Lemmy.world (and some others) were hacked

Ruud@lemmy.worldmod to Lemmy.World Announcements@lemmy.world – 2321 points –

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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JavaScript (TypeScript) has access to cookies (and thus JWT). This should be handled by web browser, not JS. In case of log-in, in HTTPS POST request and in case of response of successful log-in, in HTTPS POST response. Then, in case of requesting web page, again, it should be handled in HTTPS GET request. This is lack of using least permissions as possible, JS should not have access to cookies.

JavaScript needs access to the cookies, they are the data storage for a given site.
To protect them, the browser silos them to the individual site that created them, that's why developers haven't been able to easily load cross domain content for years, to mitigate XSS attacks.
The security relies on the premise that the only valid source of script is the originating domain.
The flaw here was allowing clients to add arbitrary script that was displayed to others.
You're dead right that only the way to fix this is to do away with JavaScript access to certain things, but it will require a complete refactor of how cookies work.
I haven't done any web dev in a few years, this might even be a solved problem by now and we are just seeing an old school implementation. 🤷

this might even be a solved problem by now

Yes, it is called HttpOnly and is decided by the server who is sending the cookie to you in HTTP response header. I believe there are also HTTPS-only cookies that when received via HTTPS, cannot be used from HTTP, but I cannot find it right now.