Reflected XSS vulnerability in Jenkins markup formatter preview

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2021-21610: 1.20% estimated exploitation activity in the next 30 days; percentile 68.19 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Jenkins allows administrators to choose the markup formatter to use for descriptions of jobs, builds, views, etc. displayed in Jenkins. When editing such a description, users can choose to have Jenkins render a formatted preview of the description they entered. Jenkins 2.274 and earlier, LTS 2.263.1 and earlier does not implement any restrictions for the URL rendering the formatted preview of markup passed as a query parameter. This results in a reflected cross-site scripting (XSS) vulnerability if the configured markup formatter does not prohibit unsafe elements (JavaScript) in markup, like Anything Goes Formatter Plugin. Jenkins 2.275, LTS 2.263.2 requires that preview URLs are accessed using POST and sets Content-Security-Policy headers that prevent execution of unsafe elements when the URL is accessed directly. In case of problems with this change, these protections can be disabled by setting the Java system properties hudson.markup.MarkupFormatter.previewsAllowGET to true and/or…

Published by the source

24 May 2022, 17:39 UTC

Last modified by the source

14 Dec 2023, 15:39 UTC

Source last checked

26 Oct 2026, 16:21 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7qf3-c2q8-69m3

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# Patch Next advisory brief: CVE-2021-21610

Advisory: Reflected XSS vulnerability in Jenkins markup formatter preview
IDs: CVE-2021-21610, GHSA-7qf3-c2q8-69m3
Record: https://patchnext.com/advisories/cve-2021-21610 (revision 1, source checked 26 Oct 2026, 16:21 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.jenkins-ci.main:jenkins-core 2.275, 2.263.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.jenkins-ci.main:jenkins-core: affected <= 2.263.1; >= 2.264, <= 2.274; fixed in 2.275, 2.263.2

## Suggested inspection (read-only)
- Maven org.jenkins-ci.main:jenkins-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.jenkins-ci.main:jenkins-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-7qf3-c2q8-69m3 (GitHub-reviewed advisory GHSA-7qf3-c2q8-69m3 lists affected ranges: Maven org.jenkins-ci.main:jenkins-core >=0 =2.264 <=2.274)

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