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MEDIUM severity

CVE-2021-21606 — jenkins-core

MEDIUMFix: jenkinsci/jenkins@f576b2e

CVE-2021-21606 is a medium-severity (CVSS 4.3) Improper Input Validation 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.

Arbitrary file existence check in file fingerprints in Jenkins

Also known asBIT-jenkins-2021-21606GHSA-f585-9fw3-rj2m
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs69th percentile — riskier than 69% of all scored CVEsHighest risk
0.00%0.58%1.15%1.73%0.2%1.2%May 26Sep 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 provides a feature for jobs to store and track fingerprints of files used during a build. Jenkins 2.274 and earlier, LTS 2.263.1 and earlier provides a REST API to check where a given fingerprint was used by which builds. This endpoint does not fully validate that the provided fingerprint ID is properly formatted before checking for the XML metadata for that fingerprint on the controller file system.

This allows attackers with Overall/Read permission to check for the existence of XML files on the controller file system where the relative path can be constructed as 32 characters.

Jenkins 2.275, LTS 2.263.2 validates that a fingerprint ID is properly formatted before checking for its existence.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.jenkins-ci.main:jenkins-coreall versions2.263.2org.jenkins-ci.main:jenkins-core:2.263.2
☕Mavenorg.jenkins-ci.main:jenkins-core≥ 2.264&&< 2.2752.275org.jenkins-ci.main:jenkins-core:2.275

Affected Products

1 product · 2 configurations
Application
jenkinsjenkins
≤ 2.274
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 2.263.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21606 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 3.11jenkins-0:2.263.3.1612433584-1.el7RHSA-2021:0637
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
Red Hat OpenShift Container Platform 4.8atomic-openshift-service-idler-0:4.8.0-202106281541.p0.git.39cfc66.assembly.stream.el8RHSA-2021:2437

Frequently Asked Questions

Jenkins provides a feature for jobs to store and track fingerprints of files used during a build. Jenkins 2.274 and earlier, LTS 2.263.1 and earlier provides a REST API to check where a given fingerprint was used by which builds. This endpoint does not fully validate that the provided fingerprint ID is properly formatted before checking for the XML metadata for that fingerprint on the controller file system. This allows attackers with Overall/Read permission to check for the existence of XML files on the controller file system where the relative path can be constructed as 32 characters. Jenk
O3 Security · Impact-Aware SCA

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CVE-2021-21606: jenkins-core — Fixed in 2.263.2