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fix: check WebSocket MASK bit before reading masking key (RFC 6455 §5.2) #14170

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Merged
xxnet merged 1 commit into from
May 12, 2026
+15 −5
Merged

fix: check WebSocket MASK bit before reading masking key (RFC 6455 §5.2) #14170

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20 changes: 15 additions & 5 deletions code/default/lib/noarch/simple_http_server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -281,15 +281,25 @@ def WebSocket_receive_worker(self):
if h is None or len(h) == 0:
break

length = ord(h[1]) & 127
# RFC 6455 §5.2: bit 7 of byte 2 is the MASK flag.
# If MASK=1 a 4-byte masking key follows the (extended) length;
# if MASK=0 the payload begins immediately — no key is present.
is_masked = bool(ord(h[1]) & 0x80)
length = ord(h[1]) & 0x7F
if length == 126:
length = struct.unpack(">H", self.rfile.read(2))[0]
elif length == 127:
length = struct.unpack(">Q", self.rfile.read(8))[0]
masks = [ord(byte) for byte in self.rfile.read(4)]
decoded = ""
for char in self.rfile.read(length):
decoded += chr(ord(char) ^ masks[len(decoded) % 4])

if is_masked:
masks = [ord(byte) for byte in self.rfile.read(4)]
decoded = "".join(
chr(ord(char) ^ masks[i % 4])
for i, char in enumerate(self.rfile.read(length))
)
else:
decoded = "".join(chr(ord(c)) for c in self.rfile.read(length))

try:
self.WebSocket_on_message(decoded)
except Exception as e:
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