What is the Intent extra injection vulnerability in Android, and what validation must developers perform before using Intent extras in security-sensitive decisions?

• A.A. An exported component that reads Intent extras and uses them for authorization (e.g., extras.getBoolean('isAdmin')) can be exploited by any caller who constructs an Intent with the expected key set to an attacker-chosen value; developers must never trust Intent extras for authorization - use server-side or cryptographic verification instead
• B.B. Intent extra injection is exclusive to implicit Intents; explicit Intents with a fully qualified component name are immune
• C.C. The vulnerability only applies to String extras; boolean and int extras are validated by the Android framework
• D.D. Intent extras are signed by the PackageManager at dispatch, preventing tampering by the sender