CVE-2021-21671 Explained : Impact and Mitigation

Jenkins 2.299 and earlier, LTS 2.289.1 and earlier versions do not invalidate the previous session on login.

Understanding CVE-2021-21671

This CVE affects Jenkins, specifically versions 2.266 and LTS 2.277.1, including earlier versions.

What is CVE-2021-21671?

CVE-2021-21671 is a vulnerability in Jenkins that allows attackers to maintain the user's session after the user logs out, leading to potential security risks.

The Impact of CVE-2021-21671

The vulnerability in Jenkins can be exploited by malicious actors to carry out unauthorized actions with the user's session, compromising the security and integrity of the system.

Technical Details of CVE-2021-21671

The technical details of the CVE include:

Vulnerability Description

Jenkins versions 2.299 and earlier, LTS 2.289.1 and earlier, fail to invalidate the user session upon logout, allowing attackers to exploit active user sessions.

Affected Systems and Versions

Jenkins versions affected by CVE-2021-21671 include 2.266, LTS 2.277.1, and earlier versions.

Exploitation Mechanism

Attackers can exploit this vulnerability by maintaining an active user session post-logout, enabling unauthorized access and actions within the system.

Mitigation and Prevention

To safeguard systems from CVE-2021-21671, consider the following measures:

Immediate Steps to Take

Upgrade Jenkins to a version that includes a fix for the session fixation vulnerability.
Implement additional authentication measures.

Long-Term Security Practices

Regularly monitor and update Jenkins installations.
Educate users on best practices regarding session security.

Patching and Updates

Apply security patches provided by Jenkins to address the vulnerability.
Stay informed about security advisories and updates issued by the Jenkins project.