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

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.