CVE-2021-21696

Jenkins 2.318 and earlier, LTS 2.303.2 and earlier does not limit agent read/write access to the libs/ directory inside build directories when using the FilePath APIs. This directory is used by the Pipeline: Shared Groovy Libraries Plugin to store copies of shared libraries.

This allows attackers in control of agent processes to replace the code of a trusted library with a modified variant, resulting in unsandboxed code execution in the Jenkins controller process.

Jenkins 2.319, LTS 2.303.3 prohibits agent read/write access to the libs/ directory inside build directories.

If you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the Remoting Security Workaround Plugin. 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.

It is not easily possible to customize the file access rules to prohibit access to the libs/ directory specifically, as built-in rules (granting access to <BUILDDIR> contents) would take precedence over a custom rule prohibiting access.

CVE-2021-21696 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.319, 2.303.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2021-21696? CVE-2021-21696 is a high-severity security vulnerability in org.jenkins-ci.main:jenkins-core (maven), affecting versions >= 2.304, <= 2.318. It is fixed in 2.319, 2.303.3.
2. How severe is CVE-2021-21696? CVE-2021-21696 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of org.jenkins-ci.main:jenkins-core are affected by CVE-2021-21696? org.jenkins-ci.main:jenkins-core (maven) versions >= 2.304, <= 2.318 is affected.
4. Is there a fix for CVE-2021-21696? Yes. CVE-2021-21696 is fixed in 2.319, 2.303.3. Upgrade to this version or later.
5. Is CVE-2021-21696 exploitable, and should I be worried? Whether CVE-2021-21696 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-21696 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-21696?
   • Upgrade org.jenkins-ci.main:jenkins-core to 2.319 or later
   • Upgrade org.jenkins-ci.main:jenkins-core to 2.303.3 or later

Other vulnerabilities in org.jenkins-ci.main:jenkins-core