cross-posted from: https://lemmy.cat/post/6385
It is currently possible, through Lemmy's API, to create accounts automatically and without limit if verification by email address or captcha is not activated. I'd advise you to activate one or both of them NOW!
After registering x number of accounts (currently I could do thousands), all you have to do is list all the existing communities for each of the account to publishes one new post per community, or more. I'll leave you to picture the mess.
(I apologise to the administrators of sh.itjust.works, I should have done the test with my own server.)
This is indeed not an ideal situation, but I guess on most instances this isn't possible. I agree instances should require a captcha of some sort for signing up.
Unfortunately lemmy devs removed captchas recently https://github.com/LemmyNet/lemmy/issues/2922 so email verification and/or rate limiting is probably the only real option for protection.