What’s Vulnerable › Vulnerabilities

CVE-2025-66202: Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-09 · updated 2026-10-07
• Weakness: CWE-647

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.

Affected products

• withastro astro: before 5.15.8 — fixed in 5.15.8

How to fix

Upgrade to a fixed version: withastro astro 5.15.8. Check the vendor advisory for mitigations.

References

• 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

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