https://arstechnica.com/information-technology/2022/01/safari-and-ios-bug-reveals-your-browsing-activity-and-id-in-real-time/

For the past four months, Apple’s iOS and iPadOS devices and Safari browser have violated one of the Internet’s most sacrosanct security policies. The violation results from a bug that leaks user identities and browsing activity in real time.

The same-origin policy is a foundational security mechanism that forbids documents, scripts, or other content loaded from one origin—meaning the protocol, domain name, and port of a given webpage or app—from interacting with resources from other origins. Without this policy, malicious sites—say, badguy.example.com—could access login credentials for Google or another trusted site when it’s open in a different browser window or tab.