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fix: constrain AllowUniversalAccessFromFileURLs to file: origins in agent cluster key assignment#50789

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clavin/fix-coi-agent-cluster-key
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fix: constrain AllowUniversalAccessFromFileURLs to file: origins in agent cluster key assignment#50789
jkleinsc merged 3 commits into
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clavin/fix-coi-agent-cluster-key

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@clavin clavin commented Apr 7, 2026 •
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Description of Change

tl;dr: Adds a patch that fixes window.crossOriginIsolated for non-file: origins. I intend to upstream it.

HasPotentialUniversalAccessPrivilege() was treating the AllowUniversalAccessFromFileURLs setting as unconditional, returning true for all origins regardless of scheme. This caused non-file origins (http://, https://, and custom schemes) to lose their browser-provided AgentClusterKey when the setting was enabled, overriding it with a universal file agent key and routing them to universal_access_agent_ which carries no key.

Electron enables AllowUniversalAccessFromFileURLs in all renderers via the grant_file_protocol_extra_privileges fuse (on by default). After CL 7079680 moved cross-origin isolation status to the renderer's per-context agent cluster key, this caused self.crossOriginIsolated to return false even with COOP + COEP headers correctly set on non-file origins.

The fix splits the single has_potential_universal_access_privilege boolean in WindowAgentFactory::GetAgentForAgentClusterKey() into two separate parameters:

  • web_security_disabled: applies to all origins when web security is off (--disable-web-security, --run-web-tests).
  • allow_universal_access_from_file_urls: only takes effect for file: scheme origins (those with IsUniversalFileAgent() agent cluster keys), preserving their existing routing to universal_access_agent_.

This aligns the agent assignment logic with the origin privilege granting code in the same file (DocumentLoader::CalculateOrigin), which already correctly gates AllowUniversalAccessFromFileURLs behind origin->IsLocal().

This patch should be upstreamed, with updates to surrounding doc comments + tests.

Fixes #50242

Credit to @deepak1556 for identifying the regression source and suggesting the split approach in #50242

Verification

Tested with the gist repro from the issue. Also verified programmatically (red/green testing): a recent v43 nightly reports crossOriginIsolated: false, the patched build reports true.

Checklist

Release Notes

Notes: Fixed cross-origin isolation failing for non-file origins.

@clavin clavin added semver/patch backwards-compatible bug fixes target/41-x-y PR should also be added to the "41-x-y" branch. target/42-x-y PR should also be added to the "42-x-y" branch. labels Apr 7, 2026
@electron-cation electron-cation Bot added new-pr 🌱 PR opened recently and removed new-pr 🌱 PR opened recently labels Apr 7, 2026
@clavin clavin force-pushed the clavin/fix-coi-agent-cluster-key branch 2 times, most recently from c44f2d2 to 2f71022 Compare April 13, 2026 04:34
@clavin clavin marked this pull request as ready for review April 13, 2026 19:49
@clavin clavin requested a review from a team as a code owner April 13, 2026 19:49
@electron-cation electron-cation Bot added the new-pr 🌱 PR opened recently label Apr 13, 2026
deepak1556
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Thanks!

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deepak1556 commented Apr 13, 2026

Possible to add a regression test on our end based on the gist from the issue ?

@electron-cation electron-cation Bot removed the new-pr 🌱 PR opened recently label Apr 14, 2026
codebytere
codebytere reviewed Apr 15, 2026
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@clavin could you also link the CL so we know what upstream thinks before we merge this?

jkleinsc
jkleinsc previously requested changes Apr 16, 2026
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requesting changes until a test is added and an upstream CL is linked.

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clavin commented Apr 22, 2026

crbug filed: https://crbug.com/505299810

CL soon

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clavin commented Apr 27, 2026

CL: https://chromium-review.googlesource.com/c/chromium/src/+/7795303

next up: rebasing on main to resolve the merge conflict, linking to the CL in the patch description

@clavin clavin force-pushed the clavin/fix-coi-agent-cluster-key branch 2 times, most recently from b4cfe20 to d970d5b Compare April 28, 2026 19:52
@clavin clavin requested a review from jkleinsc April 29, 2026 14:46
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clavin commented Apr 29, 2026 •
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mergers: ready to land! edit: test added too!

clavin and others added 3 commits April 29, 2026 18:41
@clavin @claude
fix: constrain AllowUniversalAccessFromFileURLs to file: origins in a…
f235e4e 
…gent cluster key assignment

Fixes #50242

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
@clavin
sync patch with upstream CL
ce2f70a
@clavin
add test
c79bb99
@clavin clavin force-pushed the clavin/fix-coi-agent-cluster-key branch from d8198f5 to c79bb99 Compare April 29, 2026 22:42
@clavin clavin dismissed jkleinsc’s stale review April 29, 2026 22:43

added CL & test

@jkleinsc jkleinsc merged commit 212b53c into main Apr 30, 2026
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@jkleinsc jkleinsc deleted the clavin/fix-coi-agent-cluster-key branch April 30, 2026 13:36
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release-clerk Bot commented Apr 30, 2026

Release Notes Persisted

Fixed cross-origin isolation failing for non-file origins.

@trop trop Bot mentioned this pull request Apr 30, 2026
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trop Bot commented Apr 30, 2026

I have automatically backported this PR to "41-x-y", please check out #51403

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@trop trop Bot removed the target/41-x-y PR should also be added to the "41-x-y" branch. label Apr 30, 2026
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trop Bot commented Apr 30, 2026

I have automatically backported this PR to "42-x-y", please check out #51404

@trop trop Bot added in-flight/42-x-y and removed target/42-x-y PR should also be added to the "42-x-y" branch. labels Apr 30, 2026
jkleinsc added a commit that referenced this pull request May 1, 2026
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Revert "fix: constrain AllowUniversalAccessFromFileURLs to file: orig…
128a9f1 
…ins in agent cluster key assignment (#50789)"

This reverts commit b40ba2e.
@trop trop Bot added merged/42-x-y PR was merged to the "42-x-y" branch. merged/41-x-y PR was merged to the "41-x-y" branch. and removed in-flight/42-x-y in-flight/41-x-y labels May 1, 2026
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Setting relevant headers no longer makes the document cross-origin isolated

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