CVE-2021-21696 is a critical-severity (CVSS 9.8) remote code execution vulnerability in org.jenkins-ci.main:jenkins-core. A fix is available for org.jenkins-ci.main:jenkins-core — see the affected versions and patch details below.
Agent-to-controller access control allowed writing to sensitive directory used by Jenkins Pipeline: Shared Groovy Libraries Plugin
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-21696 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
org.jenkins-ci.main:jenkins-core☕org.jenkins-ci.main:jenkins-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.jenkins-ci.main:jenkins-core | all versions | 2.303.3org.jenkins-ci.main:jenkins-core:2.303.3 |
| ☕Maven | org.jenkins-ci.main:jenkins-core | ≥ 2.304&&< 2.319 | 2.319org.jenkins-ci.main:jenkins-core:2.319 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.jenkins-ci.main:jenkins-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.jenkins-ci.main:jenkins-core to 2.303.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21696 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-21696 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-21696. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift Container Platform 3.11 | jenkins-0:2.303.3.1637698110-1.el7 | RHSA-2021:4827 |
| Red Hat OpenShift Container Platform 4.10 | jenkins-0:2.319.2.1643288987-1.el8 | RHSA-2022:0055 |
| Red Hat OpenShift Container Platform 4.6 | jenkins-0:2.303.3.1637597493-1.el8 | RHSA-2021:4799 |
| Red Hat OpenShift Container Platform 4.7 | jenkins-0:2.303.3.1637597018-1.el8 | RHSA-2021:4801 |
| Red Hat OpenShift Container Platform 4.8 | jenkins-0:2.303.3.1637596565-1.el8 | RHSA-2021:4829 |
| Red Hat OpenShift Container Platform 4.9 | jenkins-0:2.303.3.1637595827-1.el8 | RHSA-2021:4833 |
Frequently Asked Questions
Is CVE-2021-21696 in your dependencies?
O3 Security finds CVE-2021-21696 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.