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Lemmy.world (and some others) were hacked (lemmy.world)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

720 comments fedilink hide all child comments

While I was asleep, apparently the site was hacked. Luckily, (big) part of the lemmy.world team is in US, and some early birds in EU also helped mitigate this.

As I am told, this was the issue:

There is an vulnerability which was exploited
Several people had their JWT cookies leaked, including at least one admin
Attackers started changing site settings and posting fake announcements etc

Our mitigations:

We removed the vulnerability
Deleted all comments and private messages that contained the exploit
Rotated JWT secret which invalidated all existing cookies

The vulnerability will be fixed by the Lemmy devs.

Details of the vulnerability are here

Many thanks for all that helped, and sorry for any inconvenience caused!

Update While we believe the admins accounts were what they were after, it could be that other users accounts were compromised. Your cookie could have been 'stolen' and the hacker could have had access to your account, creating posts and comments under your name, and accessing/changing your settings (which shows your e-mail).

For this, you would have had to be using lemmy.world at that time, and load a page that had the vulnerability in it.

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[–] [email protected] 23 points 1 year ago (1 children)

If a valid browser token gets stolen like in this case, then MFA won't do much good because the stolen token will already have been authenticated. Linus Tech Tips experienced the same thing recently, you can check out their channel.

[–] [email protected] 7 points 1 year ago (2 children)

That makes sense, thanks so much - there's a few good explanations here which really help! Would it be right in saying that all affected servers should be logging off all users - some have but not sure if all.

[–] riskable 7 points 1 year ago* (last edited 1 year ago)

The fix is to force the use of a new JWT encryption key which--when set--would immediately invalidate all existing user cookies, forcing all users to relogin.

Lemmy has a few weaknesses related to their use of JWT in cookies that need to be addressed... The biggest one being that they use the same secret key for all user cookies (every user should have their own unique session key). I'm pretty sure that if they implemented that the scope of this vulnerability would be drastically reduced (but I haven't looked at the precise mechanism of the vulnerability yet).

They also need to provide tools in the GUI for admins and users to invalidate all issued sessions (cookies) and a mechanism for regularly rotating session secrets (the cookie currently lasts for a year and even if the session token gets regenerated it'll still use the same secret).

They also need to make the expiration times configurable so that security-focused servers can set short expiration times. Related, they need to force the use of unique secrets for every session (even if it's the same user using different devices/apps).

[–] [email protected] 6 points 1 year ago

I guess that would depend on the specific case. If you physically went on my computer to steal my token or infected my computer with a virus to do it then we can assume that no other tokens have been compromised. But if the malicious actor has managed to steal tokens from the actual server (which seems to be the case here) and not the client then yes, as the admin I would certainly require that everyone log in again as a safety measure.