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CNAME-tracking is a relatively new phenomenon, where ad marketing firms (led by Salesforce and Adobe) are convincing sites to tweak CNAME records in order to ge

by spenvo 6y ago

CNAME-tracking is a relatively new phenomenon, where ad marketing firms (led by Salesforce and Adobe) are convincing sites to tweak CNAME records in order to get browsers to send a domain's cookie data (yes, security implications here are severe). This tracking method has become increasingly popular with tens of thousands of high-traffic sites utilizing it, and browsers have no built-in defenses against it. A more at-length layman's explanation can be found here, starting on page 8 https://www.grc.com/sn/sn-808-notes.pdf https://www.grc.com/sn/sn-808-notes.pdf But as the title hits upon, there is one countermeasure that uBlock Origin has implemented for its Firefox extension. But unlike Firefox, Chrome does not provide robust enough extension APIs for the countermeasure to work there. Chrome users are currently completely susceptible to having private cookie data stolen on thousands of high-traffic sites. Even in the case of this countermeasure though, it does seem insufficient as it's essentially a whack-a-mole game. Browsers must prioritize shutting this down in a more foolproof way, and I can't imagine an easy way to do that.

thrwwy0304 6y ago
This is false. Safari and Firefox both have strong third party cookie protections that prevent linking identities across different sites. At this point, the only way an ad network can tell that the same user is on Website A and Website B is if both site owners tell the ad network the current user's email address or other common identifier. If both sites are opting into this, CNAME protections won't do anything.
- thrwwy0304 6y ago
  The cookie protections I'm referencing are Safari's "Intelligent Tracking Protection" and Firefox's "Total Cookie Protection." Efforts would be much better spent trying to stop fingerprinting, trying to convince Chrome to add third party cookie protection, or lobbying for regulation.
  - rodgerd 6y ago
    The third of those. This isn't a technical problem, it's a "greedy maw of the surveillance economy" problem.
- donmcronald 6y ago
  The CNAMEs change it to a same site / first party relationship. It says it right in the article summary. I assume the way it works is that instead of `tracking.example.com` where everyone can block `example.com`, they have users set up CNAMEs instead. So you get: - extras.example.net --> tracking company IP behind a huge CDN - awesone.example.org --> tracking company IP behind a huge CDN The sites are different, but when you visit them you're hitting the tracking servers who get to see you hit both sites. Even worse, they can set cookies on the the domain, which is why someone else said there are security implications. I've been saying it for years. Eventually everything will appear to be first party and hitting huge CDN IPs. It's easy to do right now already. Go read the Cloudflare blog article on proxying Google Fonts via Workers. Then think about the Cloudflare Apps and how easy it would be to build an app that rotated first party CNAMES and used Workers to dynamically rewrite HTML to proxy the tracking to ad companies. TLDR; We're super screwed.
  - thrwwy0304 6y ago
    We're not super screwed. 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.
    - fluidcruft 6y ago
      Based on reading the links someone posted, my understanding is that the way this CNAME stuff works is: 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.
- jrochkind1 6y ago
  You are talking about the rules for javascript access to cookies, or other rules for "cross-domain cookies". The rules for "block third-party cookies" features are different than these, and are browser-specific rather than bound by a standard. I believe that both Chrome and Firefox will not block cookies from a subdomain of the same base domain as "third-party". Although I'm not totally sure where to find this documented. I think if they did, it would break many more sites than "block third-party cookies" do now.
  - thrwwy0304 6y ago
    The way tracking used to work is: 1. UserA visits foo.com which embeds a script from evil.com. When the script is requested, evil.com sees there's no tracking cookie for this user yet, so it drops one. 2. When evil.com was loaded, the Referer header showed the request was coming from foo.com. EvilCo adds an entry that UserA visited foo.com. 3. UserA now visits bar.com which also embeds a script from evil.com. Now, the tracking cookie from Step 1 already exists, so it's sent with the request to load the script from evil.com. 4. evil.com looks at the Cookie and Referer header, and adds an entry that UserA has visited bar.com. --- Now, what Firefox and Safari have done, is they've made it impossible for ANY third party to access their cookies while a user is visiting a different site. I completely understand that evil.com is promoting itself to first-party by routing under evil.foo.com and evil.bar.com, and that allows it to set and receive cookies on those hosts, but that alone isn't enough to break out of the new browser protections. In this new world, evil.foo.com and evil.bar.com are still third party to each other, and so there's no way to sync identifiers between them, even though they're both operated by evil.com. To sync identities across evil.foo.com and evil.bar.com, EvilCo is forced to do some kind of browser fingerprinting, or to rely on the operators of foo.com and bar.com to manually share additional data about the user. --- Source - I've tried it! Run two separate domains and see if you can get the same unique identifier in cookies on both domains. The only workarounds are OAuth2 and the Storage Access API - both of which require explicit user permission.
    - jrochkind1 6y ago
      Thanks for trying to explain. What I'm not following is that you say: > In this new world, evil.foo.com and evil.bar.com are still third party to each other, and so there's no way to sync identifiers between them, even though they're both operated by evil.com. But in your original 1-4 description, foo.com and evil.com already were third-party to each other. So apparenty that was not a barrier? Your original description doesn't actually mention mention any shared identifiers between evil.com and foo.com, just that evil.com would use a referer header to see that the rquest was coming from foo.com. Won't this work exactly the same way with evil.foo.com and evil.bar.com? Your original 1-4 stopped working because FF and Chrome stopped letting evil.com set cookies at all when loaded from foo.com. That is the restriction that broke 1-4 (it wasn't other restrictions that were in place when 1-4 was working fine), and that is the restriction you get around with evil.foo.com, restoring the situation where your 1-4 steps worked. What am I missing?
jaytaylor 6y ago
Appreciate you raising awareness about this! Seems like one more nail in the coffin for Chrome versus alternatives which have a higher degree of people's true best interests at heart. As a side note, this really deserves a blog post or singular site/page that explains the issue in a simple enough way so the word can spread.
- random5634 6y ago
  Another nail? I’ve been hearing that for 10 years - be interesting to see if chrome usage drops a lot. With edge now chromium based I’ve been seeing usage go up not down
  - shawnz 6y ago
    Anecdotally, I switched to FF after the manifest v3 changes were announced.
    - croes 6y ago
      Chrome is the new IE. Everybody knows it's bad, but it's standard.
      - minikites 6y ago
        Except web developers love Chrome, which is why Google might actually win control of the web.
        jimbob45 6y ago
        Amen. FF’s dev tools are like Windows 95 to Chrome’s Windows 7.
        temp667 6y ago
        Yeah, from where I sit Chrome is the absolute first target, regardless of how many nails are being nailed into its coffin. There is some thought that if Apple opens up iOS a bit Chrome could make more headway there as well. Numbers I've heard are Chrome - 60%, Firefox < 5%.
dang 6y ago
The submitted title ("CNAME tracking's a disaster. uBlock Origin blocks it in FF. Chrome users are SOL") broke the site guidelines. Accounts that do that eventually lose submission privileges, so please don't do that. It looks like a fine submission otherwise! "Please use the original title, unless it is misleading or linkbait; don't editorialize." https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- spenvo 6y ago
  Thanks dang, sorry—I blanked out on that rule and will try to remember moving forward (I think I’ve made this mistake before). Cheers
  - dang 6y ago
    Appreciated!
tinus_hn 6y ago
How can browsers defend against sites giving away their own private cookies to trackers? They could just as well send the data from the server side.
XzetaU8 6y ago
"Chrome users are currently completely susceptible to having private cookie data stolen on thousands of high-traffic sites" Not true, sure it's a workaround solution but with frogeye's block list [0] and uBO you're pretty much covered on Chrome regarding CNAME-tracking [0]:Geoffrey Frogeye's block list of first-party trackers https://hostfiles.frogeye.fr/ https://hostfiles.frogeye.fr/

by spenvo 6y ago

thrwwy0304 6y ago

This is false. Safari and Firefox both have strong third party cookie protections that prevent linking identities across different sites. At this point, the only way an ad network can tell that the same user is on Website A and Website B is if both site owners tell the ad network the current user's email address or other common identifier. If both sites are opting into this, CNAME protections won't do anything.

thrwwy0304 6y ago
The cookie protections I'm referencing are Safari's "Intelligent Tracking Protection" and Firefox's "Total Cookie Protection." Efforts would be much better spent trying to stop fingerprinting, trying to convince Chrome to add third party cookie protection, or lobbying for regulation.
- rodgerd 6y ago
  The third of those. This isn't a technical problem, it's a "greedy maw of the surveillance economy" problem.
donmcronald 6y ago
The CNAMEs change it to a same site / first party relationship. It says it right in the article summary. I assume the way it works is that instead of `tracking.example.com` where everyone can block `example.com`, they have users set up CNAMEs instead. So you get: - extras.example.net --> tracking company IP behind a huge CDN - awesone.example.org --> tracking company IP behind a huge CDN The sites are different, but when you visit them you're hitting the tracking servers who get to see you hit both sites. Even worse, they can set cookies on the the domain, which is why someone else said there are security implications. I've been saying it for years. Eventually everything will appear to be first party and hitting huge CDN IPs. It's easy to do right now already. Go read the Cloudflare blog article on proxying Google Fonts via Workers. Then think about the Cloudflare Apps and how easy it would be to build an app that rotated first party CNAMES and used Workers to dynamically rewrite HTML to proxy the tracking to ad companies. TLDR; We're super screwed.
- thrwwy0304 6y ago
  We're not super screwed. 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.
  - fluidcruft 6y ago
    Based on reading the links someone posted, my understanding is that the way this CNAME stuff works is: 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.
jrochkind1 6y ago
You are talking about the rules for javascript access to cookies, or other rules for "cross-domain cookies". The rules for "block third-party cookies" features are different than these, and are browser-specific rather than bound by a standard. I believe that both Chrome and Firefox will not block cookies from a subdomain of the same base domain as "third-party". Although I'm not totally sure where to find this documented. I think if they did, it would break many more sites than "block third-party cookies" do now.
- thrwwy0304 6y ago
  The way tracking used to work is: 1. UserA visits foo.com which embeds a script from evil.com. When the script is requested, evil.com sees there's no tracking cookie for this user yet, so it drops one. 2. When evil.com was loaded, the Referer header showed the request was coming from foo.com. EvilCo adds an entry that UserA visited foo.com. 3. UserA now visits bar.com which also embeds a script from evil.com. Now, the tracking cookie from Step 1 already exists, so it's sent with the request to load the script from evil.com. 4. evil.com looks at the Cookie and Referer header, and adds an entry that UserA has visited bar.com. --- Now, what Firefox and Safari have done, is they've made it impossible for ANY third party to access their cookies while a user is visiting a different site. I completely understand that evil.com is promoting itself to first-party by routing under evil.foo.com and evil.bar.com, and that allows it to set and receive cookies on those hosts, but that alone isn't enough to break out of the new browser protections. In this new world, evil.foo.com and evil.bar.com are still third party to each other, and so there's no way to sync identifiers between them, even though they're both operated by evil.com. To sync identities across evil.foo.com and evil.bar.com, EvilCo is forced to do some kind of browser fingerprinting, or to rely on the operators of foo.com and bar.com to manually share additional data about the user. --- Source - I've tried it! Run two separate domains and see if you can get the same unique identifier in cookies on both domains. The only workarounds are OAuth2 and the Storage Access API - both of which require explicit user permission.
  - jrochkind1 6y ago
    Thanks for trying to explain. What I'm not following is that you say: > In this new world, evil.foo.com and evil.bar.com are still third party to each other, and so there's no way to sync identifiers between them, even though they're both operated by evil.com. But in your original 1-4 description, foo.com and evil.com already were third-party to each other. So apparenty that was not a barrier? Your original description doesn't actually mention mention any shared identifiers between evil.com and foo.com, just that evil.com would use a referer header to see that the rquest was coming from foo.com. Won't this work exactly the same way with evil.foo.com and evil.bar.com? Your original 1-4 stopped working because FF and Chrome stopped letting evil.com set cookies at all when loaded from foo.com. That is the restriction that broke 1-4 (it wasn't other restrictions that were in place when 1-4 was working fine), and that is the restriction you get around with evil.foo.com, restoring the situation where your 1-4 steps worked. What am I missing?

jaytaylor 6y ago

Appreciate you raising awareness about this! Seems like one more nail in the coffin for Chrome versus alternatives which have a higher degree of people's true best interests at heart. As a side note, this really deserves a blog post or singular site/page that explains the issue in a simple enough way so the word can spread.

random5634 6y ago
Another nail? I’ve been hearing that for 10 years - be interesting to see if chrome usage drops a lot. With edge now chromium based I’ve been seeing usage go up not down
- shawnz 6y ago
  Anecdotally, I switched to FF after the manifest v3 changes were announced.
  - croes 6y ago
    Chrome is the new IE. Everybody knows it's bad, but it's standard.
    - minikites 6y ago
      Except web developers love Chrome, which is why Google might actually win control of the web.
      - jimbob45 6y ago
        Amen. FF’s dev tools are like Windows 95 to Chrome’s Windows 7.
      - temp667 6y ago
        Yeah, from where I sit Chrome is the absolute first target, regardless of how many nails are being nailed into its coffin. There is some thought that if Apple opens up iOS a bit Chrome could make more headway there as well. Numbers I've heard are Chrome - 60%, Firefox < 5%.

dang 6y ago

The submitted title ("CNAME tracking's a disaster. uBlock Origin blocks it in FF. Chrome users are SOL") broke the site guidelines. Accounts that do that eventually lose submission privileges, so please don't do that. It looks like a fine submission otherwise! "Please use the original title, unless it is misleading or linkbait; don't editorialize." https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html

spenvo 6y ago
Thanks dang, sorry—I blanked out on that rule and will try to remember moving forward (I think I’ve made this mistake before). Cheers
- dang 6y ago
  Appreciated!

tinus_hn 6y ago

How can browsers defend against sites giving away their own private cookies to trackers? They could just as well send the data from the server side.

XzetaU8 6y ago

"Chrome users are currently completely susceptible to having private cookie data stolen on thousands of high-traffic sites" Not true, sure it's a workaround solution but with frogeye's block list [0] and uBO you're pretty much covered on Chrome regarding CNAME-tracking [0]:Geoffrey Frogeye's block list of first-party trackers https://hostfiles.frogeye.fr/ https://hostfiles.frogeye.fr/