CVE-2021-21646
📋 TL;DR
This vulnerability in Jenkins Templating Engine Plugin allows attackers with Job/Configure permission to bypass script security protections and execute arbitrary code on the Jenkins controller. This affects Jenkins instances using Templating Engine Plugin version 2.1 or earlier. Attackers can achieve remote code execution in the Jenkins JVM context.
💻 Affected Systems
- Jenkins Templating Engine Plugin
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of Jenkins controller with attacker gaining full control over the Jenkins instance, potentially leading to lateral movement to other systems, data exfiltration, or deployment of persistent backdoors.
Likely Case
Attackers with Job/Configure permission execute arbitrary code to steal credentials, modify pipelines, or disrupt CI/CD operations.
If Mitigated
With proper access controls limiting Job/Configure permissions and network segmentation, impact is limited to authorized users only.
🎯 Exploit Status
Exploitation requires Job/Configure permission. Public exploit details available in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.2 or later
Vendor Advisory: https://www.jenkins.io/security/advisory/2021-04-21/#SECURITY-2311
Restart Required: Yes
Instructions:
1. Update Jenkins Templating Engine Plugin to version 2.2 or later via Jenkins Plugin Manager. 2. Restart Jenkins service. 3. Verify plugin version in Installed Plugins list.
🔧 Temporary Workarounds
Remove Templating Engine Plugin
allUninstall the vulnerable plugin if not required for operations
Manage Jenkins > Manage Plugins > Installed > Templating Engine Plugin > Uninstall
Restrict Job/Configure Permissions
allLimit users with Job/Configure permission to trusted administrators only
Manage Jenkins > Configure Global Security > Authorization > Matrix-based security
🧯 If You Can't Patch
- Implement strict access controls to limit Job/Configure permissions to essential administrators only
- Network segment Jenkins instances and monitor for suspicious pipeline configuration changes
🔍 How to Verify
Check if Vulnerable:
Check Jenkins Plugin Manager for Templating Engine Plugin version. If version is 2.1 or earlier, system is vulnerable.Check Version:
Navigate to Manage Jenkins > Manage Plugins > Installed > Search 'Templating Engine'Verify Fix Applied:
Verify Templating Engine Plugin version is 2.2 or later in Jenkins Plugin Manager.📡 Detection & Monitoring
Log Indicators:
- Unusual pipeline configuration changes
- Script security violations related to Templating Engine
- Unauthorized Groovy script execution
Network Indicators:
- Unexpected outbound connections from Jenkins controller
- Suspicious payloads in Jenkins API requests
SIEM Query:
source="jenkins.log" AND ("Templating Engine" OR "SECURITY-2311" OR "CVE-2021-21646")