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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2025-66202: 0.31% estimated exploitation activity in the next 30 days; percentile 24.35 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 :

Published by the source

8 Dec 2025, 16:26 UTC

Last modified by the source

4 Feb 2026, 02:27 UTC

Source last checked

26 Oct 2026, 12:41 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-whqg-ppgf-wp8c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-whqg-ppgf-wp8c

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# Patch Next advisory brief: CVE-2025-66202

Advisory: Astro has an Authentication Bypass via Double URL Encoding, a bypass for CVE-2025-64765
IDs: CVE-2025-66202, GHSA-whqg-ppgf-wp8c
Record: https://patchnext.com/advisories/cve-2025-66202 (revision 2, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: astro 5.15.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm astro: affected < 5.15.8; fixed in 5.15.8

## Suggested inspection (read-only)
- `npm ls astro --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on astro.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-whqg-ppgf-wp8c (OSV record GHSA-whqg-ppgf-wp8c lists affected ranges: npm astro >=0 <5.15.8 (fixed))
- Verified: https://github.com/advisories/GHSA-whqg-ppgf-wp8c (GitHub-reviewed advisory GHSA-whqg-ppgf-wp8c lists affected ranges: npm astro >=0 <5.15.8)

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