Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765

# Authentication Bypass via Double URL Encoding in Astro ## Bypass for CVE-2025-64765 / GHSA-ggxq-hp9w-j794 --- ### 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' } } ); } ```

Source published

8 Dec 2025 16:26:43 UTC

Source modified

4 Feb 2026 02:27:12 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

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