CVE-2025-66202
Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765
Impact
# 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' } } ); } ```
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | astro | < 5.15.8 | 5.15.8 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Astro | Astro | before 5.15.8 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/withastro/astro/commit/6f800813516b07bbe12c666a92937525fddb58ce
- https://github.com/withastro/astro/security/advisories/GHSA-ggxq-hp9w-j794
- https://github.com/withastro/astro/security/advisories/GHSA-whqg-ppgf-wp8c
- https://github.com/advisories/GHSA-whqg-ppgf-wp8c
- https://nvd.nist.gov/vuln/detail/CVE-2025-64765
- https://nvd.nist.gov/vuln/detail/CVE-2025-66202