anti
988732f4f9
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115 lines
3.3 KiB
Python
115 lines
3.3 KiB
Python
#!/usr/bin/env python3
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"""
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LLMNR / mDNS poisoning detector (UDP 5355 and UDP 5353).
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Listens for any incoming name-resolution queries. Any traffic here is a
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strong signal of an attacker running Responder or similar tools on the LAN.
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Logs every packet with source IP and decoded query name where possible.
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"""
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import asyncio
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import os
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import struct
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from decnet_logging import syslog_line, write_syslog_file, forward_syslog
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NODE_NAME = os.environ.get("NODE_NAME", "lan-host")
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SERVICE_NAME = "llmnr"
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LOG_TARGET = os.environ.get("LOG_TARGET", "")
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def _log(event_type: str, severity: int = 6, **kwargs) -> None:
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line = syslog_line(SERVICE_NAME, NODE_NAME, event_type, severity, **kwargs)
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print(line, flush=True)
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write_syslog_file(line)
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forward_syslog(line, LOG_TARGET)
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def _decode_dns_name(data: bytes, offset: int) -> str:
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"""Decode a DNS-encoded label sequence starting at offset."""
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labels = []
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visited = set()
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pos = offset
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while pos < len(data):
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if pos in visited:
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break
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visited.add(pos)
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length = data[pos]
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if length == 0:
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break
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if length & 0xc0 == 0xc0: # pointer
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if pos + 1 >= len(data):
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break
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ptr = ((length & 0x3f) << 8) | data[pos + 1]
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labels.append(_decode_dns_name(data, ptr))
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break
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pos += 1
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labels.append(data[pos:pos + length].decode(errors="replace"))
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pos += length
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return ".".join(labels)
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def _parse_query(data: bytes, proto: str, src_addr) -> None:
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"""Parse DNS/LLMNR/mDNS query and log the queried name."""
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try:
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if len(data) < 12:
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raise ValueError("too short")
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flags = struct.unpack(">H", data[2:4])[0]
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qr = (flags >> 15) & 1
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qdcount = struct.unpack(">H", data[4:6])[0]
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if qr != 0 or qdcount < 1:
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return # not a query or no questions
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name = _decode_dns_name(data, 12)
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pos = 12
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while pos < len(data) and data[pos] != 0:
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pos += data[pos] + 1
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pos += 1
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qtype = struct.unpack(">H", data[pos:pos + 2])[0] if pos + 2 <= len(data) else 0
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_log(
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"query",
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proto=proto,
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src=src_addr[0],
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src_port=src_addr[1],
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name=name,
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qtype=qtype,
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)
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except Exception as e:
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_log("raw_packet", proto=proto, src=src_addr[0], data=data[:64].hex(), error=str(e))
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class LLMNRProtocol(asyncio.DatagramProtocol):
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def __init__(self, proto_label: str):
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self._proto = proto_label
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def datagram_received(self, data, addr):
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_parse_query(data, self._proto, addr)
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def error_received(self, exc):
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pass
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async def main():
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_log("startup", msg=f"LLMNR/mDNS server starting as {NODE_NAME}")
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loop = asyncio.get_running_loop()
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# LLMNR: UDP 5355
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llmnr_transport, _ = await loop.create_datagram_endpoint(
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lambda: LLMNRProtocol("LLMNR"),
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local_addr=("0.0.0.0", 5355),
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)
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# mDNS: UDP 5353
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mdns_transport, _ = await loop.create_datagram_endpoint(
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lambda: LLMNRProtocol("mDNS"),
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local_addr=("0.0.0.0", 5353),
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)
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try:
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await asyncio.sleep(float("inf"))
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finally:
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llmnr_transport.close()
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mdns_transport.close()
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if __name__ == "__main__":
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asyncio.run(main())
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