{"id":"CVE-2021-21391","aliases":["GHSA-3rh3-wfr4-76mj"],"url":"https://o3.security/vulnerability/CVE-2021-21391","summary":"Regular expression Denial of Service in multiple packages","details":"\n### Impact\nA 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.\n\n### Patches\nThe problem has been recognized and patched. The fix will be available in version 27.0.0.\n\n### For more information\nEmail us at security@cksource.com if you have any questions or comments about this advisory.\n\n### Acknowledgements\nThe CKEditor 5 team would like to thank Yeting Li for recognizing and reporting these vulnerabilities.","published":"2021-04-29T01:15:07.883Z","modified":"2026-07-09T12:20:00.183386Z","cvss":{"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"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@ckeditor/ckeditor5-engine","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-font","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-image","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-list","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-markdown-gfm","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-media-embed","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-paste-from-office","fixedVersion":"27.0.0"},{"ecosystem":"npm","name":"@ckeditor/ckeditor5-widget","fixedVersion":"27.0.0"}],"fix":null,"references":[{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-engine"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-font"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-image"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-list"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-media-embed"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-paste-from-office"},{"type":"WEB","url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-widget"},{"type":"ADVISORY","url":"https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-3rh3-wfr4-76mj"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21391"},{"type":"WEB","url":"https://github.com/ckeditor/ckeditor5/releases/tag/v27.0.0"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-engine"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-font"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-image"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-list"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-markdown-gfm"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-media-embed"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-paste-from-office"},{"type":"WEB","url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-widget"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T12:20:00.183386Z"}}