Intent to Experiment: Local Network Access
Hubert Chao
Note: this is for pre-stable experimentation through Finch, not for an Origin Trial.
Contact emails
Explainer
https://github.com/WICG/local-network-access
Specification
https://docs.google.com/document/d/1n0kKxt9pS9qDlu_9i5W8IXA594r4pUOKmN9H35cZ8j0/edit?tab=t.0
Design docs
https://github.com/explainers-by-googlers/local-network-access
https://docs.google.com/document/d/1n0kKxt9pS9qDlu_9i5W8IXA594r4pUOKmN9H35cZ8j0/edit?usp=sharing
Summary
Restricts the ability to make requests to the user's local network, gated behind a permission prompt.
A local network request is any request from a public website to a local IP address or loopback, or from a local website (e.g. intranet) to loopback. Gating the ability for websites to perform these requests behind a permission mitigates the risk of cross-site request forgery attacks against local network devices such as routers, and reduces the ability of sites to use these requests to fingerprint the user's local network.
This permission is restricted to secure contexts. If granted, the permissions additionally relaxes mixed content blocking for local network requests (since many local devices are not able to obtain publicly trusted TLS certificates for various reasons).
This work supersedes a prior effort called "Private Network Access" (e.g., https://chromestatus.com/feature/5737414355058688, https://chromestatus.com/feature/5954091755241472) which used preflight requests to have local devices opt-in.
Blink component
Blink>SecurityFeature>CORS>PrivateNetworkAccess
TAG review
https://github.com/w3ctag/design-reviews/issues/1116
TAG review status
Pending
Origin Trial documentation link
https://github.com/WICG/local-network-access
Risks
Interoperability and Compatibility
Interoperability risks:
LNA requires a Secure Context to make local network requests, but exempts some of these local network requests from mixed content checks (if the user grants permission). If another browser does not implement LNA, these same local network requests might be blocked as mixed content, or the site might need to serve over HTTPS for Chrome and over HTTP for browsers that don't implement LNA (to avoid triggering mixed content).
Compatibility risks:
There are some local network requests types that we cannot know ahead of time will be going to the local network (e.g., a subresource request to http://test.example which then resolves to 192.168.0.1). These would be blocked as mixed content, as mixed content checks happen before hostname resolution (i.e., they occur before "Obtain a connection" in Fetch). Explicit local IP addresses, `.local` domains, and fetch() requests with the new `targetAddressSpace` fetch() option are exempted from mixed content checks, but other connection types may be difficult for developers (e.g., WebSockets https://github.com/explainers-by-googlers/local-network-access/issues/16).
We hope that our Dev Trial will help identify compatibility issues. When we fully ship we also plan on running a reverse origin trial to allow sites to (temporarily) opt-out of the secure contexts requirement -- this would be an escape hatch for mixed content.
Gecko: Under consideration (https://groups.google.com/a/mozilla.org/g/dev-platform/c/B8oN3ARp_j0/m/rWKXmnj4AAAJ) Firefox is prototyping based on our spec draft, no formal request for signals yet
WebKit: No signal No request for signals yet
Web developers: Mixed signals (https://github.com/explainers-by-googlers/local-network-access/issues) Feedback from developers has been mixed, both due the new burden of a permission prompt (compared to PNA) and from some of the difficulty of navigating mixed content (the same as PNA). Many developers understand the reasoning behind adding the new permission though, and are productively engaging on how they can avoid issues.
Other signals: Brave ships a "localhost access" permission (see https://brave.com/privacy-updates/27-localhost-permission/)
Ergonomics
N/A
Activation
A new permission will be shown to users, which may be unexpected, and if users deny the permission functionality may break (potentially requiring additional support from site owners). Part of our goal for having a Dev Trial is to give site owners time to adjust their requests (especially if they need to use the mixed content exemptions) and to potentially adapt their UX flows so the permission requests are less surprising to users.
Security
Exempting some requests from mixed content checks based on declared targetAddressSpace could potentially be used to arbitrarily bypass mixed content. To avoid this, LNA does an additional check that the actual resolved address space matches what was declared, and blocks the request if it does not.
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?
None
Goals for experimentation
We intend to evaluate implementation of Local Network Access (LNA) through more widespread testing to ensure that we (a) do not capture any requests that are not LNA requests, and (b) all request that are LNA are captured and trigger a permissions check.
Intending to turn on up to 100% in Chrome Canary/Dev/Beta channel via Finch.
Experiment Risks
There may be false positives (request that are captured as LNA requests that are not) and false negatives (request that are LNA request that are not captured).
There is additional breakage risk with LNA request from non-secure contexts, as well as mixed-content LNA requests.
Ongoing technical constraints
None
Debuggability
When a request would be blocked under LNA, we add a new DevTools Issue with details.
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?
No
Android WebView currently doesn't support letting apps grant any new permission types, so the Local Network Access permission is currently unconditionally granted in WebView. Android is separately adding a Local Network permission which would apply to the app that embeds a WebView https://developer.android.com/privacy-and-security/local-network-permission
Is this feature fully tested by web-platform-tests?
No
We have started working on building out a test suite but it is still a work-in-progress. https://wpt.fyi/results/fetch/local-network-access
DevTrial instructions
https://developer.chrome.com/blog/local-network-access
Flag name on about://flags
local-network-access-check
Finch feature name
LocalNetworkAccessChecks
Requires code in //chrome?
True
Tracking bug
Estimated milestones
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5152728072060928
Links to previous Intent discussions
Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CALMy46SB%2Bv9dnp-wrJ4WH0R4UJmWuutq1st92%3D_zOyhnLJ_vkw%40mail.gmail.com
Ready For Developer Testing:
https://groups.google.com/a/chromium.org/g/blink-dev/c/D4nqAa3FUN8/m/WFVmJYh0BAAJ
Rick Byers
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Erik Anderson
Double checking: you will have the reverse OT infrastructure set up before proceeding to a stable channel experiment, correct?
Rick Byers
Hubert Chao
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