First published: Thu Nov 04 2021(Updated: )
The agent-to-controller security subsystem limits which files on the Jenkins controller can be accessed by agent processes. Multiple vulnerabilities in the file path filtering implementation of Jenkins 2.318 and earlier, LTS 2.303.2 and earlier allow agent processes to read and write arbitrary files on the Jenkins controller file system, and obtain some information about Jenkins controller file systems. SECURITY-2531 / CVE-2021-21691: Creating symbolic links is possible without the `symlink` permission. We expect that most of these vulnerabilities have been present since [SECURITY-144 was addressed in the 2014-10-30 security advisory](https://www.jenkins.io/security/advisory/2014-10-30/). Jenkins 2.319, LTS 2.303.3 addresses these security vulnerabilities. SECURITY-2531 / CVE-2021-21691: Creating symbolic links now correctly checks the `symlink` permission. As some common operations are now newly subject to access control, it is expected that plugins sending commands from agents to the controller may start failing. Additionally, the newly introduced path canonicalization means that instances using a custom builds directory ([Java system property jenkins.model.Jenkins.buildsDir](https://www.jenkins.io/doc/book/managing/system-properties/#jenkins-model-jenkins-buildsdir)) or partitioning `JENKINS_HOME` using symbolic links may fail access control checks. See [the documentation](https://www.jenkins.io/doc/book/security/controller-isolation/agent-to-controller/#file-access-rules) for how to customize the configuration in case of problems. If you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the [Remoting Security Workaround Plugin](https://www.jenkins.io/redirect/remoting-security-workaround/). It will prevent all agent-to-controller file access using `FilePath` APIs. Because it is more restrictive than Jenkins 2.319, LTS 2.303.3, more plugins are incompatible with it. Make sure to read the plugin documentation before installing it.
Credit: jenkinsci-cert@googlegroups.com jenkinsci-cert@googlegroups.com jenkinsci-cert@googlegroups.com
Affected Software | Affected Version | How to fix |
---|---|---|
Jenkins Jenkins | <2.303.3 | |
Jenkins Jenkins | <2.319 | |
redhat/jenkins | <2.319 | 2.319 |
redhat/jenkins LTS | <2.303.3 | 2.303.3 |
maven/org.jenkins-ci.main:jenkins-core | <=2.303.2 | 2.303.3 |
maven/org.jenkins-ci.main:jenkins-core | >=2.304<=2.318 | 2.319 |
Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.
CVE-2021-21691 is a vulnerability in Jenkins that allows the creation of symbolic links without the proper access control permission.
CVE-2021-21691 has a severity rating of 9.8, which is considered critical.
CVE-2021-21691 affects Jenkins versions 2.318 and earlier, as well as LTS 2.303.2 and earlier.
To fix CVE-2021-21691, you should update Jenkins to version 2.319 or version 2.303.3 for LTS.
You can find more information about CVE-2021-21691 on the Jenkins security advisory and the Red Hat website.