CVE-2025-66202 Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765
Unauthenticated attackers can bypass middleware authentication checks using double URL encoding to access protected routes in Astro applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-66202?
CVE-2025-66202 is a medium-severity authentication bypass vulnerability in withastro astro, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-647
Which versions are affected by CVE-2025-66202?
2 open source packages ship an affected version, including astro. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
astro npm | All versions | 5.15.8 |
astro npm | All versions | 5.15.8 |
Products include Astro Astro.
How do I fix CVE-2025-66202?
Upgrade astro to 5.15.8 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2025-66202 being exploited?
There is no known exploitation of CVE-2025-66202 in the wild and no public exploit code.
Other vulnerabilities in withastro astro
- CVE-2024-56159 Server source code is exposed to the public if sourcemaps are enabled
- CVE-2026-54299 Astro: Host header SSRF in prerendered error page fetch
- CVE-2025-59837 astro allows bypass of image proxy domain validation leading to SSRF and potential XSS
- CVE-2026-50146 Astro: Reflected XSS via unescaped slot name
- CVE-2025-64764 Astro is vulnerable to Reflected XSS via the server islands feature
Sources
Also known as GHSA-whqg-ppgf-wp8c.