{"cve":"CVE-2021-21254","nvd":{"published":"2021-01-29T22:15:14.797","modified":"2026-06-17T03:35:08.190","status":"Modified","description":"CKEditor 5 is an open source rich text editor framework with a modular architecture. The CKEditor 5 Markdown plugin (@ckeditor/ckeditor5-markdown-gfm) before version 25.0.0 has a regex denial of service (ReDoS) vulnerability. The vulnerability allowed to abuse link recognition regular expression, which could cause a significant performance drop resulting in browser tab freeze. It affects all users using CKEditor 5 Markdown plugin at version <= 24.0.0. The problem has been recognized and patched. The fix will be available in version 25.0.0.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":6.5},"cwes":["CWE-400"],"references":["https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0","https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr","https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm","https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0","https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr"],"products":["ckeditor:ckeditor5"],"source":"nvd","synced_at":"2026-10-19T21:14:10.479542811+00:00"},"epss":{"cve":"CVE-2021-21254","score":0.01814,"percentile":0.78665,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-hgmg-hhc8-g5wr","url":"https://osv.dev/vulnerability/GHSA-hgmg-hhc8-g5wr","summary":"CKEditor 5 Markdown plugin Regular expression Denial of Service","modified":"2026-07-08T06:29:35.375771949Z","packages":[{"ecosystem":"npm","name":"@ckeditor/ckeditor5-markdown-gfm","purl":"pkg:npm/%40ckeditor/ckeditor5-markdown-gfm","ranges":["<25.0.0"],"fixed":["25.0.0"]}]}],"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."]}