CVE-2021-21610
Reflected XSS vulnerability in Jenkins markup formatter preview
Description
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](https://plugins.jenkins.io/anything-goes-formatter/). 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](https://www.jenkins.io/doc/book/managing/system-properties/) `hudson.markup.MarkupFormatter.previewsAllowGET` to `true` and/or `hudson.markup.MarkupFormatter.previewsSetCSP` to `false`. Doing either is discouraged.
How to fix CVE-2021-21610
To remediate CVE-2021-21610, upgrade the affected package to a fixed version below.
- —upgrade to 2.274.1 or later
- —upgrade to 2.263.2 or later
Is CVE-2021-21610 being exploited?
Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 2.274.1