1 files changed, 403 insertions, 0 deletions
diff --git a/nselib/ssh2.lua b/nselib/ssh2.lua
new file mode 100644
index 0000000..e8707c8
--- /dev/null
+++ b/nselib/ssh2.lua
@@ -0,0 +1,403 @@
+---
+-- Functions for the SSH-2 protocol.
+--
+-- @author Sven Klemm <sven@c3d2.de>
+-- @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 <code>openssl</code> 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 <code>kexdh_init</code> packet.
+transport.kexdh_init = function( e )
+  return string.pack( "B", SSH2.SSH_MSG_KEXDH_INIT) .. transport.pack_mpint( e )
+end
+
+--- Build a <code>kexdh_gex_init</code> 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 <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 = 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 <code>kexinit</code> 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: <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 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;