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MEDIUM severity

CVE-2021-21615 — jenkins-core

MEDIUM

CVE-2021-21615 is a medium-severity (CVSS 5.3) CWE-367 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.

Time-of-check Time-of-use (TOCTOU) Race Condition in Jenkins

Also known asBIT-jenkins-2021-21615GHSA-qxp6-27gw-99cj
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.9%probability of exploitation in next 30 days
Lower Risk+0.01%
Lower risk than most CVEs60th percentile — riskier than 60% of all scored CVEsHighest risk
0.00%0.47%0.94%1.41%0.4%0.9%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

Due to a time-of-check to time-of-use (TOCTOU) race condition, the file browser for workspaces, archived artifacts, and $JENKINS_HOME/userContent/ follows symbolic links to locations outside the directory being browsed in Jenkins 2.275 and LTS 2.263.2.

This allows attackers with Job/Workspace permission and the ability to control workspace contents, e.g., with Job/Configure permission or the ability to change SCM contents, to create symbolic links that allow them to access files outside workspaces using the workspace browser.

This issue is caused by an incorrectly applied fix for SECURITY-1452 / CVE-2021-21602 in the 2021-01-13 security advisory.

Jenkins 2.276, LTS 2.263.3 no longer differentiates the check and the use of symlinks in workspace browsers.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.jenkins-ci.main:jenkins-coreall versions2.263.3org.jenkins-ci.main:jenkins-core:2.263.3
☕Mavenorg.jenkins-ci.main:jenkins-core≥ 2.264&&< 2.2762.276org.jenkins-ci.main:jenkins-core:2.276

Affected Products

1 product · 2 configurations
Application
jenkinsjenkins
< 2.276
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 2.263.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21615 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 HatModerate
ProductFixed inAdvisory
Red Hat OpenShift Container Platform 4.5conmon-2:2.0.21-1.rhaos4.5.el7RHSA-2021:0429
Red Hat OpenShift Container Platform 4.6jenkins-0:2.263.3.1612434510-1.el8RHSA-2021:0423

Frequently Asked Questions

Due to a time-of-check to time-of-use (TOCTOU) race condition, the file browser for workspaces, archived artifacts, and `$JENKINS_HOME/userContent/` follows symbolic links to locations outside the directory being browsed in Jenkins 2.275 and LTS 2.263.2. This allows attackers with Job/Workspace permission and the ability to control workspace contents, e.g., with Job/Configure permission or the ability to change SCM contents, to create symbolic links that allow them to access files outside workspaces using the workspace browser. This issue is caused by an incorrectly applied fix for SECURITY-
O3 Security · Impact-Aware SCA

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CVE-2021-21615: jenkins-core — Fixed in 2.263.3