[afilichev-SW]

Closes #36528

What I did

Bumped webpack-dev-middleware in @storybook/builder-webpack5 from ^6.1.2 to ^8.3.0 to pick up the fix for GHSA-g84c-rxfj-3j2c / CVE-2026-76844 (path traversal when publicPath has no trailing slash). There is no fix on the 6.x line.

No source changes were needed. The builder only uses the default export with publicPath, writeToDisk and stats, plus waitUntilValid() and close(). None of these changed between 6.x and 8.3. The breaking changes in 7.0 and 8.0 don't affect it:

• Node.js >= 20.9: Storybook already requires 20.19+ / 22.12+.
• webpack >= 5.101 (peer): the lockfile resolves 5.105.2, and every Angular version the Angular framework supports pins at least 5.102.1 (@angular-devkit/build-angular 21.0.0 pins 5.102.1).
• memfs 3 → 4: the builder doesn't touch outputFileSystem (it uses writeToDisk: true).
• getFilenameFromUrl became async: the builder doesn't use it.
• cacheImmutable is on by default: this only adds cache headers for content-hashed assets in dev.

The yarn.lock diff only contains the new middleware and its dependencies (memfs 4, @jsonjoy.com/*, range-parser, glob-to-regex.js). The old 6.x entry is removed.

I used Claude (Anthropic) to help investigate the change and prepare this PR. I reviewed the change; tests and sandbox checks were run with Claude's help.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

1. Run a webpack sandbox, e.g. yarn task --task dev --template react-webpack/18-ts --start-from auto.
2. Open Storybook and check that stories render and that editing a story hot-reloads it.
3. Check that a traversal request such as curl -i "http://localhost:6006/..%2fpackage.json" is rejected (403/404) and doesn't return the file.
4. Optionally, run yarn task --task build --template react-webpack/18-ts and check that the static build still works. The static build doesn't go through the middleware.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

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[coderabbitai]

Important

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Review was skipped as selected files did not have any reviewable changes.

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Walkthrough

The webpack builder package updates its declared webpack and webpack-dev-middleware dependency ranges.

Changes

Webpack builder dependency

Layer / File(s)	Summary
Update webpack dependency ranges code/builders/builder-webpack5/package.json	The package manifest changes webpack from 5 to ^5.101.0 and webpack-dev-middleware from ^6.1.2 to ^8.3.0.

Priority: ⬆️ High

Merge Risk: ⚪ Minimal · up to ca395

No incompatibility was established between the dependency update and the builder’s current middleware usage; no actionable merge-blocking risk remains.

Architecture Summary

Architecture risk: 🔵 Low · up to ca395

The change affects 1 system.

Changed systems: code

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — code (service) was modified; 1 changed file maps to changed impact.

Before / after behavior

• observed — Modified behavior in code/builders/builder-webpack5/package.json: The package dependency ranges change from webpack "5" and webpack-dev-middleware ^6.1.2 to webpack ^5.101.0 and webpack-dev-middleware ^8.3.0.

✨ Finishing Touches 💡 1

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Actionable comments posted: 1

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Inline comments:
Review comments at @code/builders/builder-webpack5/package.json:
- Around line 67-68: Update the webpack dependency range in the package manifest
to require webpack 5.101.0 or later, aligning it with the optional peer range
declared by webpack-dev-middleware 8.3.0.

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[afilichev-SW]

Thanks for fixing the dedupe, I missed running yarn dedupe --check locally.

[storybook-app-bot]

Package Benchmarks

^{Commit: 89a2fe4, ran on 7 October 2026 at 10:09:04 UTC}

The following packages have significant changes to their size or dependencies:

@storybook/builder-webpack5

	Before	After	Difference
Dependency count	181	205	🚨 +24 🚨
Self size	92 KB	92 KB	🎉 -41 B 🎉
Dependency size	38.84 MB	46.11 MB	🚨 +7.27 MB 🚨
Bundle Size Analyzer	Link	Link

@storybook/angular

	Before	After	Difference
Dependency count	186	213	🚨 +27 🚨
Self size	240 KB	240 KB	0 B
Dependency size	31.68 MB	39.40 MB	🚨 +7.72 MB 🚨
Bundle Size Analyzer	Link	Link

@storybook/ember

	Before	After	Difference
Dependency count	180	204	🚨 +24 🚨
Self size	13 KB	13 KB	🎉 -18 B 🎉
Dependency size	34.15 MB	41.42 MB	🚨 +7.27 MB 🚨
Bundle Size Analyzer	Link	Link

@storybook/nextjs

	Before	After	Difference
Dependency count	445	469	🚨 +24 🚨
Self size	641 KB	641 KB	0 B
Dependency size	62.56 MB	69.83 MB	🚨 +7.27 MB 🚨
Bundle Size Analyzer	Link	Link

@storybook/react-webpack5

	Before	After	Difference
Dependency count	265	289	🚨 +24 🚨
Self size	23 KB	23 KB	🎉 -12 B 🎉
Dependency size	51.29 MB	58.56 MB	🚨 +7.27 MB 🚨
Bundle Size Analyzer	Link	Link

@storybook/server-webpack5

	Before	After	Difference
Dependency count	193	217	🚨 +24 🚨
Self size	15 KB	15 KB	0 B
Dependency size	40.11 MB	47.38 MB	🚨 +7.27 MB 🚨
Bundle Size Analyzer	Link	Link

[afilichev-SW]

tests--linux was failing because of the memfs bump, 4.72.2 breaks the memfs-backed tests. I pinned memfs 4.x to 4.72.1 in yarn.lock in 171f566 to fix that (Happy to drop it if you'd rather update the tests for the newer memfs)