feat: DCC stripping in both directions to prevent IP leaks

Block all non-ACTION CTCP/DCC from client-to-server (outbound) and add
security logging when inbound CTCP/DCC is stripped. Hard boundary with
no config toggle -- DCC exposes the client's real IP which defeats the
stealth proxy architecture.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/CHEATSHEET.md

@@ -187,6 +187,12 @@ notify_proxy = false                       # use SOCKS5 for notifications
 
 Only fires when no clients are attached.
 
+## Security
+
+- DCC/CTCP stripped both directions (prevents IP leaks). ACTION preserved.
+- All server connections routed through SOCKS5 proxy.
+- Stealth connect: random nick/user/realname on every connection.
+
 ## Hot Reload
 
 ```bash

docs/USAGE.md

@@ -651,6 +651,18 @@ Removing a channel also clears its key:
 /msg *bouncer AUTOJOIN libera -#secret
 ```
 
+## DCC Stripping
+
+DCC requests (`DCC SEND`, `DCC CHAT`) embed the sender's real IP address in the
+protocol payload. The bouncer strips all DCC and non-ACTION CTCP messages in
+both directions:
+
+- **Inbound** (server to client): silently dropped, logged as warning
+- **Outbound** (client to server): blocked before reaching the network
+
+ACTION (`/me`) is preserved. This is a hard security boundary -- there is no
+config toggle to disable it.
+
 ## Hot Reload
 
 The bouncer reloads its config file on `SIGHUP` or via the `REHASH` command.

src/bouncer/router.py

@@ -67,12 +67,14 @@ def _suppress(msg: IRCMessage) -> bool:
     # CTCP replies in NOTICE
     if msg.command == "NOTICE" and len(msg.params) >= 2:
         if msg.params[1].startswith(_CTCP_MARKER):
+            log.warning("stripped inbound CTCP reply: %s %.80s", msg.prefix, msg.params[1])
             return True
 
     # CTCP/DCC inside PRIVMSG (keep ACTION)
     if msg.command == "PRIVMSG" and len(msg.params) >= 2:
         text = msg.params[1]
         if text.startswith(_CTCP_MARKER) and not text.startswith("\x01ACTION"):
+            log.warning("stripped inbound CTCP/DCC: %s %.80s", msg.prefix, text)
             return True
 
     # User mode changes (MODE for non-channel targets)
@@ -162,6 +164,13 @@ class Router:
         if not msg.params:
             return
 
+        # Block outbound CTCP/DCC (except ACTION) -- prevents IP leaks
+        if msg.command in ("PRIVMSG", "NOTICE") and len(msg.params) >= 2:
+            text = msg.params[1]
+            if text.startswith(_CTCP_MARKER) and not text.startswith("\x01ACTION"):
+                log.warning("blocked outbound CTCP/DCC: %.80s", text)
+                return
+
         if msg.command == "KICK" and len(msg.params) >= 2:
             # KICK #channel/net nick/net :reason
             raw_chan, net = decode_target(msg.params[0])

tests/test_router.py

@@ -154,6 +154,16 @@ class TestSuppress:
         msg = _msg("TOPIC", ["#test", "new topic"], prefix="user!i@h")
         assert _suppress(msg) is False
 
+    def test_suppresses_dcc_send(self) -> None:
+        msg = _msg("PRIVMSG", ["nick", "\x01DCC SEND file 3232235777 5000 1024\x01"],
+                    prefix="user!i@h")
+        assert _suppress(msg) is True
+
+    def test_suppresses_dcc_chat(self) -> None:
+        msg = _msg("PRIVMSG", ["nick", "\x01DCC CHAT chat 3232235777 5000\x01"],
+                    prefix="user!i@h")
+        assert _suppress(msg) is True
+
 
 # -- Router._proxy_for ------------------------------------------------------
 
@@ -545,6 +555,46 @@ class TestRouteClientMessage:
         sent = net.send.call_args[0][0]
         assert sent.prefix == "me!u@h"
 
+    @pytest.mark.asyncio
+    async def test_blocks_outbound_dcc_send(self) -> None:
+        router = Router(_config(), _backlog())
+        net = _mock_network("libera")
+        router.networks["libera"] = net
+
+        msg = _msg("PRIVMSG", ["user/libera", "\x01DCC SEND file 3232235777 5000 1024\x01"])
+        await router.route_client_message(msg)
+        net.send.assert_not_awaited()
+
+    @pytest.mark.asyncio
+    async def test_blocks_outbound_dcc_chat(self) -> None:
+        router = Router(_config(), _backlog())
+        net = _mock_network("libera")
+        router.networks["libera"] = net
+
+        msg = _msg("PRIVMSG", ["user/libera", "\x01DCC CHAT chat 3232235777 5000\x01"])
+        await router.route_client_message(msg)
+        net.send.assert_not_awaited()
+
+    @pytest.mark.asyncio
+    async def test_passes_outbound_action(self) -> None:
+        router = Router(_config(), _backlog())
+        net = _mock_network("libera")
+        router.networks["libera"] = net
+
+        msg = _msg("PRIVMSG", ["#test/libera", "\x01ACTION waves\x01"])
+        await router.route_client_message(msg)
+        net.send.assert_awaited_once()
+
+    @pytest.mark.asyncio
+    async def test_passes_outbound_normal_privmsg(self) -> None:
+        router = Router(_config(), _backlog())
+        net = _mock_network("libera")
+        router.networks["libera"] = net
+
+        msg = _msg("PRIVMSG", ["#test/libera", "just a normal message"])
+        await router.route_client_message(msg)
+        net.send.assert_awaited_once()
+
 
 # -- _dispatch (inbound: network -> clients) ---------------------------------