CVE-2025-66202
📋 TL;DR
This vulnerability allows unauthenticated attackers to bypass path-based authentication checks in Astro web framework middleware by using double-encoded URLs. Attackers can access protected routes that should require authentication. All Astro applications using middleware for authentication on versions 5.15.7 and below are affected.
💻 Affected Systems
- Astro web framework
📦 What is this software?
Astro by Astro
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of protected application routes, potentially exposing sensitive data or administrative functionality to unauthorized users.
Likely Case
Unauthorized access to protected application areas, potentially exposing user data or internal functionality.
If Mitigated
Limited impact if additional authentication layers exist beyond path-based middleware checks.
🎯 Exploit Status
Exploitation requires crafting double-encoded URLs but is straightforward for attackers with basic web knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.15.8
Vendor Advisory: https://github.com/withastro/astro/security/advisories/GHSA-ggxq-hp9w-j794
Restart Required: Yes
Instructions:
Update Astro package to version 5.15.8 or later using npm: npm update astro@^5.15.8
Rebuild and redeploy your Astro application
Test protected routes to ensure authentication bypass is no longer possible
🔧 Temporary Workarounds
Middleware URL normalization
allImplement custom middleware that properly normalizes and decodes URLs before authentication checks
// Example middleware code to decode URLs multiple times
const normalizedPath = decodeURIComponent(decodeURIComponent(req.url))
🧯 If You Can't Patch
- Implement additional authentication layers beyond path-based middleware checks
- Use web application firewall (WAF) rules to block double-encoded URL patterns
🔍 How to Verify
Check if Vulnerable:
Check package.json for Astro version <=5.15.7 and verify if middleware is used for path-based authenticationCheck Version:
npm list astro | grep astroVerify Fix Applied:
Test protected routes with double-encoded URLs after updating to verify authentication bypass is prevented📡 Detection & Monitoring
Log Indicators:
- Multiple URL decoding attempts in single requests
- Access to protected routes from unauthenticated sources
- Unusual URL patterns with multiple percent encodings
Network Indicators:
- HTTP requests with double-encoded URL paths
- Access patterns bypassing expected authentication flows
SIEM Query:
web.url contains "%25" AND (web.status_code = 200 OR web.status_code = 302) AND NOT auth.user exists