iCloud Private Relay aims to improve anonymity on the web by employing a dual-hop architecture that effectively shields users’ IP address, location, and DNS requests from websites and network service providers. It achieves this by routing users’ internet traffic on the Safari browser through two proxies in order to mask who’s browsing and where that data is coming from. The vulnerability arose from a specific candidate dubbed “Server Reflexive Candidate” that’s generated by a server when data from the endpoint needs to be transmitted around a NAT (Network Address Translator)”]
Source: https://thehackernews.com/2021/09/apples-new-icloud-private-relay-service.html