merge: testing → main (reconcile 2-week divergence)

decnet/templates/llmnr/server.py

@@ -0,0 +1,113 @@
+#!/usr/bin/env python3
+"""
+LLMNR / mDNS poisoning detector (UDP 5355 and UDP 5353).
+Listens for any incoming name-resolution queries. Any traffic here is a
+strong signal of an attacker running Responder or similar tools on the LAN.
+Logs every packet with source IP and decoded query name where possible.
+"""
+
+import asyncio
+import os
+import struct
+from syslog_bridge import syslog_line, write_syslog_file, forward_syslog
+
+NODE_NAME = os.environ.get("NODE_NAME", "lan-host")
+SERVICE_NAME   = "llmnr"
+LOG_TARGET = os.environ.get("LOG_TARGET", "")
+
+
+
+
+def _log(event_type: str, severity: int = 6, **kwargs) -> None:
+    line = syslog_line(SERVICE_NAME, NODE_NAME, event_type, severity, **kwargs)
+    write_syslog_file(line)
+    forward_syslog(line, LOG_TARGET)
+
+
+def _decode_dns_name(data: bytes, offset: int) -> str:
+    """Decode a DNS-encoded label sequence starting at offset."""
+    labels = []
+    visited = set()
+    pos = offset
+    while pos < len(data):
+        if pos in visited:
+            break
+        visited.add(pos)
+        length = data[pos]
+        if length == 0:
+            break
+        if length & 0xc0 == 0xc0:  # pointer
+            if pos + 1 >= len(data):
+                break
+            ptr = ((length & 0x3f) << 8) | data[pos + 1]
+            labels.append(_decode_dns_name(data, ptr))
+            break
+        pos += 1
+        labels.append(data[pos:pos + length].decode(errors="replace"))
+        pos += length
+    return ".".join(labels)
+
+
+def _parse_query(data: bytes, proto: str, src_addr) -> None:
+    """Parse DNS/LLMNR/mDNS query and log the queried name."""
+    try:
+        if len(data) < 12:
+            raise ValueError("too short")
+        flags = struct.unpack(">H", data[2:4])[0]
+        qr = (flags >> 15) & 1
+        qdcount = struct.unpack(">H", data[4:6])[0]
+        if qr != 0 or qdcount < 1:
+            return  # not a query or no questions
+        name = _decode_dns_name(data, 12)
+        pos = 12
+        while pos < len(data) and data[pos] != 0:
+            pos += data[pos] + 1
+        pos += 1
+        qtype = struct.unpack(">H", data[pos:pos + 2])[0] if pos + 2 <= len(data) else 0
+        _log(
+            "query",
+            proto=proto,
+            src=src_addr[0],
+            src_port=src_addr[1],
+            name=name,
+            qtype=qtype,
+        )
+    except Exception as e:
+        _log("raw_packet", proto=proto, src=src_addr[0], data=data[:64].hex(), error=str(e))
+
+
+class LLMNRProtocol(asyncio.DatagramProtocol):
+    def __init__(self, proto_label: str):
+        self._proto = proto_label
+
+    def datagram_received(self, data, addr):
+        _parse_query(data, self._proto, addr)
+
+    def error_received(self, exc):
+        pass
+
+
+async def main():
+    _log("startup", msg=f"LLMNR/mDNS server starting as {NODE_NAME}")
+    loop = asyncio.get_running_loop()
+
+    # LLMNR: UDP 5355
+    llmnr_transport, _ = await loop.create_datagram_endpoint(
+        lambda: LLMNRProtocol("LLMNR"),
+        local_addr=("0.0.0.0", 5355),  # nosec B104
+    )
+    # mDNS: UDP 5353
+    mdns_transport, _ = await loop.create_datagram_endpoint(
+        lambda: LLMNRProtocol("mDNS"),
+        local_addr=("0.0.0.0", 5353),  # nosec B104
+    )
+
+    try:
+        await asyncio.sleep(float("inf"))
+    finally:
+        llmnr_transport.close()
+        mdns_transport.close()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())