cross-posted from: https://lemmy.dbzer0.com/post/4500908

In the past months, there’s a been a issue in various instances where accounts would start uploading blatant CSAM to popular communities. First of all this traumatizes anyone who gets to see it before the admins get to it, including the admins who have to review to take it down. Second of all, even if the content is a link to an external site, lemmy sill caches the thumbnail and stores it in the local pict-rs, causing headaches for the admins who have to somehow clear that out. Finally, both image posts and problematic thumbnails are federated to other lemmy instances, and then likewise stored in their pict-rs, causing such content to be stored in their image storage.

This has caused multiple instances to take radical measures, from defederating liberaly, to stopping image uploads to even shutting down.

Today I’m happy to announce that I’ve spend multiple days developing a tool you can plug into your instance to stop this at the source: pictrs-safety

Using a new feature from pictr-rs 0.4.3 we can now cause pictrs to call an arbitary endpoint to validate the content of an image before uploading it. pictrs-safety builds that endpoint which uses an asynchronous approach to validate such images.

I had already developed fedi-safety which could be used to regularly go through your image storage and delete all potential CSAM. I have now extended fedi-safety to plug into pict-rs safety and scan images sent by pict-rs.

The end effect is that any images uploaded or federated into your instance will be scanned in advance and if fedi-safety thinks they’re potential CSAM, they will not be uploaded to your image storage at all!

This covers three important vectors for abuse:

  • Malicious users cannot upload CSAM to for trolling communities. Even novel GenerativeAI CSAM.
  • Users cannot upload CSAM images and never submit a post or comment (making them invisible to admins). The images will be automatically rejected during upload
  • Deferated images and thumbnails of CSAM will be rejected by your pict-rs.

Now, that said, this tool is AI-driven and thus, not perfect. There will be false positives, especially around lewd images and images which contain children or child-topics (even if not lewd). This is the bargain we have to take to prevent the bigger problem above.

By my napkin calculations, false positive rates are below 1%, but certainly someone’s innocent meme will eventually be affected. If this happen, I request to just move on as currently we don’t have a way to whitelist specific images. Don’t try to resize or modify the images to pass the filter. It won’t help you.

For lemmy admins:

  • pictrs-safety contains a docker-compose sample you can add to your lemmy’s docker-compose. You will need to your put the .env in the same folder, or adjust the provided variables. (All kudos to @Penguincoder@beehaw.org for the docker support).
  • You need to adjust your pict-rs ENVIRONMENT as well. Check the readme.
  • fedi-safety must run on a system with GPU. The reason for this is that lemmy provides just a 10-seconds grace period for each upload before it times out the upload regardless of the results. A CPU scan will not be fast enough. However my architecture allows the fedi-safety to run on a different place than pictrs-safety. I am currently running it from my desktop. In fact, if you have a lot of images to scan, you can connect multiple scanning workers to pictrs-safety!
  • For those who don’t have access to a GPU, I am working on a NSFW-scanner which will use the AI-Horde directly instead and won’t require using fedi-safety at all. Stay tuned.

For other fediverse software admins

fedi-safety can already be used to scan your image storage for CSAM, so you can also protect yourself and your users, even on mastodon or firefish or whatever.

I will try to provide real-time scanning in the future for each software as well and PRs are welcome.

Divisions by zero

This tool is already active now on divisions by zero. It’s usage should be transparent to you, but do let me know if you notice anything wrong.

Support

If you appreciate the priority work that I’ve put in this tool, please consider supporting this and future development work on liberapay:

https://liberapay.com/db0/

All my work is and will always be FOSS and available for all who need it most.

  • ABluManOnLemmy@feddit.nlEnglish
    493·
    1 year ago

    Be careful with this though. I think I remember some jurisdictions require server owners not to delete CSAM and report it instead. Verify that you aren’t obligated to keep it before deleting it

    • HTTP_404_NotFound@lemmyonline.comEnglish
      522·
      1 year ago

      not upload CSAM to for trolling communities. Even novel GenerativeAI CSAM. Users cannot upload CSAM images and never submit a post or comment (making them invisible to admins). The images will be automatically rejected during upload

      There wouldn’t be anything to delete, as it would have never been saved with this.

      • shagie@programming.devEnglish
        164·
        1 year ago

        https://www.law.cornell.edu/uscode/text/18/2258A

        (a) Duty To Report.—
        (1) In general.—
        (A) Duty.—In order to reduce the proliferation of online child sexual exploitation and to prevent the online sexual exploitation of children, a provider—
        (i) shall, as soon as reasonably possible after obtaining actual knowledge of any facts or circumstances described in paragraph (2)(A), take the actions described in subparagraph (B); and
        (ii) may, after obtaining actual knowledge of any facts or circumstances described in paragraph (2)(B), take the actions described in subparagraph (B).
        (B) Actions described.—The actions described in this subparagraph are—
        (i) providing to the CyberTipline of NCMEC, or any successor to the CyberTipline operated by NCMEC, the mailing address, telephone number, facsimile number, electronic mailing address of, and individual point of contact for, such provider; and
        (ii) making a report of such facts or circumstances to the CyberTipline, or any successor to the CyberTipline operated by NCMEC.

        …

        (e) Failure To Report.—A provider that knowingly and willfully fails to make a report required under subsection (a)(1) shall be fined—
        (1) in the case of an initial knowing and willful failure to make a report, not more than $150,000; and
        (2) in the case of any second or subsequent knowing and willful failure to make a report, not more than $300,000.

        Check with a lawyer if blocking an upload that your server has access to because of suspected CSAM constitutes “actual knowledge or any facts or circumstances”.

        • HTTP_404_NotFound@lemmyonline.comEnglish
          374·
          1 year ago

          HEY LOCAL PD OFFICE,

          SOMEONE TRIED TO UPLOAD SOME POTENTIALLY CHILD PORN TO MY LEMMY INSTANCE.

          No… I don’t have an IP for who uploaded it.

          Sorry, I don’t know where it came from. It just got federated across the fediverse to me.

          No… I don’t have the content either, it doesn’t get saved.

          Sorry… I guess I really don’t have any details at all for you.

      • Obinice@lemmy.worldEnglish
        102·
        1 year ago

        So the image never touches the server side, even in RAM, it always remains only on the client machine, and it’s checked there?

        If so, then this could be a pretty neat tidy way to deal with this issue, otherwise the image is on the server, even if you “delete it real fast” or such, and I imagine then you’d still need to be in compliance with the law regarding saving and reporting it.

        • Deiv@lemmy.caEnglish
          16·
          1 year ago

          Did you read the post? The image is sent to an endpoint that has a hosted AI solution that checks it

          It 100% touches the server, it’s just not stored anywhere and gets blocked

    • explodicle@local106.comEnglish
      5·
      1 year ago

      Does that leave open a possible attack, in which the attacker can just fill up the server’s hard drive with AI-generated CSAM?

      • ABluManOnLemmy@feddit.nlEnglish
        3·
        1 year ago

        I think that if, in good faith, the person is unable to accept more CSAM due to the fact that their hard drive is full, there isn’t an issue. The intent of the law is that, it someone knows something is CSAM, they need to report it. I don’t think the government is going to come hard on Lemmy server owners unwittingly receiving CSAM through federation (though they certainly would want them to report and take down the CSAM on their servers)

    • deFrisselle@lemmy.sdf.orgEnglish
      3·
      1 year ago

      It’s not getting uploaded, so nothing to keep
      That’s the point The Kiddy Porn never hits the server There might be an argument for the scanner cache to be saved for later reporting to authorities Thank is assuming the scanner also logs the account, ip, time, etc of the upload