SCRAM optional parameter parsing bugfix

The server gave an authentication error, if optional parameters
were present in the GS2 Header. Specifically, the "a=" parameter,
that can be used by admins to login as a different user.

diff --git a/src/cyrsasl_scram.erl b/src/cyrsasl_scram.erl
index 33d18cd1a4075aba28fb49aca145d9da9606461d..ee68bed1efce0fbdf7773e7b7cb5154bbbb1497c 100644 (file)
--- a/src/cyrsasl_scram.erl
+++ b/src/cyrsasl_scram.erl
@@ -32,6 +32,8 @@
 
 -include("ejabberd.hrl").
 
+-include("jlib.hrl").
+
 -behaviour(cyrsasl).
 
 -record(state,
@@ -60,8 +62,11 @@ mech_new(_Host, GetPassword, _CheckPassword,
     {ok, #state{step = 2, get_password = GetPassword}}.
 
 mech_step(#state{step = 2} = State, ClientIn) ->
-    case str:tokens(ClientIn, <<",">>) of
-      [CBind, UserNameAttribute, ClientNonceAttribute]
+    case re:split(ClientIn, <<",">>, [{return, binary}]) of
+      [_CBind, _AuthorizationIdentity, _UserNameAttribute, _ClientNonceAttribute, ExtensionAttribute | _]
+         when ExtensionAttribute /= [] ->
+         {error, <<"protocol-error-extension-not-supported">>};
+      [CBind, _AuthorizationIdentity, UserNameAttribute, ClientNonceAttribute | _]
          when (CBind == <<"y">>) or (CBind == <<"n">>) ->
          case parse_attribute(UserNameAttribute) of
            {error, Reason} -> {error, Reason};
@@ -123,42 +128,44 @@ mech_step(#state{step = 4} = State, ClientIn) ->
       [GS2ChannelBindingAttribute, NonceAttribute,
        ClientProofAttribute] ->
          case parse_attribute(GS2ChannelBindingAttribute) of
-           {$c, CVal} when (CVal == <<"biws">>) or (CVal == <<"eSws">>) ->
-               %% biws is base64 for n,, => channelbinding not supported
-               %% eSws is base64 for y,, => channelbinding supported by client only
-               Nonce = <<(State#state.client_nonce)/binary,
-                         (State#state.server_nonce)/binary>>,
-               case parse_attribute(NonceAttribute) of
-                 {$r, CompareNonce} when CompareNonce == Nonce ->
-                     case parse_attribute(ClientProofAttribute) of
-                       {$p, ClientProofB64} ->
-                           ClientProof = jlib:decode_base64(ClientProofB64),
-                           AuthMessage =
-                                  iolist_to_binary(
-                                    [State#state.auth_message,
-                                     ",",
-                                     str:substr(ClientIn, 1,
-                                                str:str(ClientIn, <<",p=">>)
-                                                - 1)]),
-                           ClientSignature =
-                               scram:client_signature(State#state.stored_key,
-                                                      AuthMessage),
-                           ClientKey = scram:client_key(ClientProof,
-                                                        ClientSignature),
-                           CompareStoredKey = scram:stored_key(ClientKey),
-                           if CompareStoredKey == State#state.stored_key ->
-                                  ServerSignature =
-                                      scram:server_signature(State#state.server_key,
-                                                             AuthMessage),
-                                  {ok, [{username, State#state.username}],
-                                   <<"v=",
-                                     (jlib:encode_base64(ServerSignature))/binary>>};
-                              true -> {error, <<"bad-auth">>}
+           {$c, CVal} ->
+               ChannelBindingSupport = binary:at(jlib:decode_base64(CVal), 0),
+               if (ChannelBindingSupport == $n)
+                 or (ChannelBindingSupport == $y) ->
+                   Nonce = <<(State#state.client_nonce)/binary,
+                               (State#state.server_nonce)/binary>>,
+                   case parse_attribute(NonceAttribute) of
+                       {$r, CompareNonce} when CompareNonce == Nonce ->
+                           case parse_attribute(ClientProofAttribute) of
+                           {$p, ClientProofB64} ->
+                                 ClientProof = jlib:decode_base64(ClientProofB64),
+                                 AuthMessage = iolist_to_binary(
+                                                   [State#state.auth_message,
+                                                    ",",
+                                                    str:substr(ClientIn, 1,
+                                                                   str:str(ClientIn, <<",p=">>)
+                                                                   - 1)]),
+                                 ClientSignature =
+                                   scram:client_signature(State#state.stored_key,
+                                                            AuthMessage),
+                                 ClientKey = scram:client_key(ClientProof,
+                                                            ClientSignature),
+                                 CompareStoredKey = scram:stored_key(ClientKey),
+                                 if CompareStoredKey == State#state.stored_key ->
+                                        ServerSignature =
+                                            scram:server_signature(State#state.server_key,
+                                                                   AuthMessage),
+                                        {ok, [{username, State#state.username}],
+                                         <<"v=",
+                                           (jlib:encode_base64(ServerSignature))/binary>>};
+                                    true -> {error, <<"bad-auth">>}
+                                 end;
+                           _Else -> {error, <<"bad-protocol">>}
                            end;
+                       {$r, _} -> {error, <<"bad-nonce">>};
                        _Else -> {error, <<"bad-protocol">>}
-                     end;
-                 {$r, _} -> {error, <<"bad-nonce">>};
-                 _Else -> {error, <<"bad-protocol">>}
+                   end;
+                 true -> {error, <<"bad-channel-binding">>}
                end;
            _Else -> {error, <<"bad-protocol">>}
          end;