CVE-2021-21696 Explained : Impact and Mitigation

Jenkins 2.318 and earlier, LTS 2.303.2 and earlier versions are vulnerable to a security issue that allows attackers to execute unsandboxed code in the Jenkins controller process. This CVE, assigned on November 4, 2021, has been identified as CVE-2021-21696.

Understanding CVE-2021-21696

This section provides insight into the nature and impact of CVE-2021-21696.

What is CVE-2021-21696?

CVE-2021-21696 affects Jenkins versions 2.318 and earlier, LTS 2.303.2 and earlier, enabling attackers controlling agent processes to replace trusted library code with malicious variants, leading to unsandboxed code execution in the Jenkins controller process.

The Impact of CVE-2021-21696

The security vulnerability in Jenkins allows threat actors to tamper with trusted library code within build directories, resulting in the execution of unauthorized code within the Jenkins controller process.

Technical Details of CVE-2021-21696

This section delves into the technical aspects of CVE-2021-21696.

Vulnerability Description

The flaw in Jenkins versions prior to 2.318 and LTS 2.303.2 allows agent processes to manipulate libraries within build directories, potentially leading to unauthorized code execution in the Jenkins controller process.

Affected Systems and Versions

Products impacted include Jenkins with versions less than or equal to 2.318 and LTS less than or equal to 2.303.2, irrespective of custom or unspecified installations.

Exploitation Mechanism

Attackers gaining control of agent processes can exploit the vulnerability by replacing trusted library code in the libs/ directory of build directories, enabling the execution of unsandboxed code on the Jenkins controller.

Mitigation and Prevention

This section outlines the necessary steps to address and prevent the exploitation of CVE-2021-21696.

Immediate Steps to Take

Users are advised to update Jenkins to versions beyond 2.318 and LTS versions beyond 2.303.2 to eliminate the vulnerability and prevent unauthorized code execution.

Long-Term Security Practices

Incorporating continuous monitoring of Jenkins security advisories, maintaining up-to-date software versions, and implementing robust access control measures can bolster the overall security posture.

Patching and Updates

Regularly check for security updates from Jenkins project, apply patches promptly, and follow best practices to secure Jenkins deployments.