Note: This post now archived and as such no longer works
This is possible because Lemmy doesn’t proxy external images but instead loads them directly. While not all that bad, this could be used for Spy pixels by nefarious posters and commenters.
Note, that the only thing that I willingly log is the “hit count” visible in the image, and I have no intention to misuse the data.
Nice example!
I think proxying everything through lemmy would have a pretty big bandwidth/scalability impact. I expect the lemmy clients dont send any unique user info on these image requests so not sure how useful it would be as a spy pixel? Maybe I’m missing something :-)
Notably, this allows remote parties to associate your IP address with your interests, as revealed by the Lemmy communities that you browse.
One way is for the image host to use the HTTP Referer field. (Standards-respecting web browsers pass the URL of the web page being viewed to the server hosting the image.)
Another way is by posting an image with a unique URL.
Even if Referer is withheld and the image is not unique, the image host can still do basic fingerprinting of your client’s request header and your OS’s TCP quirks, and associate that fingerprint with your IP address.
An option for Lemmy to proxy media would be very helpful. Small instances could perhaps disable it, although they might not need to, since the additional load would scale with the number of users on that instance.
Were you expecting otherwise? Loading an external image is no different than loading an external website with images. Lemmy and reddit are link aggregators, not proxies. Having to proxy everything would run a significant bandwidth for instance admin who are often paying out of pocket for hosting.
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How do you get an image to run code? I guess I somehow missed something important in website development.
Edit: I saw that you said you’re using Pillow to actually render the image from code. That’s neat! …and scary
Share source code? I’m curious
It’s just a simple Flask server. I parse the user-agent using the
user_agentsPython library, apply some conditionals upon the result, render the image using Pillow and send it to the user.
Oh neat, Jerboa doesn’t identify itself. Cool.
Same on Sync (You are viewing this from an unknown (mobile?) client)
And on infinity (You are viewing this from Android)
I get “unknown (mobile?) client” using Jerboa
I’m fine with this. Instances shouldn’t proxy or cache images because it opens instance owners to a lot more liability than text. A client side setting to not load images in comments by default is better.
VPN using Librewolf user checking in. This post got nothing on me.
Yeah, I’m using Mullvad with misc DNS blockers enabled so it has nothing on me ᕕ( ᐛ )ᕗ
Man, I remember I scared the crap out of trolls on Reddit when we started arguing over DM, and I added a link to a meme that tracked their IP and system info (without them knowing ofc). Let’s just say they went AFK quickly after that. Good times!
I got mobile client from Liftoff.
Holy shit. How do we avoid this? VPN?
I would say a user agent spoofer would be more useful for this particular image. The Mozilla team recommends User-Agent Switcher and Manager for Firefox users.
Next DNS Blocks it apparently.
Wow! But mine didn’t. Which filter lists are you using?
Well… Basically all…
It’s not nearly as nefarious as people seem to think. Effectively all applications that access web resources send along what they are and basic platform information.
This is part of how the application asks for content in a way that it can handle
It does a little to let you be tracked, but there are other techniques that are far more reliable for that purpose.
Lemmy clients should really include an option to group or only show the first instance of a link for cases like this; where the same link is posted to multiple places.
All these people correcting the result effectively giving useful data to improve data collection and detection methods.
So what is happening if I don’t see an image?
it is because the website providing the image is overloaded and cannot create an image.
You just have to reload the image and eventually you will see one.
