{"id":"CVE-2021-21391","url":"https://www.cyber-defence.io/tools/cve/CVE-2021-21391","generatedAt":"2026-10-28T02:57:47.633Z","title":"Following an internal audit, a regular expression denial of service (ReDoS) vulnerability has been discovered in multiple CKEditor 5 packages.","description":"CKEditor 5 provides a WYSIWYG editing solution. This CVE affects the following npm packages: ckeditor5-engine, ckeditor5-font, ckeditor5-image, ckeditor5-list, ckeditor5-markdown-gfm, ckeditor5-media-embed, ckeditor5-paste-from-office, and ckeditor5-widget. Following an internal audit, a regular expression denial of service (ReDoS) vulnerability has been discovered in multiple CKEditor 5 packages. The vulnerability allowed to abuse particular regular expressions, which could cause a significant performance drop resulting in a browser tab freeze. It affects all users using the CKEditor 5 packages listed above at version <= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","published":"2021-04-29T01:15:08.000Z","lastModified":"2026-06-17T03:35:29.000Z","status":"Modified","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"3.1","score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H"},"cwe":["CWE-400"],"affected":["ckeditor/ckeditor5-engine","ckeditor/ckeditor5-font","ckeditor/ckeditor5-image","ckeditor/ckeditor5-list","ckeditor/ckeditor5-markdown-gfm","ckeditor/ckeditor5-media-embed","ckeditor/ckeditor5-paste-from-office","ckeditor/ckeditor5-widget"],"epss":{"score":0.01667,"percentile":0.76599,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (1.67%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-3rh3-wfr4-76mj","tags":["Third Party Advisory"],"source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-engine","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-font","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-image","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-list","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-media-embed","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-paste-from-office","source":"security-advisories@github.com"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-widget","source":"security-advisories@github.com"},{"url":"https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-3rh3-wfr4-76mj","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-engine","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-font","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-image","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-list","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-media-embed","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-paste-from-office","source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-widget","source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-21391","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}