Fediverse

Masquerading a normal looking link for another one, usually phishing, malware, clones loaded with ads.

Like, lets say I post something like

https://www.google.com

And also have my instance intercept it to provide Google's embed preview image, and it federates that with other instances.

Now, for everyone it would look like a Google link, but you get Microsoft Google instead.

I could also actually post a genuine Google link but make the preview go somewhere else completely, so people may see the link goes where they expect even when putting the mouse over it, but then they end up clicking the preview for whatever reason. Bam, wrong site. Could also be a YouTube link and embed but the embed shows a completely different preview image, you click on it and get some gore or porn instead. Fake headlines, whatever way you can think of to abuse this, using the cyrillic alphabet, whatever.

People trust those previews in a way, so if you post a shortened link but it previews like a news article you want to go to, you might click the image or headline but end up on a phony clone of the site loaded with malware. Currently, if you trust your instance you can actually trust the embed because it's generated by your instance.

On iMessage, it used that the sender would send the embed metadata, so it was used for a zero click exploit by sending an embed of a real site but with an attachment that exploited the codec it would be rendered with.