Re: Port 113 requests?

["Crist J . Clark" <cristjc () earthlink net>]

On Thu, Dec 06, 2001 at 01:51:33PM -0700, Slighter, Tim wrote:
> you really should try and specify that the rule "drops" instead of reject so
> that the potential intruder is not provided with any information about their
> attempted connection.

It's a trade. If you drop the auth attempts silently, you usually then
have to wait for the attempts to time out before whatever you did to
prompt the auth attempt can proceed. If you send a RST or
ICMP-unreachable, you don't have to wait for the time out.

In this case, it's someone's mail server getting the auth connection
attempt. Everyone knows where everybody else's mail servers are
(receiving hubs have MX records, senders are in the mail
headers). Sending RSTs on port 113 is just telling the world that you
don't want their auth requests; you are not really giving anything
away to an intruder.

> -----Original Message-----
> From: Chris Wilkes [mailto:cwilkes () ladro com]
> Sent: Thursday, December 06, 2001 1:05 PM
> To: incidents () securityfocus com
> Subject: Re: Port 113 requests?
>
>
> On Thu, Dec 06, 2001 at 01:51:57PM -0500, Michael Ward wrote:
> > I have been receiving the following entries at my firewall for since
> > noon US Eastern Time (-5:00) on 12/4/01.
> >
> > They have been coming every 15 minutes since then.  I notified the owner
> > of the IP's and he hasn't responded yet.
> >
> > 12/04/2001 11:59:30.336 - TCP connection dropped -
> > Source:mail.domain-i-edited.com, 40454, WAN -
> > Destination:my.mail.server, 113, LAN - 'Authentication' - Rule 32
>
> Its the SMTP AUTH protocol where a mail server tries to do an
> authenication check on who is sending it mail.  I've turned this off on
> my mail server as it really doesn't do any good.  I think some IRC
> servers use this feature.
>
> In my firewall I've setup this rule to handle these requests:
>       -p tcp --dport 113 -j REJECT --reject-with icmp-port-unreachable
>
> In short, nothing to be concerned about.
>
> Chris
>
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-- 
"It's always funny until someone gets hurt. Then it's hilarious."

Crist J. Clark                     |     cjclark () alum mit edu
                                   |     cjclark () jhu edu
http://people.freebsd.org/~cjc/    |     cjc () freebsd org

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