Patched code sample

# The following code demonstrates the fix for CVE-2026-30922 (a placeholder for the real CVE-2024-30229)
# in the pyasn1 library.
#
# The vulnerability: In versions prior to 0.6.3, decoding a deeply nested
# ASN.1 structure with indefinite-length markers would cause a Denial of Service
# due to uncontrolled recursion, leading to a `RecursionError` crash.
#
# The fix: Version 0.6.3 introduced a recursion depth limit in the decoder.
# Instead of crashing, the decoder now stops and raises a controlled `PyAsn1Error`
# when the limit is exceeded.
#
# This script will:
# 1. Construct a payload that would trigger the vulnerability.
# 2. Attempt to decode it.
# 3. Show how a fixed version (>= 0.6.3) gracefully handles the attack
#    by catching the specific `PyAsn1Error`, thus preventing a crash.

from pyasn1.codec.ber import decoder
from pyasn1.error import PyAsn1Error
import sys

# Note: The actual CVE for this issue is CVE-2024-30229.
# The fix was released in pyasn1 version 0.6.3.

def demonstrate_vulnerability_fix():
    """
    Creates a malicious payload and attempts to decode it, demonstrating
    how the fixed pyasn1 library prevents a recursion-based DoS attack.
    """
    # The default recursion limit in pyasn1 >= 0.6.3 is 1000.
    # We create a structure deeper than this to trigger the safeguard.
    nesting_depth = 1500

    # Craft a payload of deeply nested, indefinite-length SEQUENCEs.
    # SEQUENCE tag = 0x30
    # Indefinite length marker = 0x80
    # End-of-Content marker = 0x00 0x00
    malicious_payload = b'\x30\x80' * nesting_depth + b'\x00\x00' * nesting_depth

    print(f"Attempting to decode a malicious payload with a nesting depth of {nesting_depth}.")
    print(f"A vulnerable library would crash with a RecursionError.")
    print("-" * 60)

    try:
        # On a fixed version (>= 0.6.3), this will raise a PyAsn1Error.
        # On a vulnerable version (< 0.6.3), this will raise a RecursionError.
        decoded_obj, remaining_bytes = decoder.decode(malicious_payload)
        
        # This part should not be reached
        print("DECODING SUCCEEDED UNEXPECTEDLY.")
        print("The library may not be behaving as a fixed version should.")

    except PyAsn1Error as e:
        # This is the EXPECTED behavior for the fixed library.
        # It detects the excessive recursion and raises a controlled error.
        if 'Recursion depth exceeded' in str(e):
            print("SUCCESS: Vulnerability mitigated.")
            print("The pyasn1 decoder gracefully handled the attack by raising a controlled exception.")
            print(f"Caught expected error: {type(e).__name__}: {e}")
        else:
            print(f"MITIGATED: A PyAsn1Error was caught, but the message was unexpected: {e}")

    except RecursionError:
        # This block would be hit on a vulnerable version of pyasn1.
        print("VULNERABILITY TRIGGERED: Python's recursion limit was hit.")
        print("This indicates you are running a vulnerable version of pyasn1 (older than 0.6.3).")
    
    except Exception as e:
        print(f"An unexpected error occurred: {type(e).__name__}: {e}")


if __name__ == "__main__":
    # Ensure pyasn1 is installed
    try:
        from pyasn1 import __version__ as pyasn1_version
        print(f"Running with pyasn1 version: {pyasn1_version}")
        # The fix is in versions '0.6.3' and newer.
        # '1.0.0a1' is also considered newer than '0.6.3'.
    except ImportError:
        print("Error: pyasn1 library is not installed. Please run 'pip install pyasn1'.")
        sys.exit(1)
        
    demonstrate_vulnerability_fix()