Starting in Chrome 154, the Background Fetch API now enforces Cross-Origin Resource Sharing (CORS). This update aligns Chromium's implementation with the intent of the [Background Fetch spec](https://wicg.github.io/background-fetch/). This ensures that Background Fetch requests are subject to the same security policies, such as Local Network Access checks. This update prevents sites from bypassing CORS (and other security policy checks) by using Background Fetch instead of regular [Fetch](https://fetch.spec.whatwg.org/).
This fixes a security issue where Background Fetch unintentionally bypasses security policies such as CORS (and CORP/COEP/DIP). (crbug.com/515243254 is our meta bug tracking all of the different web platform security issues with Background Fetch.)