Hey folks!

I made a short post last night explaining why image uploads had been disabled. This was in the middle of the night for me, so I did not have time to go into a lot of detail, but I’m writing a more detailed post now to clear up where we are now and where we plan to go.

What’s the problem?

As shared by the lemmy.world team, over the past few days, some people have been spamming one of their communities with CSAM images. Lemmy has been attacked in various ways before, but this is clearly on a whole new level of depravity, as it’s first and foremost an attack on actual victims of child abuse, in addition to being an attack on the users and admins on Lemmy.

What’s the solution?

I am putting together a plan, both for the short term and for the longer term, to combat and prevent such content from ever reaching lemm.ee servers.

For the immediate future, I am taking the following steps:

1) Image uploads are completely disabled for all users

This is a drastic measure, and I am aware that it’s the opposite of what many of our users have been hoping, but at the moment, we simply don’t have the necessary tools to safely handle uploaded images.

2) All images which have federated in from other instances will be deleted from our servers, without any exception

At this point, we have millions of such images, and I am planning to just indiscriminately purge all of them. Posts from other instances will not be broken after the deletion, the deleted images will simply be loaded directly from other instances.

3) I will apply a small patch to the Lemmy backend running on lemm.ee to prevent images from other instances from being downloaded to our servers

Lemmy has always loaded some images directly from other servers, while saving other images locally to serve directly. I am eliminating the second option for the time being, forcing all images uploaded on external instances to always be loaded from those servers. This will somewhat increase the amount of servers which users will fetch images from when opening lemm.ee, which certainly has downsides, but I believe this is preferable to opening up our servers to potentially illegal content.

For the longer term, I have some further ideas:

4) Invite-based registrations

I believe that one of the best ways to effectively combat spam and malicious users is to implement an invite system on Lemmy. I have wanted to work on such a system ever since I first set up this instance, but real life and other things have been getting in the way, so I haven’t had a chance. However, with the current situation, I believe this feature is more important then ever, and I’m very hopeful I will be able to make time to work on it very soon.

My idea would be to grant our users a few invites, which would replenish every month if used. An invite will be required to sign up on lemm.ee after that point. The system will keep track of the invite hierarchy, and in extreme cases (such as spambot sign-ups), inviters may be held responsible for rule breaking users they have invited.

While this will certainly create a barrier of entry to signing up on lemm.ee, we are already one of the biggest instances, and I think at this point, such a barrier will do more good than harm.

5) Account requirements for specific activities

This is something that many admins and mods have been discussing for a while now, and I believe it would be an important feature for lemm.ee as well. Essentially, I would like to limit certain activities to users which meet specific requirements (maybe account age, amount of comments, etc). These activities might include things like image uploads, community creation, perhaps even private messages.

This could in theory limit creation of new accounts just to break rules (or laws).

6) Automated ML based NSFW scanning for all uploaded images

I think it makes sense to apply automatic scanning on all images before we save them on our servers, and if it’s flagged as NSFW, then we don’t accept the upload. While machine learning is not 100% accurate and will produce false positives, I believe this is a trade-off that we simply need to accept at this point. Not only will this help against any potential CSAM, it will also help us better enforce our “no pornography” rule.

This would potentially also allow us to resume caching images from other instances, which will improve both performance and privacy on lemm.ee.

With all of the above in place, I believe we will be able to re-enable image uploads with a much higher degree of safety. Of course, most of these ideas come with some significant downsides, but please keep in mind that users posting CSAM present an existential threat to Lemmy (in addition to just being absolutely morally disgusting and actively harmful to the victims of the abuse). If the choice is between having a Lemmy instance with some restrictions, or not having a Lemmy instance at all, then I think the restrictions are the better option.

I also would appreciate your patience in this matter, as all of the long term plans require additional development, and while this is currently a high priority issue for all Lemmy admins, we are all still volunteers and do not have the freedom to dedicate huge amounts of hours to working on new features.

As always, your feedback and thoughts are appreciated, so please feel free to leave a comment if you disagree with any of the plans or if you have any suggestions on how to improve them.

  • @PriorProject@lemmy.world
    1•1 year ago

    I’m not sure I follow the suggestion.

    • NCMEC, the US-based organization tasked with fighting CSAM, has already partnered with a list of groups to develop CSAM detection tools. I’ve already linked to an overview of the resulting toolsets in my original comment.
    • The datasets used to develop these tools are private, but that’s not an oversight. The datasets are… well… full of CSAM. Distributing them openly and without restriction would be contrary to NCMEC’s mission and to US law, so they limit the downside by partnering only with serious/capable partners who are able to commit to investing significant resources to developing and long-term maintaining detection tools, and who can sign onerous legal paperwork promising to handle appropriately the access they must be given to otherwise illegal material to do so.
    • CSAM detection tools are necessarily a cat and mouse game of CSAM producers attempting to evade detection vs detection experts trying to improve detection. In such a race, secrecy is a useful… if costly… tool. But as a result, NCMEC requires a certain amount of secrecy from their partners about how the detection tools work and who can run them in what circumstances. The goal of this secrecy is to prevent CSAM producers from developing test suites that allow them to repeatedly test image manipulation strategies that retain visual fidelity but thwart detection techniques.

    All of which is to say…

    … seems like law enforcement would have such a data set and seems they should of course allow tools to be trained on it. seems but who knows? might be worth finding out.)

    Law enforcement DOES have datasets, and DO allow tools to be trained on them… I’ve linked the resulting tools. They do NOT allow randos direct access to the data or tools, which is a necessary precaution to prevent attackers from winning the circumvention race. A Red Hat or Mozilla scale organization might be able to partner with NCMEC or another organization to become a detection tooling partner, but db0, sunaurus, or the Lemmy devs likely cannot without the support of a large technology org with a proven track record or delivering and maintaining successful/impactful technology products. This has the big downside of making a true open-source detection tool more or less impossible… but that’s a well-understood tradeoff that CSAM-fighting orgs are not likely to change as the same access that would empower OSS devs would empower CSAM producers. I’m not sure there’s anything more to find out in this regard.