CVE-2021-20195
📋 TL;DR
This vulnerability in Keycloak allows attackers to execute cross-site scripting (XSS) attacks that can lead to complete account takeover. The flaw exists in user-supplied data fields that aren't properly encoded, enabling JavaScript execution. Any Keycloak deployment before version 13.0.0 is affected.
💻 Affected Systems
- Keycloak
📦 What is this software?
Keycloak by Redhat
⚠️ Risk & Real-World Impact
Worst Case
Complete account takeover leading to unauthorized access to all user accounts, data exfiltration, and potential system compromise.
Likely Case
Attackers steal user sessions and credentials, gaining unauthorized access to protected resources and sensitive data.
If Mitigated
Limited impact with proper input validation and output encoding, potentially only affecting individual user sessions.
🎯 Exploit Status
XSS vulnerabilities are commonly exploited, though specific exploit details aren't publicly documented for this CVE.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 13.0.0 or later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1919143
Restart Required: Yes
Instructions:
1. Backup your Keycloak configuration and database. 2. Download Keycloak 13.0.0 or later from the official website. 3. Stop the Keycloak service. 4. Replace the installation with the new version. 5. Restore configuration if needed. 6. Start the Keycloak service. 7. Verify the upgrade was successful.
🔧 Temporary Workarounds
Input Validation Filter
allImplement custom input validation and output encoding for user-supplied data fields
Implement custom servlet filters or security headers like Content-Security-Policy
Web Application Firewall
allDeploy WAF with XSS protection rules to filter malicious payloads
Configure WAF rules to block suspicious JavaScript patterns and encoded payloads
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to prevent inline script execution
- Deploy reverse proxy with XSS filtering capabilities and monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check Keycloak version via admin console or by examining the server startup logs for version informationCheck Version:
Check Keycloak admin console or examine server logs for version stringVerify Fix Applied:
Confirm Keycloak version is 13.0.0 or later and test XSS payloads in user input fields to ensure they're properly sanitized📡 Detection & Monitoring
Log Indicators:
- Unusual JavaScript patterns in user input fields
- Multiple failed login attempts from same session
- Suspicious user agent strings containing script tags
Network Indicators:
- HTTP requests containing script tags or JavaScript in parameters
- Unusual traffic patterns to authentication endpoints
SIEM Query:
source="keycloak" AND (message="*script*" OR message="*javascript*" OR message="*onerror*" OR message="*onload*")