CVE-2025-66415
📋 TL;DR
CVE-2025-66415 is an authorization bypass vulnerability in fastify-reply-from, a Fastify plugin for HTTP request forwarding. Attackers can craft malicious URLs to access routes that should be restricted, even when reply.from is configured for specific routes only. This affects all applications using vulnerable versions of fastify-reply-from.
💻 Affected Systems
- fastify-reply-from
📦 What is this software?
Reply From by Fastify
⚠️ Risk & Real-World Impact
Worst Case
Complete bypass of route-based access controls, allowing attackers to access internal APIs, administrative endpoints, or sensitive data that should be restricted.
Likely Case
Unauthorized access to specific backend services or APIs that should be protected by route filtering, potentially exposing sensitive information.
If Mitigated
Limited impact if proper network segmentation and additional authentication layers exist, though route filtering would still be bypassed.
🎯 Exploit Status
Exploitation requires crafting specific URLs but does not require authentication to the vulnerable application.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 12.5.0
Vendor Advisory: https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-2q7r-29rg-6m5h
Restart Required: Yes
Instructions:
1. Update package.json to specify fastify-reply-from version 12.5.0 or higher. 2. Run npm update fastify-reply-from or yarn upgrade fastify-reply-from. 3. Restart your Fastify application.
🔧 Temporary Workarounds
Route validation middleware
allImplement custom middleware to validate and sanitize URLs before they reach fastify-reply-from
Network filtering
allUse WAF or reverse proxy rules to block suspicious URL patterns targeting the forwarding endpoint
🧯 If You Can't Patch
- Implement strict input validation for all URLs processed by fastify-reply-from
- Add additional authentication/authorization checks before forwarding requests
🔍 How to Verify
Check if Vulnerable:
Check package.json or package-lock.json for fastify-reply-from version. If version is below 12.5.0, the system is vulnerable.Check Version:
npm list fastify-reply-from | grep fastify-reply-fromVerify Fix Applied:
After updating, verify the installed version is 12.5.0 or higher using npm list fastify-reply-from or checking package-lock.json.📡 Detection & Monitoring
Log Indicators:
- Unusual URL patterns in requests to forwarding endpoints
- Access to routes that should be filtered by fastify-reply-from configuration
Network Indicators:
- HTTP requests with crafted URLs containing path traversal or parameter manipulation
SIEM Query:
source="application_logs" AND (message="*fastify-reply-from*" AND (url="*../*" OR url="*;*" OR url="*%2f*"))