CVE-2021-21660Network attack vector

Stored XSS via unsanitized Markdown link targets

Published May 25, 2021 · Updated Aug 3, 2024

Stored XSS in Jenkins Markdown Formatter Plugin 0.1.0 and earlier allows remote authenticated users to execute script via crafted link targets. MarkdownFormatter.translate renders Flexmark link destinations into href attributes without sanitizing dangerous URL schemes, including encoded javascript targets. The attacker must be able to edit a description rendered by the configured formatter, and a user must view it for the script to run in the Jenkins origin.

CVSS severity5.4
Medium
EPSS probability1.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Stored XSS in Jenkins Markdown Formatter Plugin 0.1.0 and earlier allows remote authenticated users to execute script via crafted link targets. MarkdownFormatter.translate renders Flexmark link destinations into href attributes without sanitizing dangerous URL schemes, including encoded javascript targets. The attacker must be able to edit a description rendered by the configured formatter, and a user must view it for the script to run in the Jenkins origin.

The record

CVE
CVE-2021-21660
Published
May 25, 2021
Updated
Aug 3, 2024
Vendor
Jenkins Project
Product
Markdown Formatter Plugin
Classifications
CWE-79, CAPEC-592, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=0.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Jenkins Project · Markdown Formatter Pluginversion=unspecified <=0.1.0

Published CVSS scores

5.4GitHub Security AdvisoryCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CAPEC-592Stored XSS
T1059.007Command and Scripting Interpreter: JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo