CNAME cloaking is a tracking evasion scheme that is not new but is rapidly gaining in popularity. Mozilla released Firefox 86 on Tuesday, with it yet another new anti-tracking feature build into the browser’s Enhanced Tracking Protection (ETP) Total Cookie Protection. Google laid out a roadmap for making third party cookies obsolete by 2022. Google is working on creating alternative technologies/standards that will permit ad personalization without affecting user privacy. Researchers say the technique leads to session fixation and persistent cross-site scripting vulnerabilities.
Source: https://www.helpnetsecurity.com/2021/02/24/browsers-anti-tracking/