GHSA-x27w-589x-frm2: Astro: Unauthenticated path override in the @astrojs/vercel ISR function

When ISR is enabled, the serverless entrypoint lets an unauthenticated request decide which route the origin renders. The internal _isr function reads the x_astro_path query parameter and rewrites the request path to it without any authentication. Edge level access controls only ever see the /_isr path, so they do not apply to the route that actually gets rendered. This is the same confused deputy problem as CVE-2026-33768, reachable again through the ISR path.