CVE-2021-39500
📋 TL;DR
Eyoucms 1.5.4 contains a directory traversal vulnerability that allows attackers to write files outside intended directories by injecting '../' sequences in parameters. This affects all systems running Eyoucms 1.5.4 with default configurations.
💻 Affected Systems
- Eyoucms
📦 What is this software?
Eyoucms by Eyoucms
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise if attacker can write executable files to web-accessible directories.
Likely Case
Arbitrary file write allowing defacement, data theft, or privilege escalation by overwriting configuration files.
If Mitigated
Limited impact if file permissions restrict write access to critical directories.
🎯 Exploit Status
Simple path traversal payloads work without authentication. Public exploit code exists in GitHub repositories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.5.5 or later
Vendor Advisory: https://github.com/eyoucms/eyoucms/releases/tag/v1.5.4
Restart Required: No
Instructions:
1. Download latest version from official GitHub releases. 2. Backup current installation. 3. Replace vulnerable files with patched version. 4. Verify input validation is working.
🔧 Temporary Workarounds
Input Validation Filter
allAdd server-side validation to block '../' sequences in tpldir, filename, type, and nid parameters
Modify application code to sanitize user input before processing file operations
Web Application Firewall Rule
allBlock requests containing directory traversal patterns
Add WAF rule to block requests with '../' in URL parameters
🧯 If You Can't Patch
- Restrict file permissions to prevent writing outside intended directories
- Implement strict input validation at the web server level using mod_security or similar
🔍 How to Verify
Check if Vulnerable:
Test by sending requests with '../' sequences in tpldir, filename, type, or nid parameters and observe if file operations succeed outside intended directories.Check Version:
Check admin panel or view source code version informationVerify Fix Applied:
Attempt same traversal attacks after patch - should be blocked or sanitized. Check version number in admin panel.📡 Detection & Monitoring
Log Indicators:
- HTTP requests containing '../' sequences in parameters
- File write operations to unexpected directories
- Failed file operations with traversal attempts
Network Indicators:
- HTTP requests with encoded traversal sequences (%2e%2e%2f)
- Multiple failed file operations followed by successful writes
SIEM Query:
web.url:*%2e%2e%2f* OR web.uri:*../* AND (web.param:tpldir OR web.param:filename OR web.param:type OR web.param:nid)