GHSA-WHQG-PPGF-WP8C

Vulnerability from github – Published: 2025-12-08 16:26 – Updated: 2025-12-09 16:28
VLAI?
Summary
Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765
Details

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' }
                }
            );
        }
Severity ?
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "astro"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.15.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-66202"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-647"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-12-08T16:26:43Z",
    "nvd_published_at": "2025-12-09T00:15:48Z",
    "severity": "MODERATE"
  },
  "details": "# Authentication Bypass via Double URL Encoding in Astro\n## Bypass for CVE-2025-64765 / GHSA-ggxq-hp9w-j794\n\n---\n\n### Summary\n\nA **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.\n\n\n## Fix \n\nA more secure fix is just decoding once, then if the request has a %xx format, return a 400 error by using something like :\n\n```\nif (containsEncodedCharacters(pathname)) {\n            // Multi-level encoding detected - reject request\n            return new Response(\n                \u0027Bad Request: Multi-level URL encoding is not allowed\u0027,\n                {\n                    status: 400,\n                    headers: { \u0027Content-Type\u0027: \u0027text/plain\u0027 }\n                }\n            );\n        }\n```",
  "id": "GHSA-whqg-ppgf-wp8c",
  "modified": "2025-12-09T16:28:41Z",
  "published": "2025-12-08T16:26:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/security/advisories/GHSA-ggxq-hp9w-j794"
    },
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/security/advisories/GHSA-whqg-ppgf-wp8c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-64765"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-66202"
    },
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/commit/6f800813516b07bbe12c666a92937525fddb58ce"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/withastro/astro"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765"
}


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