this post was submitted on 30 Aug 2023
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Lemmy

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Everything about Lemmy; bugs, gripes, praises, and advocacy.

For discussion about the lemmy.ml instance, go to [email protected].

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PSA: You can upload images to a Lemmy instance without anyone knowing (lemmy.ca)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]
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EDIT

TO EVERYONE ASKING TO OPEN AN ISSUE ON GITHUB, IT HAS BEEN OPEN SINCE JULY 6: https://github.com/LemmyNet/lemmy/issues/3504

June 24 - https://github.com/LemmyNet/lemmy/issues/3236

TO EVERYONE SAYING THAT THIS IS NOT A CONCERN: Everybody has different laws in their countries (in other words, not everyone is American), and whether or not an admin is liable for such content residing in their servers without their knowledge, don't you think it's still an issue anyway? Are you not bothered by the fact that somebody could be sharing illegal images from your server without you ever knowing? Is that okay with you? OR are you only saying this because you're NOT an admin? Different admins have already responded in the comments and have suggested ways to solve the problem because they are genuinely concerned about this problem as much as I am. Thank you to all the hard working admins. I appreciate and love you all.

ORIGINAL POST

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.

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[–] [email protected] 122 points 1 year ago (3 children)

Perhaps someone should create a script to purge orphan images

[–] [email protected] 46 points 1 year ago (1 children)

Seems like the logical fix

[–] [email protected] 57 points 1 year ago (2 children)

The logical fix would be to delete them automatically when unused for longer than let's say 24 hours. That should be in the lemmy code, and we should not depend on 3rd party utilities to do that.

[–] [email protected] 11 points 1 year ago (1 children)

You can submit a patch upstream

[–] [email protected] 38 points 1 year ago (3 children)

Not everyone is a developer. Users are allowed to point out issues without working on fix themselves.

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[–] [email protected] 12 points 1 year ago* (last edited 1 year ago) (1 children)

Or, just tighten up the api such that uploaded pictures have a relatively short TTL unless they become attached to a post or otherwise linked somewhere.

A script is a fine stopgap measure, but we should try to treat the cause wherever possible, instead of simply addressing the symptom.

[–] [email protected] 6 points 1 year ago* (last edited 1 year ago) (2 children)

What's the practical difference? In both cases you're culling images based on whether they're orphaned or not.

If you're suggesting that the implementation be based on setting individual timers instead of simply validating the whole database at regular intervals, consider whether or not the complexity of such a system is actually worth the tradeoff.

"Complexity comshmexity", you might say. "Surely it's not a big deal!". Well... what about an image that used to belong to a valid post that later got deleted? Guess you have to take that edge case into account and add a deletion trigger there as well! But what if there were other comments/posts on the same instance hotlinking the same image? Guess you have to scan the whole DB every time before running the deletion trigger to be safe! Wait... wasn't the whole purpose of setting this up with individual jobs to avoid doing a scripted DB scan?

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[–] [email protected] 8 points 1 year ago

Very much needed.

[–] [email protected] 101 points 1 year ago* (last edited 1 year ago)

FYI to all admins: with the next release of pict-rs, it should be much easier to detect orphaned images, as the pict-rs database will be moved to postgresql. I am planning to build a hashtable of "in-use" images by iterating through all posts and comments by lemm.ee users (+ avatars and banners of course), and then I will iterate through all images in the pict-rs database, and if they are not in the "in-use" hash table, I will purge them.

Of course, Lemmy can be improved to handle this case better as well!

[–] [email protected] 43 points 1 year ago (1 children)

Did you opened an issue on github?

You are wording this as a clickbait news article.

You find an issue, you report it to the right channel, you notify it. Good. This is how software development work, with active community reporting issues.

But why using such tone?

[–] [email protected] 33 points 1 year ago (8 children)

I'm not on GitHub. Nor is a lot here. I'm wording it this way so the issue gets the attention it deserves. Anyway, everybody already knows about this but nobody understood the consequences. Same reason why there's no option to disable image caching. These issues should have been addressed the moment image uploading was made available in Lemmy. It was just overlooked because of how tiny the platform was then.

It's funny because last month Mastodon CSAM was a hot topic in the Fediverse and people were being defensive about it. Look where we are now. Has Mastodon addressed the CSAM issue? Did they follow the recommendations made by that paper? I don't think so. There wouldn't be an open GitHub issue about it. Will Lemmy be like Mastodon or will it addressed the concerns of its users?

[–] [email protected] 23 points 1 year ago* (last edited 1 year ago) (1 children)

Creating a product of any size is about planning.

If you notify here, your information will be lost in 2 days. People forget, and move on to the next hot topic. Relevant stakeholders might very well completely miss this post, because they are not 24/7 on lemmy.

The way to make it more relevant is going in the place where the planning is done, i.e. Github for lemmy. Open an issue there, explain the problem and describe possible solution. Come back to lemmy, link the issue and ask people to react to it (i.e. show it is relevant for them).

This is the best way to obtain what you ask. Social media platforms are too broad and fuzzy for tracking real issues.

This is also why you see a lot of work is done on performances of sql of lemmy backend, because most issues in the past on github concerned that.

This is my suggestion. If you really care about this being implemented, open a ticket on github and follow the discussion there. If you see there is not enough traction ask help to fellow lemmings.

Suggestions for the github issue are:

  • be very specific
  • be polite
  • suggest solutions

If your solution is good, great, if not, people are more willing to think about a problem to show stranger on the internet they are wrong

[–] [email protected] 6 points 1 year ago (7 children)

Feel free to open the issue on my behalf. I am not a software developer. You seem to know more about this. I'm just reminding people something that I and many others have observed months ago.

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[–] [email protected] 38 points 1 year ago (8 children)

I’m an instance administrator, what the fuck do I do?

There's one more option. The awesome @[email protected] has made this tool to detect and automatically remove CSAM content from a pict-rs object storage.

https://github.com/db0/lemmy-safety

[–] [email protected] 24 points 1 year ago (1 children)

This is a nice tool but orphaned images still need to be purged. Mentioned on the other thread that bad actors can upload spam to fill up object storage space.

[–] [email protected] 7 points 1 year ago

That is also very true. I think better tooling for that might come with the next pict-rs version, which will move the storage to a database (right now it's in an internal ky-value storage). Hopefully that will make it easier to identify orphaned images.

[–] [email protected] 5 points 1 year ago (8 children)

I tried getting this to run in a container, but I was unable to access my GPU in the container. Does anyone have any tips on doing that?

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[–] [email protected] 22 points 1 year ago (5 children)

Pedo trolls will be the death of Lemmy, you heard it here first!

[–] [email protected] 17 points 1 year ago

Which is why we need to act now.

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[–] [email protected] 22 points 1 year ago (1 children)

'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.

How? I have checked, and there doesn't seem to be any way to see the photos on my server.

I actually shut down pictrs entirely on my instance. Running pictrs in its current state is criminally negligent imo.

[–] [email protected] 18 points 1 year ago (1 children)

They are stored in the pctrs folder. They don't have file extensions but are viewable with many image programs.

[–] [email protected] 15 points 1 year ago

Oh, I see. I only use command line on my server, so I didn't realize they were actual photos. Thanks!

[–] [email protected] 17 points 1 year ago (2 children)

FYI this requires a JWT so if registrations are closed on your instance you don't have to worry

[–] [email protected] 7 points 1 year ago

This is for public instances.

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[–] [email protected] 16 points 1 year ago (2 children)

A lot of web software does this (Github and Gmail for example). I like it but always thought it could be abused.

[–] [email protected] 14 points 1 year ago

You mean Gmail drafts? I know from at least one case where criminals used this, they shared the Gmail account password and messaged each other only via the drafts function. So technically there was never a mail send.

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[–] [email protected] 15 points 1 year ago (2 children)

Wasn't facebook also found to store images that were uploaded but not posted? This is just a resource leak . I can't believe no one has mentioned this phrase yet. I'm more concerned about DoS attacks that fill up the instance's storage with unused images. I think the issue of illegal content is being blown out of proportion. As long as it's removed promptly (I believe the standard is 1 hour) when the mods/admins learn about it, there should be no liabilities. Otherwise every site that allows users to post media would be dead by now.

[–] [email protected] 11 points 1 year ago

I'm a pentester and security consultant. From my point of view, this vulnerability has more impact than just a resource leak or DOS. We all know how often CSAM or other illegal material is uploaded to communities here as actual posts (where hundreds of viewers run into it to report it). Now imagine them uploading it and spreading it like this, and only the admin can catch it if they goes out of their way to check it?

I wouldn't call this a high risk issue for sure. But a significant security risk regardless.

[–] [email protected] 8 points 1 year ago

Whether it's illegal content or storage-filling DoS attacks, the issue needs to be addressed.

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