{"id":"GHSA-3rh3-wfr4-76mj","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 \u003c= 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.","aliases":["CVE-2021-21391"],"modified":"2026-07-08T06:27:26.938294321Z","published":"2021-04-06T17:28:41Z","database_specific":{"severity":"MODERATE","cwe_ids":["CWE-400"],"github_reviewed_at":"2021-03-31T18:37:46Z","github_reviewed":true,"nvd_published_at":"2021-04-29T01:15:00Z"},"references":[{"type":"WEB","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"}],"affected":[{"package":{"name":"@ckeditor/ckeditor5-engine","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-engine"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json","last_known_affected_version_range":"\u003c= 26.0.0"}},{"package":{"name":"@ckeditor/ckeditor5-font","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-font"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json","last_known_affected_version_range":"\u003c= 26.0.0"}},{"package":{"name":"@ckeditor/ckeditor5-image","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-image"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 26.0.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json"}},{"package":{"name":"@ckeditor/ckeditor5-list","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-list"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json","last_known_affected_version_range":"\u003c= 26.0.0"}},{"package":{"name":"@ckeditor/ckeditor5-markdown-gfm","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-markdown-gfm"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json","last_known_affected_version_range":"\u003c= 26.0.0"}},{"package":{"name":"@ckeditor/ckeditor5-media-embed","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-media-embed"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 26.0.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json"}},{"package":{"name":"@ckeditor/ckeditor5-paste-from-office","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-paste-from-office"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 26.0.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json"}},{"package":{"name":"@ckeditor/ckeditor5-widget","ecosystem":"npm","purl":"pkg:npm/%40ckeditor/ckeditor5-widget"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 26.0.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/04/GHSA-3rh3-wfr4-76mj/GHSA-3rh3-wfr4-76mj.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H"}]}