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' }
}
);
}Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | astro | < 5.15.8 | 5.15.8 |
References
- https://github.com/withastro/astro/security/advisories/GHSA-ggxq-hp9w-j794
- https://github.com/withastro/astro/security/advisories/GHSA-whqg-ppgf-wp8c
- https://nvd.nist.gov/vuln/detail/CVE-2025-64765
- https://nvd.nist.gov/vuln/detail/CVE-2025-66202
- https://github.com/withastro/astro/commit/6f800813516b07bbe12c666a92937525fddb58ce
- https://github.com/withastro/astro
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N- Weakness (CWE)
CWE-647- Platform
- npm
- Package
astro- Disclosed
- 08.12.2025
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-whqg-ppgf-wp8c - CC BY 4.0
Vulnerability history: astro
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 27
- First → latest
- 10.2024 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 6
- Medium 15
- Low 5
Disclosures per year
- 2024: 3
- 2025: 11
- 2026: 13
-
Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765 this entry
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