extras.example.net is still third-party to awesome.example.org.
The tracking company has no way of knowing that an HTTP request to extras.example.net is from the same user as an HTTP request to awesome.example.org.
If you were operating the tracking company, how would you try to determine the same user is behind both requests? Happy to be proven wrong, but I don't believe it's possible with third-party cookie protections in place.
1. awesome.example.org would add a CNAME record that resolves tracking-you.example.org to the server referenced by evil.com
2. awesome.other.net would add a CNAME record that resolves tracking-you.other.net to the server referenced by evil.com
3. etc everywhere on the internet
Because these are CNAME, DNS hides all of this from the browser and it just sees the resolved address and the original requested name.
So tracking-you.example.org and tracking-you.other.net both now think the server controlled by evil.com is first-party. evil.com now gets all the first-party cookies. In the past they would have only got third-party cookies and the first-party cookies wouldn't be seen by evil.com.
But it gets worse because evil.com is also tracking you (it's what they're explicitly doing) so they can link users across the sites. This means evil.com has all it needs to spoof you cross-site because they now have all the first-party auth tokens. Unless you diligently never use the sites simultaneously and remember to log out between using websites. But even if you did, they can still do anything they want as you while you're logged in to the site.
So, yeah. It actually looks like a disaster and we're super screwed.
That's not the case. Both example.com and other.net are likely to be generating completely unique auth tokens.
example.org and other.net can certainly both coordinate with evil.com to manually share more detail (e.g. the current user is UserA@gmail.com), but if that's the threat then browsers have no chance at offering protection.
Then, when evil.com receives a different auth token for the same user visiting other.net, how does evil.com know that new auth token correlates to the same user on example.org?
This is the third-party identity linking that's now impossible for evil.com to accomplish independently. They need other.net and example.org to share some common information (like an email address) to make the link. For logged out users, it should be impossible without resorting to fingerprinting.
This was Firefox and Safari's entire reason d'etre for launching Total Cookie Protection and Intelligent Tracking Protection. I don't believe CNAME cloaking overcomes their protections, or at the very least, I don't see where this paper explains an attack vector.
The bottom line is that evil.com would not be asking sites to install CNAME tricks in their domains if evil.com cannot leverage those tricks to track users across sites. That should be obvious.
This is the leap I believe is incorrect. The paper doesn't explain how CNAME cloaking helps evil.com track users across sites. It says that it does, but it doesn't actually explain the attack vector.
It is far more plausible to me that CNAME tricks are being added so that evil.com can track a user on an individual site. When uBlock Origin is putting a hard block on all traffic to evil.com, there's still quite a bit to be gained by shifting evil.com to evil.foo.com if that means requests start succeeding again.
Another poster said something similar here: https://news.ycombinator.com/item?id=26349987
Isn't cookie validity selected by the site? A diligent site could setup subdomains to isolate the tracking cookines. Say, .awesome.example.org rather than .example.org. tracking-you.example.org wouldn't match anymore. But then it's a third-party cookie again and ad-block could just keep cookie whitelists for .awesome.example.org and throw any other .example.org cookies out.
Of course ads.example.com could just as well have A/AAAA records pointing to the same ad server, which would neutralize any attempt to infer separate origins based on CNAME records. It would just be slightly more difficult to administer since the owner of example.com would need to update their DNS records whenever the ad server's IP address changed—but that could be automated, and the IPs are probably mostly static anyway.
DNS was thought out from the beginning so you could split it anywhere you wanted to delegate things, and you can also delegate with CNAME too.
I'd welcome a security model that does not use origins. It's doable, but the origin trick was a convenient way to enforce some security measures bolted on as an after thought without breaking much the compatibility.
You have the explanation right. But your hypothetical future dystopia is actually the world of today. (-:
You can specify the domain when you set cookies, but it is limited to the domain your page is on (and browsers have lists of domain parts that are banned so you can’t for instance set cookies on co.uk )
Yes, that's right. I'm making the assumption that letting the request succeed at all is on the losing side of the battle.
For me, I know I'm 100% trackable across the internet with my IP address (it hasn't changed in 2 years) and my screen resolution (the only 4k monitors behind that IP). If I don't block the request in the first place, the tracking company fingerprints my browser and sets that as a cookie.
The reason I say we're completely screwed is that I think we'll see all kinds of dirty tricks. Ex: auth = ads under the header and auth.example.net is actually a tracking domain. That's much harder to prevent than sending ads.example.com to a black hole.
CNAMEs and first-party cookie access aren't helping networks link identities across sites in Firefox and Safari - at this point they're stuck relying on browser fingerprinting. And as you point out, fingerprinting can be quite effective, especially for people on static IPs :|
This paper is claiming that CNAMEs are evading the protections offered by Safari and Firefox but that's just not the case. Or at least, the paper hasn't explained how.