How to protect from CSAM flooding (similar to Swatting)

Solution 1:

There's no attack to mitigate really as the premise behind the attack is flawed.

Apple's new CSAM detection will work in iCloud Photos - not in iCloud Messages. Someone sending you CSAM as a swatting attack will not trigger the CSAM detection. It doesn't matter if it is sent by Apple Messages, Facebook Messenger, WhatsApp or Instagram.

If you, the user, decides that you want to keep the CSAM you have been attacked with and start saving it to iCloud Photos - instead of reporting it to the authorities - then you have a problem. However the problem is probably not the CSAM detection, but rather something worse.