CVE-2026-25545
📋 TL;DR
This SSRF vulnerability in Astro web framework allows attackers to redirect error page requests to internal network resources by manipulating the Host header. It affects Server-Side Rendered applications using custom error pages without proper Host header validation. Attackers can potentially access cloud metadata services and internal network resources.
💻 Affected Systems
- Astro web framework
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete internal network compromise including access to cloud metadata services, internal APIs, databases, and localhost services, potentially leading to data exfiltration or lateral movement.
Likely Case
Access to internal services and cloud metadata, potentially exposing sensitive configuration data or internal APIs.
If Mitigated
Limited to accessing only publicly exposed internal services if proper network segmentation exists.
🎯 Exploit Status
Exploitation requires direct server access bypassing proxy validation, which can be achieved through origin IP discovery or default configurations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 9.5.4
Vendor Advisory: https://github.com/withastro/astro/security/advisories/GHSA-qq67-mvv5-fw3g
Restart Required: Yes
Instructions:
1. Update Astro to version 9.5.4 or later using npm update @astrojs/node@9.5.4
2. Restart the application server
3. Verify the update was successful
🔧 Temporary Workarounds
Host Header Validation
allImplement middleware to validate Host headers against allowed domains
Implement custom middleware to check req.headers.host against allowed list
Proxy Configuration
allEnsure proper proxy configuration validates Host headers before reaching application
Configure reverse proxy (nginx/apache) to validate Host headers
🧯 If You Can't Patch
- Implement strict network segmentation to isolate internal services from application servers
- Deploy WAF rules to block suspicious Host header patterns and redirect attempts
🔍 How to Verify
Check if Vulnerable:
Check Astro version and verify if using custom error pages with SSRCheck Version:
npm list @astrojs/node | grep @astrojs/nodeVerify Fix Applied:
Confirm Astro version is 9.5.4 or later and test SSRF attempts are blocked📡 Detection & Monitoring
Log Indicators:
- Unusual Host header values in error page requests
- Multiple requests to /500.html with varying Host headers
- Outbound requests from application to internal IPs
Network Indicators:
- HTTP requests with manipulated Host headers to error endpoints
- Application server making unexpected outbound connections to internal networks
SIEM Query:
source="astro_app" AND (uri="/500.html" OR uri="/404.html") AND host_header NOT IN ["allowed_domains"]