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PYTHON-5906 Raise ProtocolError for malformed OP_COMPRESSED messages in sync receive_message #2937

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PYTHON-5906 Raise ProtocolError for malformed OP_COMPRESSED messages in sync receive_message #2937

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PYTHON-5906 Raise ProtocolError for malformed OP_COMPRESSED messages …
aclark4life Jul 16, 2026
8e6f0aa
Merge branch 'main' into PYTHON-5906-op-compressed-guard
aclark4life Jul 16, 2026
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4 changes: 4 additions & 0 deletions pymongo/network_layer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -775,6 +775,10 @@ def receive_message(
)
data: memoryview | bytes
if op_code == 2012:
if length <= 25:
raise ProtocolError(
f"Message length ({length!r}) not longer than standard OP_COMPRESSED message header size (25)"
)
op_code, _, compressor_id = _UNPACK_COMPRESSION_HEADER(receive_data(conn, 9, deadline))
data = decompress(receive_data(conn, length - 25, deadline), compressor_id)
else:
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15 changes: 15 additions & 0 deletions test/test_network_layer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,21 @@ def test_length_exceeds_max_raises(self):
with self.assertRaisesRegex(ProtocolError, "larger than server max"):
network_layer.receive_message(conn, request_id=None)

def test_compressed_length_too_small_raises(self):
# An OP_COMPRESSED frame with 16 < length <= 25 is malformed: it lacks
# room for the 9-byte compression sub-header plus payload. It must raise
# ProtocolError (not ValueError from a negative receive_data count).
for length in (17, 24, 25):
conn = _make_conn()
_mock_recv_into(
conn,
pack_msg_header(length=length, request_id=0, response_to=0, op_code=2012),
)
with self.assertRaisesRegex(
ProtocolError, "not longer than standard OP_COMPRESSED message header"
):
network_layer.receive_message(conn, request_id=None)

def test_unknown_opcode_raises(self):
conn = _make_conn()
_mock_recv_into(
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