cross-posted from: https://lemmy.ca/post/4273025
You can upload images to a Lemmy instance without anyone knowing that the image is there if the admins are not regularly checking their pictrs database.
To do this, you create a post on any Lemmy instance, upload an image, and never click the “Create” button. The post is never created but the image is uploaded. Because the post isn’t created, nobody knows that the image is uploaded.
You can also go to any post, upload a picture in the comment, copy the URL and never post the comment. You can also upload an image as your avatar or banner and just close the tab. The image will still reside in the server.
You can (possibly) do the same with community icons and banners.
Why does this matter?
Because anyone can upload illegal images without the admin knowing and the admin will be liable for it. With everything that has been going on lately, I wanted to remind all of you about this. Don’t think that disabling cache is enough. Bad actors can secretly stash illegal images on your Lemmy instance if you aren’t checking!
These bad actors can then share these links around and you would never know! They can report it to the FBI and if you haven’t taken it down (because you did not know) for a certain period, say goodbye to your instance and see you in court.
Only your backend admins who have access to the database (or object storage or whatever) can check this, meaning non-backend admins and moderators WILL NOT BE ABLE TO MONITOR THESE, and regular users WILL NOT BE ABLE TO REPORT THESE.
Aren’t these images deleted if they aren’t used for the post/comment/banner/avatar/icon?
NOPE! The image actually stays uploaded! Lemmy doesn’t check if the images are used! Try it out yourself. Just make sure to copy the link by copying the link text or copying it by clicking the image then “copy image link”.
How come this hasn’t been addressed before?
I don’t know. I am fairly certain that this has been brought up before. Nobody paid attention but I’m bringing it up again after all the shit that happened in the past week. I can’t even find it on the GitHub issue tracker.
I’m an instance administrator, what the fuck do I do?
Check your pictrs images (good luck) or nuke it. Disable pictrs, restrict sign ups, or watch your database like a hawk. You can also delete your instance.
Good luck.
Note, my tools is the only solution that exists (currently) for this in regards to csam
https://github.com/db0/lemmy-safety
Appreciate your work.
Not hosting images is a far better solution, and also exists.
What’s the best away for be to disable the pictrs directory? Is there a setting to flip in my instance?
Your contributions to the Lemmy ecosystem are much appreciated 🙏🏼
I hate how everything is a double edged sword, because this is now also the perfect tool for making sure your CSAM doesn’t trip the filter. Also, it uses CLIP so a simple obfuscation overlay would render it useless.
can you elaborate on what an obfuscation overlay is?
Any of filter or image processing technique that fools machine vision.
Example: https://sandlab.cs.uchicago.edu/fawkes/
This could be done with any kind of image or detail, not just faces.
I don’t think random trolls like that would be be that sophisticated, but in any case we can deal with that once we get to that point.