Patched code sample

import os

# Since CVE-2025-56005 is a fictional vulnerability, this code demonstrates
# a plausible fix based on the provided description. The fix involves
# completely removing the unsafe, undocumented `picklefile` parameter and its
# associated `pickle.load()` logic from the `yacc()` function.

# A simplified representation of the vulnerable yacc function would have
# contained a code block like this:
#
# if picklefile:
#     with open(picklefile, 'rb') as f:
#         # VULNERABLE: Unsafe deserialization leads to RCE
#         table = pickle.load(f)
#     # ... proceed to use the loaded table
#
# The fixed version below removes this entire code path.


def yacc(module=None, method='LALR', debug=False, **kwargs):
    """
    A representation of the securely patched yacc() function.

    THE FIX for CVE-2025-56005:
    The vulnerable 'picklefile' parameter has been completely removed from the
    function's logic. Any code path that previously accepted a filename and
    deserialized it with `pickle.load()` has been eliminated to prevent
    Remote Code Execution.
    """

    # 1. Check for the deprecated parameter to prevent silent failures and
    #    to explicitly inform users of the security change. Instead of
    #    processing it, the function now raises an error.
    if 'picklefile' in kwargs:
        raise ValueError(
            "'picklefile' parameter is no longer supported due to a severe "
            "security vulnerability (CVE-2025-56005). Loading parser tables "
            "from external pickle files is insecure and has been removed."
        )

    # 2. The rest of the function proceeds as normal, generating the parser
    #    table safely in memory without deserializing any untrusted data.
    #    The dangerous `pickle.load()` call does not exist in this function.
    print("FIXED: Generating parser table safely in memory.")
    parser_table = "/* This represents a safely generated parser table */"
    print("FIXED: Parser table generation complete.")

    # Note: While loading tables via pickle is removed, saving a newly generated
    # table might still be a valid (and safe) feature, as the data being
    # serialized is trusted. The vulnerability was in the loading/deserialization part.
    # For example:
    # with open('parsetab.py', 'w') as f:
    #     f.write(parser_table)

    return parser_table


# --- Demonstration of the Fix ---

if __name__ == '__main__':
    print("--- 1. Calling the fixed function the intended, safe way ---")
    yacc()
    print("-" * 50)

    print("\n--- 2. Attempting to use the removed 'picklefile' parameter ---")
    # A dummy malicious file for the demonstration.
    # In a real attack, this file would contain a malicious pickle payload.
    malicious_filename = "malicious_payload.pkl"
    with open(malicious_filename, "w") as f:
        f.write("This is a placeholder for a malicious pickle object.")

    try:
        # This call will now fail with a ValueError instead of executing code.
        print(f"Calling yacc() with picklefile='{malicious_filename}'...")
        yacc(picklefile=malicious_filename)
    except ValueError as e:
        print(f"\nSUCCESS: The fix worked as expected.")
        print(f"The function correctly raised an error: {e}")
        print("The insecure code path was not executed.")

    # Clean up the dummy file.
    os.remove(malicious_filename)