of the best way to do this?

I can recommend pam_shield for something like this. pam_shield is a 
generic solution for blocking unsuccessful login attempts. You can specify 
the number of failures within an interval, and after what grace time the 
entries are removed. I have been using it for years !

pam_shield by default works by null-routing offending IP addresses, but 
you can also make it add reject tools in iptables if you prefer this.

Since pam_shield works through pam, it is more efficient than anything 
that scans logfiles and it will work immediately (and not only after some 
rescan job). And the most important benefit, it works for any service in 

pam_shield is available from RPMforge and requires a minimum of 

Kind regards,
--   dag wieers,  dag at wieers.com,  http://dag.wieers.com/   --
[Any errors in spelling, tact or fact are transmission errors]

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