privacybadger
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EFForg
Detect and block tracking pixels
Identify and block the presence of tracking pixels in emails opened using the browser.
Can PB just blacklist known email tracker domains? Or should this be a toggle feature with a button and some indicator that it is working in emails? I found a list of trackers and am thinking you can stop 1x1 img from downloading if it comes from that domain?
Anyway, I want to work on this, but don't know which way PB wants to go re: blacklist vs visible toggle button
As a matter of principle, Privacy Badger must not maintain blacklists. This makes our job harder.
This feature would probably be a new kind of tracking heuristic where Privacy Badger would decide whether certain image resources were tracking pixels (tiny image dimensions with a non-trivial query string?) and then learn to block the domain (probably) the pixels are served from. This might be the same task as https://github.com/EFForg/privacybadger/issues/367#issuecomment-295314135.
I'm going to have a go at implementing this.
@ghostwords
non-trivial query string
What decides if a query string is non-trivial?
Possible conditions:
- number of parameters >= 3
- query string length > 120
- a parameter key containing "id"
Since there is so much overlap between #2088 and this, should we put a hold on this issue for now? @bcyphers already opened a PR.
What decides if a query string is non-trivial?
I was thinking of reusing either our HTML5 local storage entropy estimation function or the one for cookies.
The main technical obstacle with general-purpose pixel detection seems to be that there doesn't seem to be a way to get image dimensions from inside chrome.webRequest listeners. That might be fine, we could just go by querystring contents. I think #2088 is about taking querystring values and comparing them to known tracking values (retrieved from cookies).
Yeah, this is tough. I think we need to update the entropy function (per #2088), and after that it might be worth applying the same kind of heuristic to email pixels.
@ghostwords I think querystring contents alone are fine; a tracker is a tracker whether it's attached to an invisible pixel or a banner graphic. To be less invasive, we could just try stripping off high-entropy query params from image requests in emails.
Relevant study: "I never signed up for this! Privacy implications of email tracking" (from Proceedings on Privacy Enhancing Technologies 2018)