astro@6.4.7

withastro/astroastro@6.4.7Jun 15, 2026by astrobot-houston

AI Summary

This is a patch release for the Astro framework that addresses various bugs related to localization URL handling, SSR performance in hybrid mode, MDX custom elements, and CSS Hot Module Replacement (HMR). It also introduces a JSON schema for Cloudflare configuration.

Key Highlights

Fixes locale URL functions (getRelativeLocaleUrl, etc.) to strip trailing slashes when configured to 'never'
Fixes double URL-encoded paths to support valid double-encoded URLs (like Sanity Studio) while maintaining security against CVE-2025-66202
Fixes prerendered redirects causing massive bundle size inflation in hybrid mode
Fixes HMR not triggering for files inside the `src/middleware/` directory
Adds a JSON schema to the Wrangler configuration file generated by `astro add cloudflare`

New Features

JSON schema support in Wrangler configuration
Improved diagnostics for incorrect .astro file parsing

Full Release Notes

### Patch Changes

-   [#17035](https://github.com/withastro/astro/pull/17035) [`197e50e`](https://github.com/withastro/astro/commit/197e50e2e37168a9b9e8a014c13d1308b2220ca1) Thanks [@astrobot-houston](https://github.com/astrobot-houston)! - Fixes `getRelativeLocaleUrl`, `getAbsoluteLocaleUrl`, and `getAbsoluteLocaleUrlList` to strip trailing slashes when `trailingSlash: 'never'` is configured

-   [#16967](https://github.com/withastro/astro/pull/16967) [`3719765`](https://github.com/withastro/astro/commit/37197652630ffbc11efaaec1865869410b8dfd70) Thanks [@astrobot-houston](https://github.com/astrobot-houston)! - Fixes double URL-encoded paths returning 400 Bad Request on on-demand routes

    Previously, any URL containing a double-encoded character (like `%255B`, which is `[` encoded twice) was unconditionally rejected with a `400 Bad Request` before middleware or route handlers could run. This broke embedded tools like Sanity Studio whose client-side router legitimately produces double-encoded URLs.

    The fix replaces the rejection approach with iterative decoding — multi-level percent-encoding is now fully resolved to its canonical form before being passed to middleware and route matching. This preserves the security fix for CVE-2025-66202 (middleware authorization bypass via double encoding) because middleware now always sees the fully decoded path, making bypass impossible. For example, `/api/%2561dmin` is decoded to `/api/admin`, which middleware can correctly block.

-   [#17066](https://github.com/withastro/astro/pull/17066) [`2f4d92a`](https://github.com/withastro/astro/commit/2f4d92a72b00354114359b5746d573fbfd3b334f) Thanks [@matthewp](https://github.com/matthewp)! - Fixes prerendered redirect targets being incorrectly bundled into the SSR function in hybrid mode, causing massive bundle size inflation

-   [#16882](https://github.com/withastro/astro/pull/16882) [`621beb7`](https://github.com/withastro/astro/commit/621beb70fe957ecc73c3407c240392507613e0fd) Thanks [@jettwayio](https://github.com/jettwayio)! - fix(render): honour compressHTML when joining head elements

-   [#16892](https://github.com/withastro/astro/pull/16892) [`8d753b0`](https://github.com/withastro/astro/commit/8d753b0b671971b78e7064fe38c2b0b518823627) Thanks [@astrobot-houston](https://github.com/astrobot-houston)! - Fixes custom elements in MDX having their children's `slot` attribute stripped by the JSX runtime

    When custom elements (tags with hyphens like `<my-element>`) are used in MDX files, the `slot` HTML attribute on their children is now correctly preserved. Previously, the shared JSX runtime would treat `slot` as an Astro slot assignment and remove it from the output, breaking Shadow DOM named slot distribution for web components.

-   [#16957](https://github.com/withastro/astro/pull/16957) [`544ee76`](https://github.com/withastro/astro/commit/544ee763d7f7894e3b588daa14b09ef32a4d794a) Thanks [@thelazylamaGit](https://github.com/thelazylamaGit)! - Fixes stale inline CSS in server-rendered HTML after CSS file edits during dev

    When editing a CSS file (`.css`, `.scss`, etc.) during development, the inline `<style>` tags in server-rendered HTML would retain old CSS content instead of updating. This caused a brief flash of old CSS (FOUC) on fresh page loads before Vite's client-side HMR corrected the styles.

    The fix ensures that Astro's per-route dev CSS virtual modules are invalidated in both the SSR module graph and the module runner's evaluation cache when a style file changes, so the next page render picks up the fresh CSS.

-   [#17044](https://github.com/withastro/astro/pull/17044) [`2220d22`](https://github.com/withastro/astro/commit/2220d22f8c7278988560d0e4b4f378c9967e9bae) Thanks [@astrobot-houston](https://github.com/astrobot-houston)! - Fixes CSS from `client:only` islands leaking to unrelated pages when Rollup bundles non-CSS-importing modules into the same chunk as CSS-importing modules

-   [#17040](https://github.com/withastro/astro/pull/17040) [`7c4763d`](https://github.com/withastro/astro/commit/7c4763d31b94ccbdc2339992d73e087912e5b8e3) Thanks [@astrobot-houston](https://github.com/astrobot-houston)! - Fixes HMR not triggering for files inside the `src/middleware/` directory during dev

-   [#16672](https://github.com/withastro/astro/pull/16672) [`52fc862`](https://github.com/withastro/astro/commit/52fc86213e6412b6f9f3b70a2616d52b5fb783a9) Thanks [@martinheidegger](https://github.com/martinheidegger)! - Fixes support for numeric IDs in YAML frontmatter when using content collection references

-   [#16762](https://github.com/withastro/astro/pull/16762) [`9de80ae`](https://github.com/withastro/astro/commit/9de80ae486bc43c8680fda099a125d836e78b552) Thanks [@alexanderdombroski](https://github.com/alexanderdombroski)! - Adds a JSON schema to the Wrangler configuration file generated when running `astro add cloudflare`

-   [#17046](https://github.com/withastro/astro/pull/17046) [`ef771ec`](https://github.com/withastro/astro/commit/ef771ece349eedb6e0b3b240b020fb96df208a92) Thanks [@ematipico](https://github.com/ematipico)! - Improves the diagnostics emitted when Astro parses incorrect `.astro` files.