Fingerprinting is unhealthy. It’s a time period that refers to build up sufficient metadata a couple of person that you would be able to primarily work out who they’re. JavaScript has entry to all types of fingerprinting prospects, which then mixed with the IP tackle that the server has entry to, means fingerprinting is all too frequent.
You don’t usually consider CSS as being a fingerprinting vector although, and thus “secure” in that approach. However Oliver Brotchie has documented an thought that enables for some extent of fingerprinting with CSS alone.
Consider all of the @media queries we have now. We are able to check for pointer sort with any-pointer. Think about that for every worth, we request a very distinctive background-image from a server. If that picture was requested, we all know these @media queries had been true. We are able to begin to fingerprint with one thing like this:
.pointer {
background-image: url(‘/unique-id/pointer=none’)
}
@media (any-pointer: coarse) {
.pointer {
background-image: url(‘/unique-id/pointer=coarse’)
}
}
@media (any-pointer: effective) {
.pointer {
background-image: url(‘/unique-id/pointer=effective’)
}
}
Mix that with the truth that we will check for a darkish mode choice with prefers-color-scheme, the fingerprint will get a bit clearer. In actual fact, it’s the present draft for CSS person desire media queries that Oliver is most involved about:
Not solely will the upcoming draft make this methodology scalable, however it would additionally improve its precision. Presently, with out different means, it’s laborious to conclusively hyperlink each request to a particular customer as the one possible solution to decide their origin, is to group the requests by the IP tackle of the connection. Nonetheless, with the brand new draft, by producing a randomised string and interpolating it into the URL tag for each customer, we will precisely determine all requests from stated customer.
There are tons extra. We are able to make media queries which can be 1px aside and request a background picture for every, completely guessing the customer’s window measurement. There are most likely a dozen or extra unique media queries which can be not often used, however are helpful particularly to fingerprinting with CSS. Mix that with @helps queries for all types of issues to primarily guess the precise browser. And mix that with the basic strategy of testing for set up of particular native fonts, and you’ve got a half-decent fingerprinting machine.
@font-face
font-family: ‘some-font’
src: native(some font), url(‘some/url/some-font’)
.some-font
font-family:’some-font’
The generated CSS to do it’s large (right here’s the Sass to generate it), however apparently it’s closely diminished as soon as we will use customized properties in URLs.
I’m not closely anxious about it, largely as a result of I don’t disable JavaScript and JavaScript is a lot extra extensively able to fingerprinting already. Plus, there are already different forms of CSS safety vulnerabilities, from studying visited hyperlinks (which browsers have addressed), keylogging, and person generated inline kinds, amongst others that people have identified in one other article on the subject.
However Oliver’s analysis on fingerprinting is admittedly good and worthy of a glance by everybody who is aware of extra about net safety than I do.
CSS-Primarily based Fingerprinting initially printed on CSS-Methods
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