CVE-2026-73423 — astro

Summary

In the composable astro/hono pipeline, the security.checkOrigin protection is only installed by the middleware() primitive. The actions() and pages() primitives each dispatch to user code independently, so a pipeline that mounts either primitive before (or without) middleware() will bypass the origin check for those requests.

Details

security.checkOrigin (default: true) is intended to reject cross-site POST/PUT/PATCH/DELETE form submissions. In the classic pipeline (astro() all-in-one), the check always runs because Astro injects a virtual middleware module even when the user has no src/middleware.ts. In the composable astro/hono pipeline, the user assembles primitives manually. The check is only installed inside middleware() — so:

• Mounting actions() before middleware() allows cross-origin form-encoded action requests to execute before the gate runs. The examples/advanced-routing example and the Cloudflare hono docs shipped this order.
• Omitting middleware() entirely (reasonable for apps with no custom middleware) silently drops checkOrigin protection for all on-demand endpoints and pages dispatched through pages().

The attack is a blind write-only CSRF: the attacker can trigger a state-mutating action or endpoint handler using the victim's cookies, but cannot read the cross-origin response body.

Affected versions

Astro >= 7.0.0 when using the composable astro/hono pipeline with either:

• actions() mounted before middleware(), or
• pages() used without middleware()

The default (non-composable) pipeline is not affected.

Fix

The origin check is now applied at each dispatch sink (ActionHandler.handle and PagesHandler.handleWithErrorFallback), gated on manifest.checkOrigin, using the same predicate as the middleware. The check is order-independent and a no-op when middleware() has already run.

Fix: https://github.com/withastro/astro/pull/17250

Workaround

Ensure middleware() is mounted before both actions() and pages() in the composable pipeline, and that it is always included even when no custom middleware logic is needed:

app.use(middleware());
app.use(actions());
app.use(pages());