EUVD-2026-262950

fkie_cve-2025-66202

Astro is a web framework. Versions 5.15.7 and below have a double URL encoding bypass which allows any unauthenticated attacker to bypass path-based authentication checks in Astro middleware, granting unauthorized access to protected routes. While the original CVE-2025-64765 was fixed in v5.15.8, the fix is insufficient as it only decodes once. By using double-encoded URLs, attackers can still bypass authentication and access any route protected by middleware pathname checks. This issue is fixed in version 5.15.8.

GHSA-whqg-ppgf-wp8c — Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765

Affected: npm: astro

# Authentication Bypass via Double URL Encoding in Astro ## Bypass for CVE-2025-64765 / GHSA-ggxq-hp9w-j794

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### Summary

A **double URL encoding bypass** allows any unauthenticated attacker to bypass path-based authentication checks in Astro middleware, granting unauthorized access to protected routes. While the original CVE-2025-64765 (single URL encoding) was fixed in v5.15.8, the fix is insufficient as it only decodes once. By using double-encoded URLs like `/%2561dmin` instead of `/%61dmin`, attackers can still bypass authentication and access protected resources such as `/admin`, `/api/internal`, or any route protected by middleware pathname checks.

## Fix

A more secure fix is just decoding once, then if the request has a %xx format, return a 400 error by using something like :

``` if (containsEncodedCharacters(pathname)) { // Multi-level encoding detected - reject request return new Response( 'Bad Request: Multi-level URL encoding is not allowed', { status: 400, headers: { 'Content-Type': 'text/plain' } } ); } ```

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EUVD-2026-262950

fkie_cve-2025-66202

GHSA-whqg-ppgf-wp8c — Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765