Provide references for CVE-2021-21254.
Where can I find more information about CVE-2021-21254?
References are available at: https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr, https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0, https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm.