uBlock Origin users the use of new tracking techniques by advertising networks and web analytics systems for tracking movements and substituting ad blocks, which cannot be blocked by uBlock Origin and other ad-blocking extensions.
The essence of the method is that website owners wishing to place tracking or advertising code create a separate subdomain in DNS that points to the ad network or web analytics server (for example, a CNAME record f7ds.liberation.fr points to the tracking server liberation.eulerian.net). Thus, the ad code is formally loaded from the same primary domain as the website and therefore is not subject to blocking. The name for the subdomain is chosen in the form of a random identifier, which complicates blocking by mask, as the subdomain linked to the ad network is difficult to distinguish from subdomains that load other local page resources.
The developer of uBlock Origin to use the name in DNS to determine the associated host via CNAME. The method starting with
the experimental release for . To activate the check in the advanced settings, set the cnameAliasList value to ‘*’. In this case, all blacklist checks will also be duplicated for names resolved through CNAME. When updating, permissions must be granted to obtain information from DNS.
For Chrome, CNAME checking cannot be added, as the API is only available for extensions in Firefox and is not supported in Chrome. In terms of performance, determining CNAME should not introduce additional overhead, apart from the processor resources spent on reapplying rules for another name, as the browser has already performed the resolution and the value should be cached. The protection method can be circumvented by directly binding the name to an IP without using CNAME, but this approach complicates maintenance (if the ad network’s IP address changes, it will be necessary to change the data on all DNS servers of the publishers) and can be bypassed by creating a blacklist of tracker IP addresses.
Source: opennet.ru
