UPDATE: The latest RC version of Lemmy-ui (0.18.2-rc.2) contains fixes for the issue, but if you believe you were vulnerable, you should still rotate your JWT secret after upgrading! Read below for instructions. Removing custom emoji is no longer necessary after upgrading.
Original post follows:
This post is intended as a central place that admins can reference regarding the XSS incident from this morning.
What happened?
A couple of the bigger Lemmy instances had several user accounts compromised through stolen authentication cookies. Some of these cookies belonged to admins, these admin cookies were used to deface instances. Only users that opened pages with malicious content during the incident were vulnerable. The malicious content was possible due to a bug with rendering custom emojis.
Stolen cookies gave attackers access to all private messages and e-mail addresses of affected users.
Am I vulnerable?
If your instance has ANY custom emojis, you are vulnerable. Note that it appears only local custom emojis are affected, so federated content with custom emojis from other instances should be safe.
I had custom emojis on my instance, what should I do?
This should be enough to mitigate now:
- Remove custom emoji
DELETE FROM custom_emoji_keyword;
DELETE FROM custom_emoji;
- Rotate your JWT secret (invalidates all current login sessions)
-- back up your secret first, just in case
SELECT * FROM secret;
-- generate a new secret
UPDATE secret SET jwt_secret = gen_random_uuid();
- Restart Lemmy server
If you need help with any of this, you can reach out to me on Matrix (@sunaurus:matrix.org) or on Discord (@sunaurus)
Legal
If your instance was affected, you may have some legal obligations. Please check this comment for more info: https://lemmy.world/comment/1064402
This bug also needs to be fixed so that a user logging out / changing password actually correctly invalidates their JWT token: https://github.com/LemmyNet/lemmy/issues/3364
I suspect that last night even if an admin knew their account was compromised, they probably couldn’t do anything about it without DB access.
Okay it is insane that that issue is 2 weeks old and was not prioritized and because of that the hacker was gifted 2 weeks to prepare an attack.
I love Lemmy and am grateful for the work of the devs. But I see huge issues with the LemmyNet governance.
Previously it was captchas that were removed because one of the two main devs had a strong personal belief that captchas are “useless” and wanted to impose that belief upon everyone, which then led to an enormous wave of bots with the 0.18.0 as captchas were removed. I’m glad he was then convinced that he was wrong to remove them and then took steps to revert that decision, but it took too long and many instances suffered performance problems by being forced to stay with the 0.17.6 version because it had captchas.
Right now the same thing happens again with issues about security being left unanswered for two weeks. I believe right now all feature developments should be paused and a security audit of the whole code base should be the #1 priority.
This is just very bad. Proper governance and prioritization would have avoided exposing minors to lemon party porn and other disgusting content.
I can only imagine how helpless the admin whose account was compromised felt if she didn’t have access to the database to invalidate those tokens, and it could have been prevented if that issue was properly prioritized.
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