cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. Starting in version 38.0.0 and prior to version 42.0.4, if pkcs12.serialize_key_and_certificates is called with both a certificate whose public key did not match the provided private key and an encryption_algorithm with hmac_hash set (via PrivateFormat.PKCS12.encryption_builder().hmac_hash(...), then a NULL pointer dereference would occur, crashing the Python process. This has been resolved in version 42.0.4, the first version in which a ValueError is properly raised.
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.