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MEDIUM severity

CVE-2021-21673 — cas-plugin

MEDIUMFix: jenkinsci/cas-plugin@8ac536a

CVE-2021-21673 is a medium-severity (CVSS 6.1) vulnerability in org.jenkins-ci.plugins:cas-plugin. A fix is available for org.jenkins-ci.plugins:cas-plugin — see the affected versions and patch details below.

Open redirect vulnerability in Jenkins CAS Plugin

Also known asGHSA-2vvr-5757-qp87
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 28, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs75th percentile — riskier than 75% of all scored CVEsHighest risk
0.00%0.69%1.39%2.08%0.1%1.6%Apr 26Aug 26Oct 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

1 pkg affected
☕org.jenkins-ci.plugins:cas-plugin

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 CAS Plugin 1.6.0 and earlier improperly determines that a redirect URL after login is legitimately pointing to Jenkins.

This allows attackers to perform phishing attacks by having users go to a Jenkins URL that will forward them to a different site after successful authentication.

Jenkins CAS Plugin 1.6.1 only redirects to relative (Jenkins) URLs.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.jenkins-ci.plugins:cas-pluginall versions1.6.1org.jenkins-ci.plugins:cas-plugin:1.6.1

Affected Products

1 product · 1 configurations
Application
casjenkins
≤ 1.6.0
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.plugins:cas-plugin, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.jenkins-ci.plugins:cas-plugin to 1.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21673 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.

Frequently Asked Questions

Jenkins CAS Plugin 1.6.0 and earlier improperly determines that a redirect URL after login is legitimately pointing to Jenkins. This allows attackers to perform phishing attacks by having users go to a Jenkins URL that will forward them to a different site after successful authentication. Jenkins CAS Plugin 1.6.1 only redirects to relative (Jenkins) URLs.
O3 Security · Impact-Aware SCA

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CVE-2021-21673: cas-plugin — Fixed in 1.6.1