Patched code sample

import pickle
import pickletools
import trace
import io
import os

# The CVE-2025-71352 vulnerability is hypothetical. This code demonstrates
# how a fix for the described flaw in a security scanner like `picklescan`
# would be implemented. The fix involves updating a denylist of dangerous
# functions to include `trace.Trace.runctx`.

def fixed_scanner(pickle_data: bytes):
    """
    Simulates a security scanner with the vulnerability fix applied.

    It inspects pickle opcodes for dangerous `GLOBAL` imports, including the one
    described in the CVE. An unfixed scanner would lack 'trace.runctx' in its
    denylist and would fail to detect the payload.
    """
    # The fix is to add 'trace.runctx' to the list of known dangerous functions.
    # The pickle `GLOBAL` opcode resolves `trace.Trace.runctx` to module 'trace'
    # and name 'runctx'.
    DANGEROUS_GLOBALS = {
        "os.system",
        "subprocess.run",
        # The line below represents the fix for CVE-2025-71352.
        "trace.runctx",
    }

    try:
        for opcode, arg, _ in pickletools.genops(pickle_data):
            if opcode.name == "GLOBAL":
                # The arg is in the format "module\nname"
                full_name = arg.replace("\n", ".")
                if full_name in DANGEROUS_GLOBALS:
                    print(f"FIX APPLIED: Detected dangerous global '{full_name}'")
                    return False # Unsafe
    except Exception:
        # Malformed pickle data could cause errors
        return False # Unsafe

    print("Scan complete: No known dangerous globals found.")
    return True # Safe


if __name__ == "__main__":
    # 1. Create a malicious pickle payload using the `trace.Trace.runctx` function.
    # This payload would bypass a scanner that is not aware of this vector.
    command = "echo '[DEMO] Malicious code executed via trace.Trace.runctx'"
    malicious_obj = (
        trace.Trace.runctx,
        (trace.Trace(count=0), command, {}, {}),
    )
    malicious_data = pickle.dumps(malicious_obj)

    print("--- Scanning malicious pickle data with the FIXED scanner ---")
    is_safe = fixed_scanner(malicious_data)

    if not is_safe:
        print("\nThe scanner correctly identified the payload as unsafe.")
        print("Execution was blocked by the scanner's detection.")
    else:
        # This block would execute if the scanner were NOT fixed.
        print("\nScanner failed to detect the payload. Executing pickle.load():")
        # The following line is the dangerous operation.
        pickle.loads(malicious_data)