{"id":"CVE-2021-21610","aliases":["BIT-jenkins-2021-21610","GHSA-7qf3-c2q8-69m3"],"url":"https://o3.security/vulnerability/CVE-2021-21610","summary":"Reflected XSS vulnerability in Jenkins markup formatter preview","details":"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.\n\nJenkins 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/).\n\nJenkins 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.\n\nIn 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.","published":"2021-01-13T16:15:14.007Z","modified":"2026-07-08T21:25:43.501865Z","cvss":{"score":6.1,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"org.jenkins-ci.main:jenkins-core","fixedVersion":"2.263.2"},{"ecosystem":"Maven","name":"org.jenkins-ci.main:jenkins-core","fixedVersion":"2.275"}],"fix":{"url":"https://github.com/jenkinsci/jenkins/commit/89ec0c40b68cd1e4e9f9ef5ebcafd87e7fa16589","label":"jenkinsci/jenkins@89ec0c4"},"references":[{"type":"ADVISORY","url":"https://www.jenkins.io/security/advisory/2021-01-13/#SECURITY-2153"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21610"},{"type":"WEB","url":"https://github.com/jenkinsci/jenkins/commit/89ec0c40b68cd1e4e9f9ef5ebcafd87e7fa16589"},{"type":"PACKAGE","url":"https://github.com/jenkinsci/jenkins"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-08T21:25:43.501865Z"}}