1 yr. ago • 97%

(URGENT) Lemmy has an XSS vulnerability in the sidebar

cross-posted from: https://sh.itjust.works/post/923025

lemmy.world is a victim of an XSS attack right now and the hacker simply injected a JavaScript redirection into the sidebar.

It appears the Lemmy backend does not escape HTML in the main sidebar. Not sure if this is also true for community sidebars.

42 comments

This has nothing to do with XSS, it is a simple HTML injection vulnerability, and it can only be exploited by instance admins.

Also Lemmy.world appears to have been running a custom frontend so it’s hard to say how widespread the affects of this are.

32
- You seem to be following the situation closely. Could you please DM me on Matrix?
  
  9
- Worst case scenario, they can steal your Lemmy session, right?
  
  Which isn't super bad for a service like Lemmy. This isn't a social network, so most contact list scams would be useless.
  
  Edit: just read the targets were admins. That IS bad.
  
  1
  
  Lemmy isn't a social network? Seems to be one to me.
  
  3
It seems to have just gotten to Lemmy.blahaj.zone

15
I wonder if there is something the Lemmy.ca admins can do to disable the sidebar or put a workaround in to prevent this.

12
- At this point I'm monitoring inter-instance communications channels non stop even though I should be in bed. I will be temporarily removing admins that have not responded to my inquiry to confirm if they have 2FA authentication turned on as initial access appears to have been gained due to lack of 2FA.
  
  If there's anything additinal we can do, we will.
  
  37
  
  Good luck, and thanks for all your hard work. I don't know if you already saw this, but it looks like this might be the vector for the account compromise. If that's the case, I don't think 2FA is enough to protect, because it's exfiltrating the session cookies of someone already logged in. Seems like the precaution is for admins to avoid clicking any suspicious links. I realize the irony of sharing a link about this, but at least it's to a thread on this instance.
  
  https://lemmy.ca/post/1311411
  
  6
  
  Introduce minimum password complexity if there's a config option for it and force admins to reset passwords.
  
  2
I mean, if it's something that's editable only by admins of the instance, I'm not sure it constitutes a vulnerability, since admins can change the content to whatever they desire by definition.

7
- Wasn’t clear till further people commented that it was something only and admin could do. So I agree.
  
  5
  
  We have yet to confirm if a vulnerability exists in the sidebars that can be set by community mods.
  
  6
So, as an average, less-technical, Lemmy user (this is my backup for now).
What can or should I do to stay safe?

5
- https://lemmy.world/post/1290412?scrollToComments=true
  
  The affected instances are coming back and the vulnerability being mitigated. Apparently no personal data was compromised. So you should be fine.
  
  5
- Id use an app you trust for now
  
  On a site you have to sanitize your data, on a native app you'd have to go out of your way to render this kind of thing...wefwef/voyager is actually a web page (and they might or might not be sanitizing their inputs), the other top options are probably using libraries to do it, and data sanitation is pretty basic. Literally web dev 101. They'd have to choose a very full-featured rendering library that also entirely ignores security, or they'd have to have rolled their own
  
  At least now I know why my renderer has been so annoying about the warnings the last couple days...
  
  For any devs that read this - this is a great example of why you can't trust anything coming off a federated network. Type check and sanitize all your inputs, always. We need to get away from trust - this isn't a trustful situation
  
  Luckily, this was more of a warning than an actual attack - and there will be actual attacks. We have to be defensive - always - every time at every level.
  
  And Flemmy will be that, once I feel good releasing it (2 features left before I'm out of reasons to procrastinate). It'll be just me, always
  
  4
Only in its sidebar? :D

3
Beehaw completely shut down as a response

2
- While I respect their decision, I believe that's a over-reaction at this point and we will not be doing that, yet.
  
  5
for some reason I had to reset my password.

1
someone must be protesting lemmy if they are blocking the site and redirecting to NSFW

who has demonstrated use of that modus operandi ? /ponder

lmfaooooooo

-10
- why is your entire account dedicated to sucking reddit's asshole. do you like the taste of corporate shit?
  
  7
  
  Yeah it's so weird, why make an account here if he likes Reddit so much? We just want to have another place to have communities, that's why we left and stayed here. He should do the same, stay there and out of here if he hates this place so much.
  
  6

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