this post was submitted on 10 Jul 2023
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FYI: Lemmy.world and other instances were hacked. Beehaw.org took itself down to mitigate risks (lemmy.world)
submitted 1 year ago* (last edited 1 year ago) by varsock to c/meta
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Drawing attention on this instance so Admins are aware and can address the propagating exploit.

EDIT: Found more info about the patch.

A more thorough recap of the issue.

GitHub PR fixing the bug: https://github.com/LemmyNet/lemmy-ui/pull/1897/files

If your instance has custom emojis defined, this is exploitable everywhere Markdown is available. It is NOT restricted to admins, but can be used to steal an admin's JWT, which then lets the attacker get into that admin's account which can then spread the exploit further by putting it somewhere where it's rendered on every single page and then deface the site.

If your instance doesn't have any custom emojis, you are safe, the exploit requires custom emojis to trigger the bad code branch.

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[–] object_Object 2 points 1 year ago* (last edited 1 year ago)

If lenny-ui is already using a JSX based library (InfernoJS), why not use it? I can't believe they construct HTML manually like that without a hint of escaping or stripping. Sure, many markdown renderers tell you to just slap it in __html or dangerouslySetInnerHtml but there are many that just parse the MD and let you render it with JSX!

I also can't believe there's no CSP that stopped this. Sure, it's a pain in the ass to configure with a nonce but this is literally the kind of thing it's made to block!