---
cve: "CVE-2021-21254"
severity: "MEDIUM"
cvss: 6.5
epss: "1.8%"
vendor: "ckeditor"
kev: false
exploited: false
published: "2021-01-29 21:55:14"
tags: [cve, security, medium]
source: tsecurity.de CVE-Dossier
exported: "2026-09-15T01:20:14+02:00"
---

# CVE-2021-21254

> 6.5 MEDIUM · 🧪 PoC

## Beschreibung

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

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Gering | warn |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Keine | good |
| I Integrität | Keine | good |
| A Verfügbarkeit | Hoch | bad |

## Patch verfügbar (OSV)

- 0139bbe2732c2e1fd0225d857639521436c790b4 (Commit)

## Referenzen

- <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>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2021-21254) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_