Add support for websockets (#4578)

Author: lucasdrufva

scapy/contrib/websocket.py

@@ -0,0 +1,259 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+# This file is part of Scapy
+# See https://scapy.net/ for more information
+# Copyright (C) 2024 Lucas Drufva <[email protected]>
+
+# scapy.contrib.description = WebSocket
+# scapy.contrib.status = loads
+
+# Based on rfc6455
+
+import struct
+import base64
+import zlib
+from hashlib import sha1
+from scapy.fields import (BitFieldLenField, Field, BitField, BitEnumField, ConditionalField, XNBytesField)
+from scapy.layers.http import HTTPRequest, HTTPResponse
+from scapy.layers.inet import TCP
+from scapy.packet import Packet
+from scapy.error import Scapy_Exception
+import logging
+
+
+class PayloadLenField(BitFieldLenField):
+
+    def __init__(self, name, default, length_of, size=0, tot_size=0, end_tot_size=0):
+        # Initialize with length_of (like in BitFieldLenField) and lengthFrom (like in BitLenField)
+        super().__init__(name, default, size, length_of=length_of, tot_size=tot_size, end_tot_size=end_tot_size)
+
+    def getfield(self, pkt, s):
+        s, _ = s
+        # Get the 7-bit field (first byte)
+        length_byte = s[0] & 0x7F
+        s = s[1:]
+
+        if length_byte <= 125:
+            # 7-bit length
+            return s, length_byte
+        elif length_byte == 126:
+            # 16-bit length
+            length = struct.unpack("!H", s[:2])[0]  # Read 2 bytes
+            s = s[2:]
+            return s, length
+        elif length_byte == 127:
+            # 64-bit length
+            length = struct.unpack("!Q", s[:8])[0]  # Read 8 bytes
+            s = s[8:]
+            return s, length
+
+    def addfield(self, pkt, s, val):
+        p_field, p_val = pkt.getfield_and_val(self.length_of)
+        val = p_field.i2len(pkt, p_val)
+
+        if val <= 125:
+            self.size = 7
+            return super().addfield(pkt, s, val)
+        elif val <= 0xFFFF:
+            self.size = 7+16
+            s, _, masked = s
+            return s + struct.pack("!BH", 126 | masked, val)
+        elif val <= 0xFFFFFFFFFFFFFFFF:
+            self.size = 7+64
+            s, _, masked = s
+            return s + struct.pack("!BQ", 127 | masked, val)
+        else:
+            raise Scapy_Exception("%s: Payload length too large" %
+                                    self.__class__.__name__)
+
+
+
+class PayloadField(Field):
+    """
+    Field for handling raw byte payloads with dynamic size.
+    The length of the payload is described by a preceding PayloadLenField.
+    """
+    __slots__ = ["lengthFrom"]
+    
+    def __init__(self, name, lengthFrom):
+        """
+        :param name: Field name
+        :param lengthFrom: Field name that provides the length of the payload
+        """
+        super(PayloadField, self).__init__(name, None)
+        self.lengthFrom = lengthFrom
+
+    def getfield(self, pkt, s):
+        # Fetch the length from the field that specifies the length
+        length = getattr(pkt, self.lengthFrom)
+        payloadData = s[:length]
+
+        if pkt.mask:
+            key = struct.pack("I", pkt.maskingKey)[::-1]
+            data_int = int.from_bytes(payloadData, 'big')
+            mask_repeated = key * (len(payloadData) // 4) + key[: len(payloadData) % 4]
+            mask_int = int.from_bytes(mask_repeated, 'big')
+            payloadData = (data_int ^ mask_int).to_bytes(len(payloadData), 'big')
+
+        if("permessage-deflate" in pkt.extensions):
+            try:
+                payloadData = pkt.decoder[0](payloadData + b"\x00\x00\xff\xff")
+            except Exception: 
+                logging.debug("Failed to decompress payload", payloadData)
+
+        return s[length:], payloadData
+
+    def addfield(self, pkt, s, val):
+        if pkt.mask:
+            key = struct.pack("I", pkt.maskingKey)[::-1]
+            data_int = int.from_bytes(val, 'big')
+            mask_repeated = key * (len(val) // 4) + key[: len(val) % 4]
+            mask_int = int.from_bytes(mask_repeated, 'big')
+            val = (data_int ^ mask_int).to_bytes(len(val), 'big')
+
+        return s + bytes(val)
+
+    def i2len(self, pkt, val):
+        # Length of the payload in bytes
+        return len(val)
+
+class WebSocket(Packet):
+    __slots__ = ["extensions", "decoder"]
+
+    name = "WebSocket"
+    fields_desc = [
+        BitField("fin", 0, 1),
+        BitField("rsv", 0, 3),
+        BitEnumField("opcode", 0, 4, 
+            {
+                0x0: "none",
+                0x1: "text",
+                0x2: "binary",
+                0x8: "close",
+                0x9: "ping",
+                0xA: "pong",
+            }),
+        BitField("mask", 0, 1),
+        PayloadLenField("payloadLen", 0, length_of="wsPayload", size=1),
+        ConditionalField(XNBytesField("maskingKey", 0, sz=4), lambda pkt: pkt.mask == 1),
+        PayloadField("wsPayload", lengthFrom="payloadLen")
+    ]
+
+    def __init__(self, pkt=None, extensions=[], decoder=None, *args, **fields):
+        self.extensions = extensions
+        self.decoder = decoder
+        super().__init__(_pkt=pkt, *args, **fields)
+
+    def extract_padding(self, s):
+        return '', s
+
+    @classmethod
+    def tcp_reassemble(cls, data, metadata, session):
+        # data = the reassembled data from the same request/flow
+        # metadata = empty dictionary, that can be used to store data
+        #            during TCP reassembly
+        # session = a dictionary proper to the bidirectional TCP session,
+        #           that can be used to store anything
+        # [...]
+        # If the packet is available, return it. Otherwise don't.
+        # Whenever you return a packet, the buffer will be discarded.
+
+
+        HANDSHAKE_STATE_CLIENT_OPEN = 0
+        HANDSHAKE_STATE_SERVER_OPEN = 1
+        HANDSHAKE_STATE_OPEN = 2
+
+        if "handshake-state" not in session:
+            session["handshake-state"] = HANDSHAKE_STATE_CLIENT_OPEN
+
+        if "extensions" not in session:
+            session["extensions"] = {}
+
+
+        if session["handshake-state"] == HANDSHAKE_STATE_CLIENT_OPEN:
+            ht = HTTPRequest(data)
+
+            if ht.Method != b"GET":
+                return None
+
+            if not ht.Upgrade or ht.Upgrade.lower() != b"websocket":
+                return None
+            
+            if b"Sec-WebSocket-Key" not in ht.Unknown_Headers:
+                return None
+
+            
+            session["handshake-key"] = ht.Unknown_Headers[b"Sec-WebSocket-Key"]
+
+            if "original" in metadata:
+                session["server-port"] = metadata["original"][TCP].dport
+            else: 
+                print("No original packet")
+
+            session["handshake-state"] = HANDSHAKE_STATE_SERVER_OPEN
+            
+            return ht
+
+        elif session["handshake-state"] == HANDSHAKE_STATE_SERVER_OPEN:
+            ht = HTTPResponse(data)
+
+            if not ht.Upgrade.lower() == b"websocket":
+                return None
+            
+            # Verify key-accept handshake:
+            correct_accept = base64.b64encode(sha1(session["handshake-key"] + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11".encode()).digest())
+            if ht.Unknown_Headers[b"Sec-WebSocket-Accept"] != correct_accept:
+                #TODO handle or Logg wrong accept key
+                pass
+
+            if b"Sec-WebSocket-Extensions" in ht.Unknown_Headers:
+                session["extensions"] = {}
+                for extension in ht.Unknown_Headers[b"Sec-WebSocket-Extensions"].decode().strip().split(";"):
+                    key_value_pair = extension.split("=", 1) + [None]
+                    session["extensions"][key_value_pair[0].strip()] = key_value_pair[1]          
+
+                if "permessage-deflate" in session["extensions"]:
+                    def create_decompressor(window_bits):
+                        decoder = zlib.decompressobj(wbits=-window_bits)
+                        def decomp(data):
+                            nonlocal decoder
+                            return decoder.decompress(data, 0)
+                        
+                        def reset():
+                            nonlocal decoder
+                            nonlocal window_bits
+                            decoder = zlib.decompressobj(wbits=-window_bits)
+                        
+                        return (decomp, reset)
+                    
+                    # Default values
+                    client_wb = 12
+                    server_wb = 15
+
+                    # Check for new values in extensions header
+                    if "client_max_window_bits" in session["extensions"]:
+                        client_wb = int(session["extensions"]["client_max_window_bits"])
+                    
+                    if "server_max_window_bits" in session["extensions"]:
+                        server_wb = int(session["extensions"]["server_max_window_bits"])
+                        
+
+                    session["server-decoder"] = create_decompressor(client_wb)
+                    session["client-decoder"] = create_decompressor(server_wb)
+
+
+            session["handshake-state"] = HANDSHAKE_STATE_OPEN
+
+            return ht
+        
+
+        # Handshake is done:
+        if "original" not in metadata:
+            return
+        
+        if "permessage-deflate" in session["extensions"]:
+            is_server = True if metadata["original"][TCP].sport == session["server-port"] else False
+            ws = WebSocket(bytes(data), extensions=session["extensions"], decoder = session["server-decoder"] if is_server else session["client-decoder"])
+            return ws
+        else:
+            ws = WebSocket(bytes(data), extensions=session["extensions"])
+            return ws

scapy/layers/http.py

@@ -529,10 +529,10 @@ def do_dissect(self, s):
         """From the HTTP packet string, populate the scapy object"""
         first_line, body = _dissect_headers(self, s)
         try:
-            Method, Path, HTTPVersion = re.split(br"\s+", first_line, maxsplit=2)
-            self.setfieldval('Method', Method)
-            self.setfieldval('Path', Path)
-            self.setfieldval('Http_Version', HTTPVersion)
+            method_path_version = re.split(br"\s+", first_line, maxsplit=2) + [None]
+            self.setfieldval('Method', method_path_version[0])
+            self.setfieldval('Path', method_path_version[1])
+            self.setfieldval('Http_Version', method_path_version[2])
         except ValueError:
             pass
         if body:
@@ -573,10 +573,10 @@ def do_dissect(self, s):
         ''' From the HTTP packet string, populate the scapy object '''
         first_line, body = _dissect_headers(self, s)
         try:
-            HTTPVersion, Status, Reason = re.split(br"\s+", first_line, maxsplit=2)
-            self.setfieldval('Http_Version', HTTPVersion)
-            self.setfieldval('Status_Code', Status)
-            self.setfieldval('Reason_Phrase', Reason)
+            version_status_reason = re.split(br"\s+", first_line, maxsplit=2) + [None]
+            self.setfieldval('Http_Version', version_status_reason[0])
+            self.setfieldval('Status_Code', version_status_reason[1])
+            self.setfieldval('Reason_Phrase', version_status_reason[2])
         except ValueError:
             pass
         if body:

test/contrib/websocket.uts

@@ -0,0 +1,82 @@
+# WebSocket layer unit tests
+# Copyright (C) 2024 Lucas Drufva <[email protected]>
+#
+# Type the following command to launch start the tests:
+# $ test/run_tests -P "load_contrib('websocket')" -t test/contrib/websocket.uts
+
++ Syntax check
+= Import the WebSocket layer
+from scapy.contrib.websocket import *
+
++ WebSocket protocol test
+= Packet instantiation
+pkt = WebSocket(wsPayload=b"Hello, world!", opcode="text", mask=True, maskingKey=0x11223344)
+
+assert pkt.wsPayload == b"Hello, world!"
+assert pkt.mask == True
+assert pkt.maskingKey == 0x11223344
+
+
+= Packet dissection
+raw = b'\x01\x0dHello, world!'
+pkt = WebSocket(raw)
+
+assert pkt.fin == 0
+assert pkt.rsv == 0
+assert pkt.opcode == 0x1
+assert pkt.mask == False
+assert pkt.payloadLen == 13
+assert pkt.wsPayload == b'Hello, world!'
+
+= Dissect masked packet
+raw = b'\x01\x8d\x11\x22\x33\x44\x59\x47\x5f\x28\x7e\x0e\x13\x33\x7e\x50\x5f\x20\x30'
+pkt = WebSocket(raw)
+
+assert pkt.fin == 0
+assert pkt.rsv == 0
+assert pkt.opcode == 0x1
+assert pkt.mask == True
+assert pkt.payloadLen == 13
+assert pkt.wsPayload == b'Hello, world!'
+
+= Session with compression
+
+bind_layers(TCP, WebSocket, dport=5000)
+bind_layers(TCP, WebSocket, sport=5000)
+
+from scapy.sessions import TCPSession
+
+filename = scapy_path("/test/pcaps/websocket_compressed_session.pcap")
+pkts = sniff(offline=filename, session=TCPSession)
+
+assert len(pkts) == 13
+
+assert pkts[7][WebSocket].wsPayload == b'Hello'
+assert pkts[8][WebSocket].wsPayload == b'"Hello"'
+assert pkts[10][WebSocket].wsPayload == b'Hello2'
+assert pkts[11][WebSocket].wsPayload == b'"Hello2"'
+
+= Create packet with long payload
+pkt = WebSocket(wsPayload=b"a"*126, opcode="text")
+
+assert bytes(pkt) == b'\x01\x7e\x00\x7e\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61'
+
+= Dissect packet with long payload
+raw = b'\x01\x7e\x00\x7e\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61\x61'
+pkt = WebSocket(raw)
+
+assert pkt.payloadLen == 126
+assert pkt.wsPayload == b'a'*126
+
+= Create packet with very long payload
+pkt = WebSocket(wsPayload=b"a"*65536, opcode="text")
+
+assert bytes(pkt) == b'\x01\x7f\x00\x00\x00\x00\x00\x01\x00\x00' + b'a'*65536
+
+= Dissect packet with very long payload
+raw = b'\x01\x7f\x00\x00\x00\x00\x00\x01\x00\x00' + b'a'*65536
+pkt = WebSocket(raw)
+
+assert pkt.payloadLen == 65536
+assert pkt.wsPayload == b'a'*65536
+