Intent to Ship: CORS enforcement for Background Fetch

[Chromestatus]

Contact emails

cth...@chromium.org

Explainer

No information provided

Specification

https://wicg.github.io/background-fetch

Summary

Starting in Chrome 157, 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/).

Blink component

Blink>BackgroundFetch

Web Feature ID

background-fetch

Motivation

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.)

Initial public proposal

No information provided

TAG review

No information provided

TAG review status

Not applicable

Goals for experimentation

None

Risks

Interoperability and Compatibility

Overall usage of Background Fetch is extremely low. We considered completely deprecating and removing Background Fetch, which would be more disruptive. Treating Background Fetch requests the same as fetch() calls and requiring the same security policy enforcement (and server opt-ins via things like Access-Control-Allow-Origins) may cause some temporary breakage as sites and servers adjust (if they don't already have the necessary configuration for regular fetch requests).

Gecko: No signal

WebKit: No signal

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Debuggability

No information provided

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

Yes

Is this feature fully tested by web-platform-tests?

Yes

Flag name on about://flags

No information provided

Finch feature name

BackgroundFetchCorsEnforcement

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Estimated milestones

Shipping on desktop	157
Shipping on Android	157

Anticipated spec changes

Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).

None. This brings Chromium's implementation into alignment with the intent of the Background Fetch spec (which delegates security policy enforcement to the Fetch spec).

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6210300985606144?gate=6167177091743744

This intent message was generated by Chrome Platform Status.

[Chris Harrelson]

LGTM1

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[Alex Russell]

LGTM2. Thanks for getting us closer to the spec.

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[Mike Taylor]

LGTM3

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