CVE-2021-27581
📋 TL;DR
This SQL injection vulnerability in Kentico CMS allows attackers to execute arbitrary SQL commands via the tagname parameter in the Blog module. It affects Kentico CMS 5.5 R2 installations, potentially leading to data theft, modification, or complete system compromise. Organizations running vulnerable versions are at risk.
💻 Affected Systems
- Kentico CMS
📦 What is this software?
Kentico Cms by Kentico
⚠️ Risk & Real-World Impact
Worst Case
Complete database compromise including data exfiltration, data destruction, privilege escalation to administrative access, and potential remote code execution on the underlying server.
Likely Case
Unauthorized access to sensitive data stored in the database, including user credentials, personal information, and content management data.
If Mitigated
Limited impact with proper input validation and parameterized queries preventing SQL injection, though the vulnerability still exists in the codebase.
🎯 Exploit Status
SQL injection via tagname parameter is straightforward to exploit. Public proof-of-concept code exists demonstrating the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to Kentico CMS version 13 or migrate to Kentico Xperience (successor product)
Vendor Advisory: https://kontent.ai
Restart Required: Yes
Instructions:
1. Backup your Kentico CMS installation and database. 2. Upgrade to Kentico CMS version 13 or migrate to Kentico Xperience. 3. Apply the update following Kentico's upgrade documentation. 4. Restart the application and web server. 5. Test functionality of the Blog module.
🔧 Temporary Workarounds
Input Validation Filter
allImplement server-side input validation to sanitize the tagname parameter before processing
Implement parameterized queries in the Blog module code
Add input validation to reject SQL special characters in tagname parameter
Web Application Firewall Rules
allConfigure WAF to block SQL injection patterns in tagname parameter requests
Configure WAF to detect and block SQL injection patterns in URL parameters
Set up rules to monitor for unusual database query patterns
🧯 If You Can't Patch
- Implement network segmentation to isolate the Kentico CMS server from sensitive systems
- Deploy a web application firewall with SQL injection protection rules
🔍 How to Verify
Check if Vulnerable:
Check if your Kentico CMS version is 5.5 R2 build 5.5.3996 by examining the installation or checking the admin interface version information.Check Version:
Check Kentico CMS admin panel or examine web.config/installation files for version informationVerify Fix Applied:
After patching, test the Blog module functionality and attempt to reproduce the SQL injection using the tagname parameter to confirm it's no longer vulnerable.📡 Detection & Monitoring
Log Indicators:
- Unusual SQL queries in database logs
- Multiple failed login attempts following SQL injection patterns
- Unexpected database schema changes
Network Indicators:
- HTTP requests with SQL injection patterns in tagname parameter
- Unusual outbound database connections from web server
SIEM Query:
source="web_server_logs" AND (uri="*tagname=*" AND (uri="*' OR *" OR uri="*;--*" OR uri="*UNION*"))