CVE-2021-21391

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 <= 26.0.0. The
problem has been recognized and patched. The fix will be available in
version 27.0.0.

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