They don't need to. iCloud uploads plaintext content hashes of all files even when e2ee is turned on. They know all of the users that have certain files, even if each and every one of those users is using the opt-in e2ee of iCloud.
Normal iCloud allows Apple to scan everything serverside, natch. This is 99%+ of all iCloud users today.
However, regular hashes (SHA256 et al.) are too strict, and these hashes are mostly useless for this use case. The don't take variance in account what CSAM did. CSAM would have detected the image with different resolutions or slight modifications.
And your Mac sends all the hashes as well, whether they are in iCloud or not.
Could you elaborate? I didn't know Macs send local file hashes to Apple even if you don't use iCloud.
Gatekeeper sends all hashes of the opened executables/files.
https://lapcatsoftware.com/articles/catalina-executables.htm...
Also, the anti-virus sends, like Windows Defender et. all. They all do it to expand the storage of known files.
> macOS includes built-in antivirus technology called XProtect for the signature-based detection and removal of malware
https://support.apple.com/guide/security/protecting-against-...
Winnie the Pooh memes are shared verbatim.
Make one and share it and Apple knows who received it and when, and then who received it from them later, all with e2ee turned on and no iMessage.
Do you have a source for that claim? This is interesting.