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.
Security is crazy hard and having perfect security is impossible. Kudos to the dev team for resolving this so quickly.
It makes me think I should see about contributing. I’m not an expert in security flaws or pen testing, but having an extra set of eyes checking for vulnerabilities doesn’t hurt.
Plus, in my experience, the vulnerabilities to watch out for are code that the developers didn’t write. Updating packages usually isn’t a problem until it’s discovered a major version update is necessary looks at Spring angrily
In my opinion, the project would benefit from static vulnerability scanning. Low hanging fruit like this XSS would have definitely been flagged.
Most of those providers even give it out for free for open source projects. So it wouldn’t hurt.