“One of the major changes in iOS 14 is the introduction of a new, tightly sandboxed “BlastDoor” service which is now responsible for almost all parsing of untrusted data in iMessages (for example, NSKeyedArchiver payloads).”
Apple rebuilt iMessage’s parsing inside a sandbox called BlastDoor and re-randomizes the shared cache when it detects an attack. It took a Google researcher to explain what changed. Citizen Lab had just linked hacked journalists’ phones to a suspected NSO Group zero-click iMessage exploit. Apple’s best security work ships with almost no documentation.