websocket: Limit maximum uncompressed frame length to 8MiB

This fixes a memory exhaustion DOS attack vector.

References: GHSA-9p9m-jm8w-94p2
GHSA-9p9m-jm8w-94p2

eventlet/websocket.py

@@ -38,6 +38,7 @@
         break
 
 ACCEPTABLE_CLIENT_ERRORS = set((errno.ECONNRESET, errno.EPIPE))
+DEFAULT_MAX_FRAME_LENGTH = 8 << 20
 
 __all__ = ["WebSocketWSGI", "WebSocket"]
 PROTOCOL_GUID = b'258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
@@ -75,14 +76,20 @@ def my_handler(ws):
     :class:`WebSocket`.  To close the socket, simply return from the
     function.  Note that the server will log the websocket request at
     the time of closure.
+
+    An optional argument max_frame_length can be given, which will set the
+    maximum incoming *uncompressed* payload length of a frame. By default, this
+    is set to 8MiB. Note that excessive values here might create a DOS attack
+    vector.
     """
 
-    def __init__(self, handler):
+    def __init__(self, handler, max_frame_length=DEFAULT_MAX_FRAME_LENGTH):
         self.handler = handler
         self.protocol_version = None
         self.support_legacy_versions = True
         self.supported_protocols = []
         self.origin_checker = None
+        self.max_frame_length = max_frame_length
 
     @classmethod
     def configured(cls,
@@ -324,7 +331,8 @@ def _handle_hybi_request(self, environ):
         sock.sendall(b'\r\n'.join(handshake_reply) + b'\r\n\r\n')
         return RFC6455WebSocket(sock, environ, self.protocol_version,
                                 protocol=negotiated_protocol,
-                                extensions=parsed_extensions)
+                                extensions=parsed_extensions,
+                                max_frame_length=self.max_frame_length)
 
     def _extract_number(self, value):
         """
@@ -503,7 +511,8 @@ class ProtocolError(ValueError):
 
 
 class RFC6455WebSocket(WebSocket):
-    def __init__(self, sock, environ, version=13, protocol=None, client=False, extensions=None):
+    def __init__(self, sock, environ, version=13, protocol=None, client=False, extensions=None,
+                 max_frame_length=DEFAULT_MAX_FRAME_LENGTH):
         super(RFC6455WebSocket, self).__init__(sock, environ, version)
         self.iterator = self._iter_frames()
         self.client = client
@@ -512,6 +521,8 @@ def __init__(self, sock, environ, version=13, protocol=None, client=False, exten
 
         self._deflate_enc = None
         self._deflate_dec = None
+        self.max_frame_length = max_frame_length
+        self._remote_close_data = None
 
     class UTF8Decoder(object):
         def __init__(self):
@@ -583,12 +594,13 @@ def _get_bytes(self, numbytes):
         return data
 
     class Message(object):
-        def __init__(self, opcode, decoder=None, decompressor=None):
+        def __init__(self, opcode, max_frame_length, decoder=None, decompressor=None):
             self.decoder = decoder
             self.data = []
             self.finished = False
             self.opcode = opcode
             self.decompressor = decompressor
+            self.max_frame_length = max_frame_length
 
         def push(self, data, final=False):
             self.finished = final
@@ -597,7 +609,12 @@ def push(self, data, final=False):
         def getvalue(self):
             data = b"".join(self.data)
             if not self.opcode & 8 and self.decompressor:
-                data = self.decompressor.decompress(data + b'\x00\x00\xff\xff')
+                data = self.decompressor.decompress(data + b"\x00\x00\xff\xff", self.max_frame_length)
+                if self.decompressor.unconsumed_tail:
+                    raise FailedConnectionError(
+                        1009,
+                        "Incoming compressed frame exceeds length limit of {} bytes.".format(self.max_frame_length))
+
             if self.decoder:
                 data = self.decoder.decode(data, self.finished)
             return data
@@ -611,6 +628,7 @@ def _apply_mask(data, mask, length=None, offset=0):
 
     def _handle_control_frame(self, opcode, data):
         if opcode == 8:  # connection close
+            self._remote_close_data = data
             if not data:
                 status = 1000
             elif len(data) > 1:
@@ -710,13 +728,17 @@ def _recv_frame(self, message=None):
             length = struct.unpack('!H', recv(2))[0]
         elif length == 127:
             length = struct.unpack('!Q', recv(8))[0]
+
+        if length > self.max_frame_length:
+            raise FailedConnectionError(1009, "Incoming frame of {} bytes is above length limit of {} bytes.".format(
+                length, self.max_frame_length))
         if masked:
             mask = struct.unpack('!BBBB', recv(4))
         received = 0
         if not message or opcode & 8:
             decoder = self.UTF8Decoder() if opcode == 1 else None
             decompressor = self._get_permessage_deflate_dec(rsv1)
-            message = self.Message(opcode, decoder=decoder, decompressor=decompressor)
+            message = self.Message(opcode, self.max_frame_length, decoder=decoder, decompressor=decompressor)
         if not length:
             message.push(b'', final=finished)
         else:

tests/websocket_new_test.py

@@ -30,7 +30,12 @@ def handle(ws):
     else:
         ws.close()
 
-wsapp = websocket.WebSocketWSGI(handle)
+
+# Set a lower limit of DEFAULT_MAX_FRAME_LENGTH for testing, as
+# sending an 8MiB frame over the loopback interface can trigger a
+# timeout.
+TEST_MAX_FRAME_LENGTH = 50000
+wsapp = websocket.WebSocketWSGI(handle, max_frame_length=TEST_MAX_FRAME_LENGTH)
 
 
 class TestWebSocket(tests.wsgi_test._TestBase):
@@ -534,3 +539,55 @@ def test_compressed_send_recv_both_no_context_13(self):
 
         ws.close()
         eventlet.sleep(0.01)
+
+    def test_large_frame_size_compressed_13(self):
+        # Test fix for GHSA-9p9m-jm8w-94p2
+        extensions_string = 'permessage-deflate'
+        extensions = {'permessage-deflate': {
+            'client_no_context_takeover': False,
+            'server_no_context_takeover': False}}
+
+        sock = eventlet.connect(self.server_addr)
+        sock.sendall(six.b(self.connect % extensions_string))
+        sock.recv(1024)
+        ws = websocket.RFC6455WebSocket(sock, {}, client=True, extensions=extensions)
+
+        should_still_fit = b"x" * TEST_MAX_FRAME_LENGTH
+        one_too_much = should_still_fit + b"x"
+
+        # send just fitting frame twice to make sure they are fine independently
+        ws.send(should_still_fit)
+        assert ws.wait() == should_still_fit
+        ws.send(should_still_fit)
+        assert ws.wait() == should_still_fit
+        ws.send(one_too_much)
+
+        res = ws.wait()
+        assert res is None # socket closed
+        # TODO: The websocket currently sents compressed control frames, which contradicts RFC7692.
+        # Renable the following assert after that has been fixed.
+        # assert ws._remote_close_data == b"\x03\xf1Incoming compressed frame is above length limit."
+        eventlet.sleep(0.01)
+
+    def test_large_frame_size_uncompressed_13(self):
+        # Test fix for GHSA-9p9m-jm8w-94p2
+        sock = eventlet.connect(self.server_addr)
+        sock.sendall(six.b(self.connect))
+        sock.recv(1024)
+        ws = websocket.RFC6455WebSocket(sock, {}, client=True)
+
+        should_still_fit = b"x" * TEST_MAX_FRAME_LENGTH
+        one_too_much = should_still_fit + b"x"
+
+        # send just fitting frame twice to make sure they are fine independently
+        ws.send(should_still_fit)
+        assert ws.wait() == should_still_fit
+        ws.send(should_still_fit)
+        assert ws.wait() == should_still_fit
+        ws.send(one_too_much)
+
+        res = ws.wait()
+        assert res is None # socket closed
+        # close code should be available now
+        assert ws._remote_close_data == b"\x03\xf1Incoming frame of 50001 bytes is above length limit of 50000 bytes."
+        eventlet.sleep(0.01)