{"id":"CVE-2021-21391","aliases":["EUVD-2021-0749","GHSA-3rh3-wfr4-76mj","UBUNTU-CVE-2021-21391"],"status":"published","title":"Regular expression Denial of Service in multiple 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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","severity":{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.01667,"percentile":0.7695,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-400"],"published":"2021-04-06T17:28:41Z","modified":"2026-10-20T10:53:49Z","fixes":[{"ecosystem":"npm","package":"@ckeditor/ckeditor5-engine","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-font","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-image","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-list","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-markdown-gfm","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-media-embed","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-paste-from-office","fixed_in":["27.0.0"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@ckeditor/ckeditor5-widget","fixed_in":["27.0.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-engine","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-font","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-image","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-list","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-markdown-gfm","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-media-embed","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-paste-from-office","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@ckeditor/ckeditor5-widget","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"26.0.0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-engine","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-font","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-image","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-list","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-markdown-gfm","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-media-embed","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-paste-from-office","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"npm","package":"@ckeditor/ckeditor5-widget","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"27.0.0"}]}]},{"source":"osv","ecosystem":"Ubuntu:18.04:LTS","package":"ckeditor3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.6.1+dfsg-1"]},{"source":"osv","ecosystem":"Ubuntu:20.04:LTS","package":"ckeditor3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.6.1+dfsg-3","3.6.6.1+dfsg-4"]},{"source":"osv","ecosystem":"Ubuntu:22.04:LTS","package":"ckeditor3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.6.1+dfsg-7"]},{"source":"osv","ecosystem":"Ubuntu:24.04:LTS","package":"ckeditor3","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["3.6.6.1+dfsg-7"]}],"products":[{"vendor":"ckeditor","product":"ckeditor5"},{"vendor":"ckeditor","product":"ckeditor5-engine"},{"vendor":"ckeditor","product":"ckeditor5-font"},{"vendor":"ckeditor","product":"ckeditor5-image"},{"vendor":"ckeditor","product":"ckeditor5-list"},{"vendor":"ckeditor","product":"ckeditor5-markdown-gfm"},{"vendor":"ckeditor","product":"ckeditor5-media-embed"},{"vendor":"ckeditor","product":"ckeditor5-paste-from-office"},{"vendor":"ckeditor","product":"ckeditor5-widget"}],"references":[{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-3rh3-wfr4-76mj","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web","report"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-engine","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-font","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-image","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-list","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-media-embed","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-paste-from-office","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://www.npmjs.com/package/%40ckeditor/ckeditor5-widget","tags":["x_refsource_MISC","x_transferred","web"]},{"url":"https://github.com/ckeditor/ckeditor5/releases/tag/v27.0.0","tags":["web"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-engine","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-font","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-image","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-list","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-markdown-gfm","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-media-embed","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-paste-from-office","tags":["web","report"]},{"url":"https://www.npmjs.com/package/@ckeditor/ckeditor5-widget","tags":["web","report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21391","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-3rh3-wfr4-76mj"},{"url":"https://ubuntu.com/security/CVE-2021-21391","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-21391","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-21391","title":"Regular expression Denial of Service in multiple 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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","status":"published","published":"2021-04-29T00:20:19Z","modified":"2024-08-03T18:09:15.938Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"cna"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:33:00.137099Z"}],"euvd":[{"id":"EUVD-2021-0749","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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","status":"published","published":"2021-04-29T00:20:19Z","modified":"2024-08-03T18:09:15Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-03T03:25:06.913643Z"}],"ghsa":[{"id":"GHSA-3rh3-wfr4-76mj","title":"Regular expression Denial of Service in multiple packages","description":"\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.","status":"published","published":"2021-04-06T17:28:41Z","modified":"2023-02-01T05:05:16Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:36:33.613868Z"}],"nvd":[{"id":"CVE-2021-21391","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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","status":"published","published":"2021-04-29T01:15:07.883Z","modified":"2026-06-17T03:35:28.5Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"secondary"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium","assessor":"primary"},{"version":"2.0","score":4.3,"vector":"AV:N/AC:M/Au:N/C:N/I:N/A:P","level":"medium","assessor":"primary"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:06:52.81233Z"}],"osv":[{"id":"CVE-2021-21391","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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","status":"published","published":"2021-04-29T01:15:07.883Z","modified":"2026-10-20T10:53:49.937711153Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-02T15:44:18.004149Z"},{"id":"GHSA-3rh3-wfr4-76mj","title":"Regular expression Denial of Service in multiple packages","description":"\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.","status":"published","published":"2021-04-06T17:28:41Z","modified":"2026-07-08T06:27:26.938294321Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T15:46:36.092962Z"},{"id":"UBUNTU-CVE-2021-21391","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 \u003c= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.","status":"published","published":"2021-04-29T01:15:00Z","modified":"2026-01-20T17:21:31.493249Z","cvss":[{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H","level":"medium"}],"updated_at":"2026-11-02T15:54:26.29421Z"}]}}