{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "cpe": "cpe:2.3:a:ckeditor:ckeditor5:*:*:*:*:*:*:*:*",
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "25.0.0"
              }
            ],
            "source": [
              "CPE_RANGE",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0139bbe2732c2e1fd0225d857639521436c790b4"
            }
          ],
          "repo": "https://github.com/ckeditor/ckeditor5",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-hgmg-hhc8-g5wr"
  ],
  "database_specific": {},
  "details": "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 \u003c= 24.0.0. The problem has been recognized and patched. The fix will be available in version 25.0.0.",
  "id": "CVE-2021-21254",
  "modified": "2026-07-08T05:38:47.579194858Z",
  "published": "2021-01-29T22:15:14.797Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}