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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]

724 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] 72 points 1 year ago (17 children)

So what happened:

Someone posted a post.
The post contained some instruction to display custom emoji.
So far so good.
There is a bug in JavaScript (TypeScript) that runs on client's machine (arbitrary code execution?).
The attacker leveraged the bug to grab victim's JWT (cookie) when the victim visited the page with that post.
The attacker used the grabbed JWTs to log-in as victim (some of them were admins) and do bad stuff on the server.

Am I right?

I'm old-school developer/programmer and it seems that web is peace of sheet. Basic security stuff violated:

User provided content (post using custom emojis) caused havoc when processing (doesn't matter if on server or on client). This is lack of sanitization of user-provided-data.
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.
How the attacker got those JWTs? JavaScript sent them to him? Web browser sent them to him when requesting resources form his server? This is lack of site isolation, one web page should not have access to other domains, requesting data form them or sending data to them.
The attacker logged-in as admin and caused havoc. Again, this should not be possible, admins should have normal level of access to the site, exactly the same as normal users do. Then, if they want to administer something, they should log-in using separate username + password into separate log-in form and display completely different web page, not allowing them to do the actions normal users can do. You know, separate UI/applications for users and for admins.

Am I right? Correct me if I'm wrong.

Again, web is peace of sheet. This would never happen in desktop/server application. Any of the bullet points above would prevent this from happening. Even if the previous bullet point failed to do its job. Am I too naïve? Maybe.

Marek.

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

You're totally right. I just looked at my old jwt cookie and was susceptible to CSRF (cross site request forgery) by virtue of not having the SameSite flag being set. This has since been fixed, but it looks like there might still be changes pending as Javascript is currently able to read the cookie value (the HttpOnly flag is currently set to false, meaning that it is able to be accessed by the browser). While this isn't a major risk, it does increase the attack surface a bit.

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