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

> Unauthenticated attackers can bypass middleware authentication checks using double URL encoding to access protected routes in Astro applications.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Dec 2025
- **Updated:** 9 Dec 2025
- **Also known as:** GHSA-whqg-ppgf-wp8c

## What is CVE-2025-66202?

CVE-2025-66202 is a medium-severity authentication bypass vulnerability in withastro astro, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-647 (Use of Non-Canonical URL Paths for Authorization Decisions)

## Which versions are affected by CVE-2025-66202?

2 open source packages ship an affected version, including astro. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `astro` | npm | All versions | 5.15.8 |
| `astro` | npm | All versions | 5.15.8 |

Products: Astro Astro.

## How do I fix CVE-2025-66202?

Upgrade astro to 5.15.8 or later.

## Is CVE-2025-66202 being exploited?

There is no known exploitation of CVE-2025-66202 in the wild and no public exploit code.

## Other vulnerabilities in withastro astro

- [CVE-2024-56159](https://insights.sbomify.com/CVE-2024-56159/): Server source code is exposed to the public if sourcemaps are enabled (high 7.8)
- [CVE-2026-54299](https://insights.sbomify.com/CVE-2026-54299/): Astro: Host header SSRF in prerendered error page fetch (high 7.5)
- [CVE-2025-59837](https://insights.sbomify.com/CVE-2025-59837/): astro allows bypass of image proxy domain validation leading to SSRF and potential XSS (high 7.2)
- [CVE-2026-50146](https://insights.sbomify.com/CVE-2026-50146/): Astro: Reflected XSS via unescaped slot name (high 7.1)
- [CVE-2025-64764](https://insights.sbomify.com/CVE-2025-64764/): Astro is vulnerable to Reflected XSS via the server islands feature (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-66202 and fix it if it is affected.

What it is: CVE-2025-66202 is a medium-severity authentication bypass vulnerability in withastro astro, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-66202 in the wild and no public exploit code.

Affected packages and fixed versions:
- astro (npm): affected all versions; fixed in 5.15.8
- astro (npm): affected all versions; fixed in 5.15.8

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-66202/ (Markdown: https://insights.sbomify.com/CVE-2025-66202/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-66202
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66202
- OSV: https://osv.dev/vulnerability/CVE-2025-66202

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-66202/
Summaries are generated and may contain mistakes; the official description above is the record.