possible SMTP attack

[Pedro Fernandes Macedo]

Olga wrote:

>Hi,
>
>I got this message in the logwatch sent to root:
>
>
>Client quit before communicating:
>    222.183.141.253 : 1 Time(s)
>
>**Unmatched Entries**
>   [222.183.141.253]: possible SMTP attack: command=AUTH, count=6: 1 Time(s)
>
>
>What does it mean? How can I protect my server against SMTP attacks?
>
>Thank you.
>
>Olga
>
>
>  
>
Besides firewalling this IP, nothing much..... Dont know what kind of 
attack is it , but maybe limiting AUTH to secure channels can stop it 
(if the attacker dont have tools that support TLS). In postfix you have 
the option to only allow the use of the AUTH command if TLS is being 
used. Dont know if sendmail can do the same thing though...
The only downside (which isnt in fact a downside) is that your users 
will have to use TLS , but this way you gain in terms of security... 
They'll have a bit of headache if your certificates are self-signed , 
but that's easy to overcome that...

--
Pedro Macedo