

I don’t think dansup was in the wrong here. Yes, it’s a security issue I suppose, but the problem lies within the underlying protocol. Any server you interact with can ignore any privacy markers you add to posts, you’re just not supposed to do that.
Whether this is a 0day depends on what you expect out of the Fediverse. If you treat it like a medium where every user or server has the potential to be hostile, like you probably should, this is a mere validation logic bug. If you treat it like the social media many of its servers are trying to be, it’s a gross violation of your basic privacy expectations.
Building trust is hard. It’s easier to trust a few companies than to trust a million unknown servers. It’s why I prefer Wikipedia over amazingnotskgeneratedatalltopicalinformarion.biz when I’m looking up simple facts.
Furthermore, Facebook isn’t selling data directly. At least, not if they’re following the law. They got caught doing and fined doing that once and it’s not their main mode of operation. Like Google, their data is their gold mine, selling it directly would be corporate suicide. They simply provide advertisers with spots to put an ad, but when it comes to data processing, they’re doing all the work before advertisers get a chance to look at a user’s profile.
On the other hand, scraping ActivityPub for advertisers would be trivial. It’d be silly to go through the trouble to set up something like Threads if all you want is information, a basic AP server that follows ever Lemmy community and soaks up gigabytes an hour can be written as a weekend project.
Various Chinese data centers are scraping the hell out of my server, and they carry referer headers from other Fediverse servers. I’ve blocked half of East Asia and new IP addresses keep popping up. Whatever data you think Facebook may be selling, someone else is already selling based on your Fediverse behaviour. Whatever Petal Search and all the others are doing, I don’t believe for a second they’re being honest about it.
Most Fediverse software defaults to federation and accepting inbound follow requests. At least, Mastodon, Lemmy, GoToSocial, Kbin, and one of those fish named mastodonlikes did. Profiles are often public by default too. The vulnerability applies to a large section of the Fediverse default settings.
I’d like to think people would switch to the Fediverse despite the paradigm shift. The privacy risks are still there if there’s only one company managing them, so I’d prefer it if people used appropriate tools for sharing private stuff. I think platforms like Circles (a Matrix-based social media system) which leverage encryption to ensure nobody can read things they shouldn’t have been able to, are much more appropriate. Perhaps a similar system can be laid on top of ActivityPub as well (after all, every entity already has a public/private key pair).