--- -- Functions for the SSH-2 protocol. -- -- @author Sven Klemm -- @copyright Same as Nmap--See https://nmap.org/book/man-legal.html local base64 = require "base64" local string = require "string" local nmap = require "nmap" local stdnse = require "stdnse" local openssl = stdnse.silent_require "openssl" _ENV = stdnse.module("ssh2", stdnse.seeall) -- table holding transport layer functions transport = {} -- table of SSH-2 constants local SSH2 --- Retrieve the size of the packet that is being received -- and checks if it is fully received -- -- This function is very similar to the function generated -- with match.numbytes(num) function, except that this one -- will check for the number of bytes on-the-fly, based on -- the written on the SSH packet. -- -- @param buffer The receive buffer -- @return packet_length, packet_length or nil -- the return is similar to the lua function string:find() check_packet_length = function( buffer ) if #buffer < 4 then return nil end -- not enough data in buffer for int local packet_length, offset = string.unpack( ">I4", buffer ) assert(packet_length) if packet_length + 4 > buffer:len() then return nil end return packet_length+4, packet_length+4 end --- Receives a complete SSH packet, even if fragmented -- -- This function is an abstraction layer to deal with -- checking the packet size to know if there is any more -- data to receive. -- -- @param socket The socket used to receive the data -- @return status True or false -- @return packet The packet received transport.receive_packet = function( socket ) local status, packet = socket:receive_buf(check_packet_length, true) return status, packet end --- Pack a multiprecision integer for sending. -- @param bn openssl bignum. -- @return Packed multiprecision integer. transport.pack_mpint = openssl.bignum_bn2mpi or function( bn ) local bytes, packed bytes = bn:num_bytes() packed = bn:tobin() if bytes > 0 and bn:num_bits() % 8 == 0 then bytes = bytes + 1 packed = '\0' .. packed end return string.pack(">I4", bytes) .. packed end --- Build an SSH-2 packet. -- @param payload Payload of the packet. -- @return Packet to send on the wire. transport.build = function( payload ) local packet_length, padding_length padding_length = 8 - ( (payload:len() + 1 + 4 ) % 8 ) -- padding length must be at least 4 bytes and is a multiple -- of the cipher block size or 8 if padding_length < 4 then padding_length = padding_length + 8 end packet_length = payload:len() + padding_length + 1 return string.pack(">I4B", packet_length, padding_length) .. payload .. openssl.rand_pseudo_bytes(padding_length) end --- Extract the payload from a received SSH-2 packet. -- @param packet Received SSH-2 packet. -- @return Payload of the SSH-2 packet. transport.payload = function( packet ) local packet_length, padding_length, offset = string.unpack( ">I4B", packet ) assert(packet_length and padding_length) local payload_length = packet_length - padding_length - 1 if packet_length ~= (#packet - 4) then stdnse.debug1("SSH-2 packet doesn't match length: payload_length is %d but total length is only %d.", packet_length, #packet - 4) return nil end local payload = string.sub(packet, offset, offset + payload_length) return payload end --- Build a kexdh_init packet. transport.kexdh_init = function( e ) return string.pack( "B", SSH2.SSH_MSG_KEXDH_INIT) .. transport.pack_mpint( e ) end --- Build a kexdh_gex_init packet. transport.kexdh_gex_init = function( e ) return string.pack( "B", SSH2.SSH_MSG_KEX_DH_GEX_INIT) .. transport.pack_mpint( e ) end --- Build a kex_init packet. transport.kex_init = function( options ) options = options or {} local cookie = options['cookie'] or openssl.rand_bytes( 16 ) local kex_algorithms = options['kex_algorithms'] or "diffie-hellman-group1-sha1" local host_key_algorithms = options['host_key_algorithms'] or "ssh-dss,ssh-rsa" local encryption_algorithms = options['encryption_algorithms'] or "aes128-cbc,3des-cbc,blowfish-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr" local mac_algorithms = options['mac_algorithms'] or "hmac-md5,hmac-sha1,hmac-ripemd160" local compression_algorithms = options['compression_algorithms'] or "none" local languages = options['languages'] or "" local payload = string.pack( "B", SSH2.SSH_MSG_KEXINIT) .. cookie .. string.pack( ">s4s4 s4s4 s4s4 s4s4 s4s4 BI4", kex_algorithms, host_key_algorithms, encryption_algorithms, encryption_algorithms, mac_algorithms, mac_algorithms, compression_algorithms, compression_algorithms, languages, languages, 0, 0 ) return payload end --- Parse a kexinit package. -- -- Returns an empty table in case of an error transport.parse_kex_init = function( payload ) local parsed = {} -- check for proper msg code local msg_code, offset = string.unpack( "B", payload ) if msg_code ~= SSH2.SSH_MSG_KEXINIT then return {} end parsed.cookie, offset = string.unpack( "c16", payload, offset ) local fields = {'kex_algorithms','server_host_key_algorithms', 'encryption_algorithms_client_to_server','encryption_algorithms_server_to_client', 'mac_algorithms_client_to_server','mac_algorithms_server_to_client', 'compression_algorithms_client_to_server','compression_algorithms_server_to_client', 'languages_client_to_server','languages_server_to_client'} for _, fieldname in pairs( fields ) do parsed[fieldname], offset = string.unpack( ">s4", payload, offset ) end return parsed end --- Fetch an SSH-2 host key. -- @param host Nmap host table. -- @param port Nmap port table. -- @param key_type key type to fetch. -- @return A table with the following fields: key, -- key_type, fp_input, bits, -- full_key, algorithm, and fingerprint. fetch_host_key = function( host, port, key_type ) local socket = nmap.new_socket() local status -- oakley group 2 prime taken from rfc 2409 local prime2 = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1\z 29024E088A67CC74020BBEA63B139B22514A08798E3404DD\z EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245\z E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED\z EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381\z FFFFFFFFFFFFFFFF" -- oakley group 14 prime taken from rfc 3526 local prime14 = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1\z 29024E088A67CC74020BBEA63B139B22514A08798E3404DD\z EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245\z E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED\z EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D\z C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F\z 83655D23DCA3AD961C62F356208552BB9ED529077096966D\z 670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B\z E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9\z DE2BCBF6955817183995497CEA956AE515D2261898FA0510\z 15728E5A8AACAA68FFFFFFFFFFFFFFFF" -- oakley group 16 prime taken from rfc 3526 local prime16 = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD1\z 29024E088A67CC74020BBEA63B139B22514A08798E3404DD\z EF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245\z E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED\z EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3D\z C2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F\z 83655D23DCA3AD961C62F356208552BB9ED529077096966D\z 670C354E4ABC9804F1746C08CA18217C32905E462E36CE3B\z E39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9\z DE2BCBF6955817183995497CEA956AE515D2261898FA0510\z 15728E5A8AAAC42DAD33170D04507A33A85521ABDF1CBA64\z ECFB850458DBEF0A8AEA71575D060C7DB3970F85A6E1E4C7\z ABF5AE8CDB0933D71E8C94E04A25619DCEE3D2261AD2EE6B\z F12FFA06D98A0864D87602733EC86A64521F2B18177B200C\z BBE117577A615D6C770988C0BAD946E208E24FA074E5AB31\z 43DB5BFCE0FD108E4B82D120A92108011A723C12A787E6D7\z 88719A10BDBA5B2699C327186AF4E23C1A946834B6150BDA\z 2583E9CA2AD44CE8DBBBC2DB04DE8EF92E8EFC141FBECAA6\z 287C59474E6BC05D99B2964FA090C3A2233BA186515BE7ED\z 1F612970CEE2D7AFB81BDD762170481CD0069127D5B05AA9\z 93B4EA988D8FDDC186FFB7DC90A6C08F4DF435C934063199\z FFFFFFFFFFFFFFFF" status = socket:connect(host, port) if not status then return end -- fetch banner status = socket:receive_lines(1) if not status then socket:close(); return end -- send our banner status = socket:send("SSH-2.0-Nmap-SSH2-Hostkey\r\n") if not status then socket:close(); return end local packet = transport.build( transport.kex_init( { host_key_algorithms=key_type, kex_algorithms="diffie-hellman-group1-sha1,\z diffie-hellman-group14-sha1,\z diffie-hellman-group14-sha256,\z diffie-hellman-group16-sha512,\z diffie-hellman-group-exchange-sha1,\z diffie-hellman-group-exchange-sha256", } ) ) status = socket:send( packet ) if not status then socket:close(); return end local kex_init status, kex_init = transport.receive_packet( socket ) if not status then socket:close(); return end kex_init = transport.parse_kex_init( transport.payload( kex_init ) ) if not tostring(kex_init.server_host_key_algorithms):find( key_type, 1, true ) then -- server does not support host key type stdnse.debug2("Hostkey type '%s' not supported by server.", key_type ) return end local kex_algs = tostring( kex_init.kex_algorithms ) local kexdh_gex_used = false local prime, q, gen -- NB: For each KEX prefix used here, make sure that all corresponding -- algorithms are listed in the transport.kex_init() call above. -- Otherwise this code might proceed with an incorrect KEX. if kex_algs:find("diffie-hellman-group1-", 1, true) then prime = prime2 q = 1024 gen = "2" elseif kex_algs:find("diffie-hellman-group14-", 1, true) then prime = prime14 q = 2048 gen = "2" elseif kex_algs:find("diffie-hellman-group16-", 1, true) then prime = prime16 q = 4096 gen = "2" elseif kex_algs:find("diffie-hellman-group-exchange-", 1, true) then local min, n, max min = 1024 n = 1024 max = 8192 packet = transport.build( string.pack( ">BI4I4I4", SSH2.SSH_MSG_KEX_DH_GEX_REQUEST, min, n, max ) ) status = socket:send( packet ) if not status then socket:close(); return end local gex_reply status, gex_reply = transport.receive_packet( socket ) if not status then socket:close(); return end gex_reply = transport.payload( gex_reply ) -- check for proper msg code if gex_reply:byte(1) ~= SSH2.SSH_MSG_KEX_DH_GEX_GROUP then socket:close() return end local _ _, prime, gen = string.unpack( ">Bs4s4", gex_reply ) prime = openssl.bignum_bin2bn( prime ):tohex() q = 1024 gen = openssl.bignum_bin2bn( gen ):todec() kexdh_gex_used = true else stdnse.debug2("No shared KEX methods supported by server") return end local e, g, x, p -- e = g^x mod p g = openssl.bignum_dec2bn( gen ) p = openssl.bignum_hex2bn( prime ) x = openssl.bignum_pseudo_rand( q ) e = openssl.bignum_mod_exp( g, x, p ) -- if kexdh_gex_used then -- e = openssl.bignum_pseudo_rand( 1024 ) -- end local payload if kexdh_gex_used == true then payload = transport.kexdh_gex_init( e ) else payload = transport.kexdh_init( e ) end packet = transport.build( payload ) status = socket:send( packet ) if not status then socket:close(); return end local kexdh_reply status, kexdh_reply = transport.receive_packet( socket ) if not status then socket:close(); return end kexdh_reply = transport.payload( kexdh_reply ) -- check for proper msg code local msg_code = kexdh_reply:byte(1) if ( kexdh_gex_used == true and msg_code ~= SSH2.SSH_MSG_KEX_DH_GEX_REPLY ) or ( kexdh_gex_used == false and msg_code ~= SSH2.SSH_MSG_KEXDH_REPLY ) then socket:close() return end local bits, algorithm local _, public_host_key = string.unpack( ">Bs4", kexdh_reply ) if key_type == 'ssh-dss' then algorithm = "DSA" local _, p = string.unpack( ">s4s4", public_host_key ) bits = openssl.bignum_bin2bn( p ):num_bits() elseif key_type == 'ssh-rsa' then algorithm = "RSA" local _, _, n = string.unpack( ">s4s4s4", public_host_key ) bits = openssl.bignum_bin2bn( n ):num_bits() elseif key_type == 'ecdsa-sha2-nistp256' then algorithm = "ECDSA" bits = "256" elseif key_type == 'ecdsa-sha2-nistp384' then algorithm = "ECDSA" bits = "384" elseif key_type == 'ecdsa-sha2-nistp521' then algorithm = "ECDSA" bits = "521" elseif key_type == 'ssh-ed25519' then algorithm = "ED25519" bits = "256" else stdnse.debug1("Unsupported key type: %s", key_type ) end socket:close() return { key=base64.enc(public_host_key), key_type=key_type, fp_input=public_host_key, bits=bits, full_key=('%s %s'):format(key_type,base64.enc(public_host_key)), algorithm=algorithm, fingerprint=openssl.md5(public_host_key), fp_sha256=openssl.digest("sha256",public_host_key)} end -- constants SSH2 = { SSH_MSG_DISCONNECT = 1, SSH_MSG_IGNORE = 2, SSH_MSG_UNIMPLEMENTED = 3, SSH_MSG_DEBUG = 4, SSH_MSG_SERVICE_REQUEST = 5, SSH_MSG_SERVICE_ACCEPT = 6, SSH_MSG_KEXINIT = 20, SSH_MSG_NEWKEYS = 21, SSH_MSG_KEXDH_INIT = 30, SSH_MSG_KEXDH_REPLY = 31, SSH_MSG_KEX_DH_GEX_REQUEST_OLD = 30, SSH_MSG_KEX_DH_GEX_REQUEST = 34, SSH_MSG_KEX_DH_GEX_GROUP = 31, SSH_MSG_KEX_DH_GEX_INIT = 32, SSH_MSG_KEX_DH_GEX_REPLY = 33, } local unittest = require "unittest" if not unittest.testing() then return _ENV end test_suite = unittest.TestSuite:new() local mpints = { {"0", "\x00\x00\x00\x00"}, {"9a378f9b2e332a7", "\x00\x00\x00\x08\x09\xa3\x78\xf9\xb2\xe3\x32\xa7"}, {"80", "\x00\x00\x00\x02\x00\x80"}, --[[ RFC 4251 says negative numbers are 2's complement, but OpenSSL doesn't do that {"-1234", "\x00\x00\x00\x02\xed\xcc"}, {"-deadbeef", "\x00\x00\x00\x05\xff\x21\x52\x41\x11"}, ]]-- } for _, t in ipairs(mpints) do local bn = openssl.bignum_hex2bn(t[1]) test_suite:add_test(unittest.equal(transport.pack_mpint(bn), t[2]), ("pack mpint 0x%s"):format(t[1])) end return _ENV;