[Dovecot] Authentication failure messages in logs

[Steffen Kaiser]

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On Sat, 16 Mar 2013, Nicolas Mora wrote:

> I'm currently running dovecot on a debian stable and every day, I see this 
> message dozens of time in my logs :

> Mar 16 11:27:57 hector dovecot-auth: pam_unix(dovecot:auth): authentication 
> failure; logname= uid=0 euid=0 tty=dovecot ruser=nicolas rhost=72.53.129.223 
> user=nicolas

> on the list archive, this message for example tells to comment out the pam 
> section.
> http://www.dovecot.org/list/dovecot/2008-July/031966.html
> Except that my authentication needs pam...
>
> Is there any way to solve this without migrating to virtual users ?

>  passdb:
>    driver: pam
>    args: dovecot

Well, you seem to use just one passdb. The article you are referring to 
says "the first try is always empty username and password so it slows down 
terribly every action.".

So to clarify your situation a bit:

1) Did you enabled auth_debug? If not, do so for a day or two.
2) Do you see in the logs, if more than one database is queried for one 
login process. If not, the article does not match your situation.
3) Is "nicolas" a valid user? Are all users with authentication failure 
valid ones?
4) When you login _yourself_ manually (not with a cached password in 
Thunderbird), do you see that log message, too? If you are unsure, if you 
can login without a cached password, try to ssh to your server, then

telnet localhost 143
1 login "username" "password"
2 logout

5) Did you considered, your server is under (slow) attack?

- -- 
Steffen Kaiser
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