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MEDIUM severity

CVE-2021-21660 — markdown-formatter

MEDIUMFix: jenkinsci/markdown-formatter-plugin@6b283a5

CVE-2021-21660 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in io.jenkins.plugins:markdown-formatter. A fix is available for io.jenkins.plugins:markdown-formatter — see the affected versions and patch details below.

XSS vulnerability in Jenkins Markdown Formatter Plugin

Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs65th percentile — riskier than 65% of all scored CVEsHighest risk
0.00%0.53%1.06%1.59%0.2%1.1%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

1 pkg affected
☕io.jenkins.plugins:markdown-formatter

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 Markdown Formatter Plugin 0.1.0 and earlier uses a Markdown library to parse Markdown that does not escape crafted link target URLs.

This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers with the ability to edit any description rendered using the configured markup formatter.

Jenkins Markdown Formatter Plugin 0.2.0 uses a different Markdown library that is not affected by this problem.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenio.jenkins.plugins:markdown-formatterall versions0.2.0io.jenkins.plugins:markdown-formatter:0.2.0

Affected Products

1 product · 1 configurations
Application
markdown formatterjenkins
≤ 0.1.0
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 io.jenkins.plugins:markdown-formatter, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update io.jenkins.plugins:markdown-formatter to 0.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21660 is resolved across your whole dependency graph.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

Jenkins Markdown Formatter Plugin 0.1.0 and earlier uses a Markdown library to parse Markdown that does not escape crafted link target URLs. This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers with the ability to edit any description rendered using the configured markup formatter. Jenkins Markdown Formatter Plugin 0.2.0 uses a different Markdown library that is not affected by this problem.
O3 Security · Impact-Aware SCA

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CVE-2021-21660: markdown-formatter XSS — Fixed in 0.2.0