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From: Jakub Witczak <kuba@erlang.org>
Date: Mon, 14 Apr 2025 16:33:21 +0200
Subject: ssh: early RCE fix
The patch fixes remote code execution (RCE) by an unauthenticated user.
- disconnect when connection protocol message arrives
- when user is not authenticated for connection
- see RFC4252 sec.6
Origin: https://github.com/erlang/otp/commit/0fcd9c56524b28615e8ece65fc0c3f66ef6e4c12
Bug-Debian: https://bugs.debian.org/1103442
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2025-32433
--- a/lib/ssh/src/ssh_connection.erl
+++ b/lib/ssh/src/ssh_connection.erl
@@ -26,6 +26,8 @@
-module(ssh_connection).
+-include_lib("kernel/include/logger.hrl").
+
-include("ssh.hrl").
-include("ssh_connect.hrl").
-include("ssh_transport.hrl").
@@ -468,6 +470,25 @@
%%% Replies {Reply, UpdatedConnection}
%%%
+handle_msg(#ssh_msg_disconnect{code = Code, description = Description}, Connection, _, _SSH) ->
+ {disconnect, {Code, Description}, handle_stop(Connection)};
+
+handle_msg(Msg, Connection, server, Ssh = #ssh{authenticated = false}) ->
+ %% See RFC4252 6.
+ %% Message numbers of 80 and higher are reserved for protocols running
+ %% after this authentication protocol, so receiving one of them before
+ %% authentication is complete is an error, to which the server MUST
+ %% respond by disconnecting, preferably with a proper disconnect message
+ %% sent to ease troubleshooting.
+ MsgFun = fun(M) ->
+ MaxLogItemLen = ?GET_OPT(max_log_item_len, Ssh#ssh.opts),
+ io_lib:format("Connection terminated. Unexpected message for unauthenticated user."
+ " Message: ~w", [M],
+ [{chars_limit, MaxLogItemLen}])
+ end,
+ ?LOG_DEBUG(MsgFun, [Msg]),
+ {disconnect, {?SSH_DISCONNECT_PROTOCOL_ERROR, "Connection refused"}, handle_stop(Connection)};
+
handle_msg(#ssh_msg_channel_open_confirmation{recipient_channel = ChannelId,
sender_channel = RemoteId,
initial_window_size = WindowSz,
@@ -966,12 +987,7 @@
#connection{requests = [{_, From, Fun} | Rest]} = Connection0, _, _SSH) ->
Connection = Fun({success,Data}, Connection0),
{[{channel_request_reply, From, {success, Data}}],
- Connection#connection{requests = Rest}};
-
-handle_msg(#ssh_msg_disconnect{code = Code,
- description = Description},
- Connection, _, _SSH) ->
- {disconnect, {Code, Description}, handle_stop(Connection)}.
+ Connection#connection{requests = Rest}}.
%%%----------------------------------------------------------------
--- a/lib/ssh/test/ssh_protocol_SUITE.erl
+++ b/lib/ssh/test/ssh_protocol_SUITE.erl
@@ -73,6 +73,7 @@
no_common_alg_client_disconnects/1,
no_common_alg_server_disconnects/1,
custom_kexinit/1,
+ early_rce/1,
no_ext_info_s1/1,
no_ext_info_s2/1,
packet_length_too_large/1,
@@ -111,6 +112,7 @@
all() ->
[{group,tool_tests},
client_info_line,
+ early_rce,
{group,kex},
{group,service_requests},
{group,authentication},
@@ -129,10 +131,8 @@
]},
{packet_size_error, [], [packet_length_too_large,
packet_length_too_short]},
-
{field_size_error, [], [service_name_length_too_large,
service_name_length_too_short]},
-
{kex, [], [custom_kexinit,
no_common_alg_server_disconnects,
no_common_alg_client_disconnects,
@@ -175,7 +175,8 @@
end_per_suite(Config) ->
stop_apps(Config).
-init_per_testcase(Tc, Config) when Tc == no_common_alg_server_disconnects; Tc == custom_kexinit ->
+init_per_testcase(Tc, Config) when Tc == no_common_alg_server_disconnects;
+ Tc == custom_kexinit ->
start_std_daemon(Config, [{preferred_algorithms,[{public_key,['ssh-rsa']},
{cipher,?DEFAULT_CIPHERS}
]}]);
@@ -221,7 +222,8 @@
init_per_testcase(_TestCase, Config) ->
check_std_daemon_works(Config, ?LINE).
-end_per_testcase(Tc, Config) when Tc == no_common_alg_server_disconnects; Tc == custom_kexinit ->
+end_per_testcase(Tc, Config) when Tc == no_common_alg_server_disconnects;
+ Tc == custom_kexinit ->
stop_std_daemon(Config);
end_per_testcase(kex_strict_negotiated, Config) ->
Config;
@@ -382,6 +384,44 @@
]
).
+early_rce(Config) ->
+ {ok,InitialState} =
+ ssh_trpt_test_lib:exec([{set_options, [print_ops, print_seqnums, print_messages]}]),
+ TypeOpen = "session",
+ ChannelId = 0,
+ WinSz = 425984,
+ PktSz = 65536,
+ DataOpen = <<>>,
+ SshMsgChannelOpen = ssh_connection:channel_open_msg(TypeOpen, ChannelId, WinSz, PktSz, DataOpen),
+
+ Id = 0,
+ TypeReq = "exec",
+ WantReply = true,
+ DataReq = <<?STRING(<<"lists:seq(1,10).">>)>>,
+ SshMsgChannelRequest =
+ ssh_connection:channel_request_msg(Id, TypeReq, WantReply, DataReq),
+ {ok,AfterKexState} =
+ ssh_trpt_test_lib:exec(
+ [{connect,
+ server_host(Config),server_port(Config),
+ [{preferred_algorithms,[{kex,[?DEFAULT_KEX]},
+ {cipher,?DEFAULT_CIPHERS}
+ ]},
+ {silently_accept_hosts, true},
+ {recv_ext_info, false},
+ {user_dir, user_dir(Config)},
+ {user_interaction, false}
+ | proplists:get_value(extra_options,Config,[])]},
+ receive_hello,
+ {send, hello},
+ {send, ssh_msg_kexinit},
+ {match, #ssh_msg_kexinit{_='_'}, receive_msg},
+ {send, SshMsgChannelOpen},
+ {send, SshMsgChannelRequest},
+ {match, disconnect(), receive_msg}
+ ], InitialState),
+ ok.
+
custom_kexinit(Config) ->
%% 16#C0 value causes unicode:characters_to_list to return a big error value
Trash = lists:duplicate(260_000, 16#C0),
@@ -408,11 +448,6 @@
first_kex_packet_follows = false,
reserved = 0
},
- PacketFun =
- fun(Msg, Ssh) ->
- BinMsg = custom_encode(Msg),
- ssh_transport:pack(BinMsg, Ssh, 0)
- end,
{ok,_} =
ssh_trpt_test_lib:exec(
[{set_options, [print_ops, {print_messages,detail}]},
@@ -428,42 +463,11 @@
receive_hello,
{send, hello},
{match, #ssh_msg_kexinit{_='_'}, receive_msg},
- {send, {special, KexInit, PacketFun}}, % with server unsupported 'ssh-dss' !
+ {send, KexInit}, % with server unsupported 'ssh-dss' !
{match, disconnect(), receive_msg}
]
).
-custom_encode(#ssh_msg_kexinit{
- cookie = Cookie,
- kex_algorithms = KeyAlgs,
- server_host_key_algorithms = HostKeyAlgs,
- encryption_algorithms_client_to_server = EncAlgC2S,
- encryption_algorithms_server_to_client = EncAlgS2C,
- mac_algorithms_client_to_server = MacAlgC2S,
- mac_algorithms_server_to_client = MacAlgS2C,
- compression_algorithms_client_to_server = CompAlgS2C,
- compression_algorithms_server_to_client = CompAlgC2S,
- languages_client_to_server = LangC2S,
- languages_server_to_client = LangS2C,
- first_kex_packet_follows = Bool,
- reserved = Reserved
- }) ->
- KeyAlgsBin0 = <<?Ename_list(KeyAlgs)>>,
- <<?UINT32(Len0), Data:Len0/binary>> = KeyAlgsBin0,
- KeyAlgsBin = <<?UINT32(Len0), Data/binary>>,
- <<?Ebyte(?SSH_MSG_KEXINIT), Cookie/binary,
- KeyAlgsBin/binary,
- ?Ename_list(HostKeyAlgs),
- ?Ename_list(EncAlgC2S),
- ?Ename_list(EncAlgS2C),
- ?Ename_list(MacAlgC2S),
- ?Ename_list(MacAlgS2C),
- ?Ename_list(CompAlgS2C),
- ?Ename_list(CompAlgC2S),
- ?Ename_list(LangC2S),
- ?Ename_list(LangS2C),
- ?Eboolean(Bool), ?Euint32(Reserved)>>.
-
%%--------------------------------------------------------------------
%%% Algo negotiation fail. This should result in a ssh_msg_disconnect
%%% being sent from the client.
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