{"cve":"CVE-2021-21391","nvd":{"published":"2021-04-29T01:15:07.883","modified":"2026-06-17T03:35:28.500","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-400"],"references":["https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-3rh3-wfr4-76mj","https://www.npmjs.com/package/%40ckeditor/ckeditor5-engine","https://www.npmjs.com/package/%40ckeditor/ckeditor5-font","https://www.npmjs.com/package/%40ckeditor/ckeditor5-image","https://www.npmjs.com/package/%40ckeditor/ckeditor5-list"],"products":["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"],"source":"nvd","synced_at":"2026-10-19T21:18:09.669877188+00:00"},"epss":{"cve":"CVE-2021-21391","score":0.01667,"percentile":0.76759,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-3rh3-wfr4-76mj","url":"https://osv.dev/vulnerability/GHSA-3rh3-wfr4-76mj","summary":"Regular expression Denial of Service in multiple packages","modified":"2026-07-08T06:27:26.938294321Z","packages":[{"ecosystem":"npm","name":"@ckeditor/ckeditor5-engine","purl":"pkg:npm/%40ckeditor/ckeditor5-engine","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-font","purl":"pkg:npm/%40ckeditor/ckeditor5-font","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-image","purl":"pkg:npm/%40ckeditor/ckeditor5-image","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-list","purl":"pkg:npm/%40ckeditor/ckeditor5-list","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-markdown-gfm","purl":"pkg:npm/%40ckeditor/ckeditor5-markdown-gfm","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-media-embed","purl":"pkg:npm/%40ckeditor/ckeditor5-media-embed","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-paste-from-office","purl":"pkg:npm/%40ckeditor/ckeditor5-paste-from-office","ranges":["<27.0.0"],"fixed":["27.0.0"]},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-widget","purl":"pkg:npm/%40ckeditor/ckeditor5-widget","ranges":["<27.0.0"],"fixed":["27.0.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}