Rule:

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Sid:

1450

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Summary:
This event is generated when an attempt is made to send a malformed
request to an SMTP server which may cause a Denial of Service.

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Impact:
Denial of Service (DoS)

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Detailed Information:
The SMTP standard command "EXPN" is provided by servers to help find
user e-mail accounts.

A malformed request to certain versions of Vintra MailServer can cause a
DoS against that server.
 
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Affected Systems:

Vixar MailServer for Windows

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Attack Scenarios:
The attacker needs to connect to a vulnerable server and issue the
following commands.

>telnet victim.foo.com 25
>helo victim
>mail from:doctor
>rcpt to:evil
>expn *@

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Ease of Attack:

Simple. No exploit software required.

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False Positives:

None known.

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False Negatives:

None known.

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Corrective Action:

Disable the EXPN command on the SMTP server.

Upgrade to the latest non-affected version of the software

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Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>
Extra information from Nawapong Nakjang (tony@ksc.net, tonie@thai.com)

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Additional References:

NT Bugtraq:
http://marc.theaimsgroup.com/?l=ntbugtraq&m=90222454131610&w=2

Command Reference:
http://www.ntmail.co.uk/kb.htm?q=980

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