Intent to Ship: Local Network Access restrictions for Background Fetch

[Chromestatus]

Contact emails

cth...@chromium.org

Explainer

No information provided

Specification

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

Summary

Background Fetch requests will now require that the service worker's origin has the necessary Local Network Access (LNA) permission in order to send requests to local or loopback servers. This aligns Chromium's implementation with the intent of the Background Fetch spec (that such requests go through the Fetch spec and have the same security policies applied to them, in this case Local Network Access checks). This prevents sites from bypassing LNA checks by using Background Fetch instead of regular Fetch. For enterprises, you can use existing Local Network Access enterprise policies in the same way you previously would have for regular Fetch API requests from service workers (see [LocalNetworkAccessRestrictionsTemporaryOptOut](https://chromeenterprise.google/policies/#LocalNetworkAccessRestrictionsTemporaryOptOut), [LocalNetworkAccessAllowedForUrls](https://chromeenterprise.google/policies/#LocalNetworkAccessAllowedForUrls), [LoopbackNetworkAllowedForUrls](https://chromeenterprise.google/policies/#LoopbackNetworkAllowedForUrls), [LocalNetworkAccessPermissionsPolicyDefaultEnabled](https://chromeenterprise.google/policies/#LocalNetworkAccessPermissionsPolicyDefaultEnabled), and [LocalNetworkAccessIpAddressSpaceOverrides](https://chromeenterprise.google/policies/#LocalNetworkAccessIpAddressSpaceOverrides)).

Blink component

Blink>BackgroundFetch

Web Feature ID

local-network-access

Motivation

This fixes a security issue where Background Fetch unintentionally bypasses security policies such as Local Network Access checks.

Initial public proposal

No information provided

TAG review

No information provided

TAG review status

Not applicable

Goals for experimentation

None

Risks

Interoperability and Compatibility

If the service worker's origin does not yet have the requisite Local Network Access permission, the background fetch request may fail. However, overall usage of Background Fetch is extremely low. We considered completely removing the ability for Background Fetch to make local network requests, which would be more disruptive. Treating Background Fetch requests the same as fetch() calls from a service worker context was deemed an appropriate middle ground.

Gecko: Shipped/Shipping (https://github.com/mozilla/standards-positions/issues/1260) Firefox is shipping LNA but does not support the BG Fetch API

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/520)

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?

LNA checks are not enforced in WebView.

Debuggability

No information provided

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

No
LNA is not enforced in WebView.

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

Yes

Flag name on about://flags

No information provided

Finch feature name

BackgroundFetchLocalNetworkAccess

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://crbug.com/455486148

Estimated milestones

Shipping on desktop	154
Shipping on Android	154

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/6225598451154944?gate=6680716673941504

This intent message was generated by Chrome Platform Status.

[Alex Russell]

LGTM1

[Mike Taylor]

LGTM2

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[Yoav Weiss (@Shopify)]

LGTM3

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