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CRITICAL severity

CVE-2021-21696 — jenkins-core

CRITICALFix: jenkinsci/jenkins@93451e2

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

Also known asBIT-jenkins-2021-21696GHSA-c5r9-rx53-q3gf
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 1, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
2.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs84th percentile — riskier than 84% of all scored CVEsHighest risk
0.45%1.27%2.08%2.90%1.0%2.4%May 26Aug 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected
☕org.jenkins-ci.main:jenkins-core☕org.jenkins-ci.main:jenkins-core

Real-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

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.jenkins-ci.main:jenkins-coreall versions2.303.3org.jenkins-ci.main:jenkins-core:2.303.3
☕Mavenorg.jenkins-ci.main:jenkins-core≥ 2.304&&< 2.3192.319org.jenkins-ci.main:jenkins-core:2.319

Affected Products

1 product · 2 configurations
Application
jenkinsjenkins
≤ 2.318
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    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.

  2. 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.

  3. 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.

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.

Red HatImportant
Workaround published by Red Hat
Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update the affected package as soon as possible.
Source: Red Hat security advisory for CVE-2021-21696 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat OpenShift Container Platform 3.11jenkins-0:2.303.3.1637698110-1.el7RHSA-2021:4827
Red Hat OpenShift Container Platform 4.10jenkins-0:2.319.2.1643288987-1.el8RHSA-2022:0055
Red Hat OpenShift Container Platform 4.6jenkins-0:2.303.3.1637597493-1.el8RHSA-2021:4799
Red Hat OpenShift Container Platform 4.7jenkins-0:2.303.3.1637597018-1.el8RHSA-2021:4801
Red Hat OpenShift Container Platform 4.8jenkins-0:2.303.3.1637596565-1.el8RHSA-2021:4829
Red Hat OpenShift Container Platform 4.9jenkins-0:2.303.3.1637595827-1.el8RHSA-2021:4833

Frequently Asked Questions

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 u
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CVE-2021-21696: jenkins-core — Fixed in 2.303.3