Re: MailSweeper for SMTP Security Problem

[Hugo van der Kooij <hvdkooij () VANDERKOOIJ ORG>]

On Tue, 27 Mar 2001, Russ Hayward wrote:

> There appears to be vulnerability with Mail Sweeper for SMTP email by
> Content Technologies.
> (Tested on Version 4.19, others may be vulnerable)
>
> My test system is -
>
>     Windows NT 4 Service Pack 5
>     MailSweeper for SMTP version 4.1.9

Version number 4.1_9 is assumed here.

> I have two separate incoming and outgoing policies scenarios, I trust (!) my
> users and allow all
> internal users to send what they like (no restrictions) but restrict
> incoming emails with
> virus checks, text analysis, exe file checks etc.. etc..
>
> The Incoming scenario applies to this address list *@* --> *@mydomain.com
> and the Outgoing Scenario applies to *@mydomain.com --> *@*
>
> The SMTP relay restrictions ensure that only mail destined for the local
> domain are forwarded.
>
> The problem occurs when an attacker spoofs an email so the sender appears to
> be a user within my
> domain i.e. JoeBloggs () mydomain com and the recipient is the intended victim
> i.e. user () mydomain com
>
> MailSweeper will apply the OUTGOING scenario (i.e. nothing) and forwards the
> mail internally to the
> intended victim. This email could contain any content.

The problem here is not in the software but the configuration. Outgoing
mail should be restricted to the internal mailserver(s) and a properly
configured systems passes al the email relay tests.

I've installed about half a dozen systems with mailsweeper and none of
them allow relaying. All of them have been tested externally for all
variants of email relay including bangpath variants.

Some were tested by the ISP as well as one was installed in a rush to stop
an email relaying problem that is present in v3 of the MailSweeper for
SMTP product and can not be fixed in the configuration.

Hugo.

--
Hugo van der Kooij; Oranje Nassaustraat 16; 3155 VJ  Maasland
hvdkooij () vanderkooij org             http://hvdkooij.xs4all.nl/
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        Don't meddle in the affairs of sysadmins,
        for they are subtle and quick to anger.