CVE-2021-39497
📋 TL;DR
CVE-2021-39497 is a Server-Side Request Forgery (SSRF) vulnerability in eyoucms 1.5.4 that allows attackers to inject URLs via the saveRemote() function, potentially accessing internal systems. This affects all deployments of eyoucms 1.5.4 that expose the vulnerable functionality. Attackers can exploit this to scan internal networks or access restricted resources.
💻 Affected Systems
- eyoucms
📦 What is this software?
Eyoucms by Eyoucms
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains access to internal systems, exfiltrates sensitive data, or pivots to other critical infrastructure.
Likely Case
Attacker scans internal network, accesses metadata services, or interacts with internal APIs.
If Mitigated
Limited to accessing only allowed external resources with proper input validation.
🎯 Exploit Status
Proof of concept available in GitHub repositories, exploitation requires minimal technical skill.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.5.5 and later
Vendor Advisory: https://github.com/eyoucms/eyoucms/releases/tag/v1.5.4
Restart Required: No
Instructions:
1. Download latest version from GitHub releases. 2. Backup current installation. 3. Replace vulnerable files with patched version. 4. Verify functionality.
🔧 Temporary Workarounds
Input Validation Filter
allAdd input validation to sanitize URLs before processing in saveRemote() function.
Modify saveRemote() function to validate URL scheme, host, and restrict to allowed domains
Network Segmentation
allRestrict outbound connections from the CMS server to prevent internal network access.
Configure firewall to block outbound connections from CMS server to internal IP ranges
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block SSRF patterns
- Disable or restrict the saveRemote() function if not required
🔍 How to Verify
Check if Vulnerable:
Check if running eyoucms version 1.5.4 and examine saveRemote() function for input validation.Check Version:
Check eyoucms version in admin panel or examine version files in installation directory.Verify Fix Applied:
Test with controlled SSRF payloads to confirm they are blocked or properly validated.📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from CMS server
- Requests to internal IP addresses or metadata services
Network Indicators:
- HTTP requests from CMS server to internal network ranges
- Requests to cloud metadata endpoints
SIEM Query:
source_ip="CMS_SERVER_IP" AND (dest_ip="169.254.169.254" OR dest_ip="10.*" OR dest_ip="192.168.*" OR dest_ip="172.16-31.*")