Executive brief
A security vulnerability exists in the Astro framework's Vercel adapter when Incremental Static Regeneration (ISR) is enabled. This flaw allows an unauthorized person to bypass security rules—such as firewalls or login requirements—that are configured at the network edge. By sending a specially crafted web request, an attacker can view sensitive pages (like admin dashboards) that should otherwise be protected, potentially leading to the exposure of private data.
Technical details
The vulnerability is a 'confused deputy' issue (CWE-441) within the `@astrojs/vercel` serverless entrypoint. When ISR is enabled, the internal `_isr` function processes the `x_astro_path` query parameter to rewrite the request path without verifying a middleware secret. Because the `_isr` route is publicly addressable and the required `x-vercel-isr` header is automatically set by Vercel (even for external requests), an unauthenticated attacker can force the origin to render any GET-accessible route. This bypasses edge-level security measures like Vercel firewall rules and edge middleware, as these components only see the initial `/_isr` path. The issue was a regression introduced in version 10.0.3 and is fixed in version 11.0.3.
Affected products
- Astro @astrojs/vercel >= 10.0.3, < 11.0.3
Timeline
- 2026-07-17: disclosed
- 2026-07-20: advisory
- 2026-07-20: patched: Fixed in @astrojs/vercel 11.0.3