{
  "canonical_id": "astro--CVE-2025-66202",
  "system_id": "astro",
  "display_name": "Astro",
  "category": "frameworks",
  "advisory_mode": "core",
  "title": "Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765",
  "summary": "# 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                'Bad Request: Multi-level URL encoding is not allowed',\n                {\n                    status: 400,\n                    headers: { 'Content-Type': 'text/plain' }\n                }\n            );\n        }\n```",
  "published_at": "2025-12-08T16:26:43Z",
  "updated_at": "2026-02-04T02:27:12.689316Z",
  "severity": "low",
  "cvss_score": 3.1,
  "exploit_status": "unknown",
  "source_confidence": "official",
  "official_source_url": "https://github.com/withastro/astro/security/advisories/GHSA-ggxq-hp9w-j794",
  "secondary_source_urls": [
    "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"
  ],
  "aliases": [
    "CVE-2025-66202",
    "GHSA-whqg-ppgf-wp8c"
  ],
  "cve_ids": [
    "CVE-2025-66202"
  ],
  "ghsa_ids": [
    "GHSA-whqg-ppgf-wp8c"
  ],
  "osv_ids": [
    "GHSA-whqg-ppgf-wp8c"
  ],
  "affected_versions": [
    "introduced=0, fixed<5.15.8"
  ],
  "fixed_versions": [
    "5.15.8"
  ],
  "package_name": "astro",
  "render_markdown": true,
  "case_path": "07-framework-security/frameworks/astro/cases/astro-cve-2025-66202.md",
  "secure_code_topics": [
    "authz-server-side-recheck",
    "csp-trusted-types",
    "proxy-trust-boundary"
  ],
  "status": "generated",
  "triage_reasons": [],
  "verification_status": "triage-manual",
  "verification_mode": "synthetic",
  "last_verified_at": null,
  "last_run_id": null,
  "evidence_bundle": null,
  "historical_status": null,
  "latest_status": null,
  "browser_evidence": {
    "required": false,
    "present": false,
    "refs": []
  },
  "repro_profile_id": "proxy-boundary-generic",
  "artifact_mode": "synthetic",
  "blocked_reason": null,
  "metadata": {
    "source_names": [
      "OSV Astro"
    ],
    "source_kinds": [
      "osv-batch"
    ],
    "candidate_count": 1
  }
}