Astro Vercel Integration Exposes Critical Path Traversal Vulnerability (CVE-2026-33768)

A critical security flaw in the `@astrojs/vercel` integration allows unauthenticated attackers to rewrite internal server request paths, potentially leading to path traversal attacks. The vulnerability, tracked as CVE-2026-33768, stems from the serverless entrypoint reading the `x-astro-path` header and `x_astro_path` query parameter without any form of authentication or validation. This creates a direct vector for manipulating the internal routing logic of applications built with the Astro framework and deployed on Vercel.

The core of the issue lies in the `@astrojs/vercel` package versions prior to 10.0.2. The integration's handling of these specific headers and parameters is inherently insecure, as it trusts user-supplied input to dictate the internal request path. This design flaw bypasses standard security controls, making any Astro site deployed via this adapter vulnerable if it hasn't been patched. The GitHub security advisory (GHSA-mr6q-rp88-fx84) confirms the severity, prompting an urgent major version update from 9.0.5 to 10.0.2 to remediate the risk.

This vulnerability places thousands of production websites at immediate risk of unauthorized access to internal application routes and sensitive files. Developers and security teams must treat this as a high-priority patch, as the exploit requires no authentication and could be leveraged in automated attacks. The fix in version 10.0.2 involves removing or securing the insecure path rewriting mechanism. Failure to apply this update leaves applications exposed to a straightforward and potentially damaging server-side request forgery (SSRF) or path traversal attack surface.