1. Introduction
Jenkins Security Advisory 2019-01-08 details multiple vulnerabilities affecting Jenkins job scheduling and management systems. These flaws could allow attackers to execute arbitrary code on the Jenkins master JVM, potentially compromising the entire system. Systems running vulnerable versions of Script Security Plugin, Pipeline: Groovy Plugin, or Pipeline: Declarative Plugin are at risk. This vulnerability poses a high impact to confidentiality, integrity, and availability.
2. Technical Explanation
The vulnerabilities stem from sandbox bypasses within several Jenkins plugins. Attackers who can provide sandboxed scripts or pipeline code with Overall/Read permissions can execute arbitrary code on the Jenkins master JVM. This is due to insufficient restrictions in how these plugins handle untrusted input. CVE-2019-1003000 affects Script Security Plugin, CVE-2019-1003001 affects Pipeline: Groovy Plugin, and CVE-2019-1003002 affects Pipeline: Declarative Plugin.
- Root cause: The plugins do not adequately sanitize or restrict the execution of sandboxed scripts and pipeline code.
- Exploit mechanism: An attacker provides a malicious script through an HTTP endpoint, which bypasses the sandbox and executes arbitrary code on the Jenkins master JVM.
- Scope: Affected versions include Script Security Plugin 1.49 and earlier, Pipeline: Groovy Plugin 2.61 and earlier, and Pipeline: Declarative Plugin 1.3.3 and earlier.
3. Detection and Assessment
Confirming vulnerability requires checking the installed plugin versions on your Jenkins instance. A thorough assessment involves reviewing pipeline scripts for potentially malicious code.
- Quick checks: Check the installed plugin versions in the Jenkins UI under Manage Jenkins > Plugins.
- Scanning: Nessus and other vulnerability scanners may identify these vulnerabilities using specific plugin IDs. These are examples only, as scanner coverage varies.
- Logs and evidence: Review Jenkins logs for unusual script execution or errors related to sandbox bypasses. Look in the Jenkins master log files.
# Example command placeholder:
# No direct command exists to check plugin versions from the CLI. Use the UI as described above.
4. Solution / Remediation Steps
The primary solution is to upgrade affected plugins to the latest secure versions. Follow these steps carefully.
4.1 Preparation
- Ensure you have sufficient disk space for plugin upgrades. A roll back plan involves restoring from the pre-upgrade backup.
- A change window may be required, depending on service criticality and impact. Approval from a senior administrator is recommended.
4.2 Implementation
- Step 1: Update Script Security Plugin to the latest version via Manage Jenkins > Plugins > Available.
- Step 2: Update Pipeline: Groovy Plugin to the latest version via Manage Jenkins > Plugins > Available.
- Step 3: Update Pipeline: Declarative Plugin to the latest version via Manage Jenkins > Plugins > Available.
4.3 Config or Code Example
Before
# Script Security Plugin version 1.49 or earlier
# Pipeline: Groovy Plugin version 2.61 or earlier
# Pipeline: Declarative Plugin version 1.3.3 or earlier
After
# Script Security Plugin latest version (e.g., 1.70)
# Pipeline: Groovy Plugin latest version (e.g., 2.84)
# Pipeline: Declarative Plugin latest version (e.g., 1.56)
4.4 Security Practices Relevant to This Vulnerability
Several security practices can help mitigate this type of vulnerability.
- Practice 1: Least privilege – limit user permissions to only what is necessary, reducing the impact if an attacker gains access.
- Practice 2: Input validation – carefully validate all input data to prevent malicious code from being injected into scripts and pipelines.
4.5 Automation (Optional)
If you use a configuration management tool like Ansible, you can automate plugin upgrades.
# Example Ansible playbook snippet:
- name: Upgrade Jenkins plugins
community.general.jenkins_plugin:
name: "{{ item }}"
state: latest
loop:
- script-security
- pipeline-groovy
- pipeline-declarative
5. Verification / Validation
Confirm the fix by verifying the plugin versions and retesting for vulnerability.
- Post-fix check: Check the installed plugin versions in the Jenkins UI under Manage Jenkins > Plugins to ensure they are updated.
- Re-test: Re-run the initial version checks to confirm that all plugins are now at or above the secure versions.
- Monitoring: Monitor Jenkins logs for any errors related to plugin execution, which could indicate a regression.
# Post-fix command and expected output
# No direct CLI command exists. Check UI versions as described above. Expected output should show latest versions of plugins.
6. Preventive Measures and Monitoring
Proactive measures can help prevent similar vulnerabilities in the future.
- Baselines: Update your security baseline to include minimum plugin version requirements for Jenkins components.
- Pipelines: Integrate Static Application Security Testing (SAST) into your CI/CD pipeline to identify potentially vulnerable code in pipeline scripts.
- Asset and patch process: Implement a regular patch management cycle for Jenkins plugins, ensuring timely updates to address security vulnerabilities.
7. Risks, Side Effects, and Roll Back
Plugin upgrades can sometimes introduce compatibility issues.
- Risk or side effect 1: Plugin upgrade may cause temporary pipeline failures due to incompatible changes. Mitigation: Test the upgrade in a non-production environment first.
- Risk or side effect 2: Jenkins restart may cause brief service downtime. Mitigation: Schedule the upgrade during off-peak hours.
- Roll back: Restore your Jenkins instance from the pre-upgrade backup if compatibility issues arise.
8. References and Resources
- Vendor advisory or bulletin: https://jenkins.io/security/advisory/2019-01-08/
- NVD or CVE entry: N/A – multiple CVEs are listed in the advisory.
- Product or platform documentation relevant to the fix: https://www.jenkins.io/doc/book/managing-plugins/