I almost made the rash, uninformed decision to close up shop on lemmy.world and move my community to another instance. Luckily I did some further reading, and yeah, unless whatever other instance I jumped ship to was also patched I would have just been wasting my time since this is a vulnerability in the Lemmy code and affects all instances until the admins apply a bandaid/the code is fixed.
XSS injection in custom emojis.
Essentially, custom emojis used by instances could allow a malicious actor to execute arbitrary code on clients that saw the emoji (within the scope of the website).
There is speculation about links and other vectors, but those aren't clear yet. But the successful attacks have been tracked back to emojis.
The emojis aren't federated, so it would only affect users of that instance that viewed the emoji during the attack.
The injected script (as it was being execute as part of the client UI, thus trusted) had access to the client cookies for the instance.
It would steal the JWT tokens stored in the cookies and send them to a 3rd party site.
Tokens of Admins were then used by the attackers to deface the sites.
It's unclear what user data would have been vulnerable during this time - still being investigated.
There is a high likelihood that this is a GDPR reportable incident.
The fix is for admins to delete all custom emojis via the database, then rotate JWT secrets.
Rotating the secrets invalidates all users JWTs, so everyone has to log in again. This also invalidates the stolen JWTs.
On that note: does anybody know when or even if lemmy.world will be up again? Right now I'm using an alt account but I've got a main one and a community on .world and I couldn't really find any information on how it's going over there.