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ssh2.lua
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--- -- Functions for the SSH-2 protocol. -- -- @author Sven Klemm <sven@c3d2.de> -- @copyright Same as Nmap--See http://nmap.org/book/man-legal.html local base64 = require "base64" local bin = require "bin" local nmap = require "nmap" local openssl = require "openssl" local stdnse = require "stdnse" local string = require "string" _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 offset, packet_length = bin.unpack( ">I", 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 <code>openssl</code> bignum. -- @return Packed multiprecision integer. transport.pack_mpint = function( bn ) local bytes, packed bytes = bn:num_bytes() packed = bn:tobin() if bytes % 8 == 0 then bytes = bytes + 1 packed = string.char(0) .. packed end return bin.pack( ">IA", 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 ) packet_length = payload:len() + padding_length + 1 return bin.pack( ">IcAA", 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, payload_length, payload, offset offset, packet_length = bin.unpack( ">I", packet ) packet = packet:sub(offset); offset, padding_length = bin.unpack( ">c", packet ) assert(packet_length and padding_length) payload_length = packet_length - padding_length - 1 if packet_length ~= packet:len() then stdnse.print_debug("SSH-2 packet doesn't match length: payload_length is %d but total length is only %d.", packet_length, packet:len()) return nil end offset, payload = bin.unpack( ">A" .. payload_length, packet, offset ) return payload end --- Build a <code>kexdh_init</code> packet. transport.kexdh_init = function( e ) return bin.pack( ">cA", SSH2.SSH_MSG_KEXDH_INIT, transport.pack_mpint( e ) ) end --- Build a <code>kex_init</code> 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 = bin.pack( ">cAaa", SSH2.SSH_MSG_KEXINIT, cookie, kex_algorithms, host_key_algorithms ) payload = payload .. bin.pack( ">aa", encryption_algorithms, encryption_algorithms ) payload = payload .. bin.pack( ">aa", mac_algorithms, mac_algorithms ) payload = payload .. bin.pack( ">aa", compression_algorithms, compression_algorithms ) payload = payload .. bin.pack( ">aa", languages, languages ) payload = payload .. bin.pack( ">cI", 0, 0 ) return payload end --- Parse a <code>kexinit</code> package. -- -- Returns an empty table in case of an error transport.parse_kex_init = function( payload ) local _, offset, msg_code, parsed, fields, fieldname parsed = {} -- check for proper msg code offset, msg_code = bin.unpack( ">c", payload ) if msg_code ~= SSH2.SSH_MSG_KEXINIT then return {} end offset, parsed.cookie = bin.unpack( ">A16", payload, offset ) 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 offset, parsed[fieldname] = bin.unpack( ">a", 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: <code>key</code>, -- <code>key_type</code>, <code>fp_input</code>, <code>bits</code>, -- <code>full_key</code>, <code>algorithm</code>, and <code>fingerprint</code>. fetch_host_key = function( host, port, key_type ) local socket = nmap.new_socket() local status -- oakley group 2 prime taken from rfc 2409 local prime = "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF" 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} ) ) 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.print_debug( 2, "Hostkey type '%s' not supported by server.", key_type ) return end local e, g, x, p -- e = g^x mod p g = openssl.bignum_dec2bn( "2" ) p = openssl.bignum_hex2bn( prime ) x = openssl.bignum_pseudo_rand( 1024 ) e = openssl.bignum_mod_exp( g, x, p ) packet = transport.build( transport.kexdh_init( e ) ) status = socket:send( packet ) if not status then socket:close(); return end local kexdh_reply status, kexdh_reply = transport.receive_packet( socket ) kexdh_reply = transport.payload( kexdh_reply ) -- check for proper msg code if kexdh_reply:byte(1) ~= SSH2.SSH_MSG_KEXDH_REPLY then return end local _,public_host_key,bits,algorithm _, _, public_host_key = bin.unpack( ">ca", kexdh_reply ) if key_type == 'ssh-dss' then algorithm = "DSA" local p _, _, p = bin.unpack( ">aa", public_host_key ) bits = openssl.bignum_bin2bn( p ):num_bits() elseif key_type == 'ssh-rsa' then algorithm = "RSA" local n _, _, _, n = bin.unpack( ">aaa", 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" else stdnse.print_debug( "Unsupported key type: %s", key_type ) end return { key=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) } 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, } return _ENV;