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CVE-2021-21254— Regular expression Denial of Service in Markdown plugin

Quick assessment

Affected
ckeditor ckeditor5
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

CKEditor是一套开源的、基于网页的文字编辑器。 CKEditor 5 存在资源管理错误漏洞，该漏洞允许滥用链接识别正则表达式，导致浏览器选项卡冻结。以下产品及版本受到影响：CKEditor 5 Markdown plugin at version <= 24.0.0。

CVSS 6.5 · Medium EPSS 1.79% · P77

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2021-21254

Vulnerability Information
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Vulnerability Title
Regular expression Denial of Service in Markdown plugin
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
CKEditor 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
CKEditor是一套开源的、基于网页的文字编辑器。 CKEditor 5 存在资源管理错误漏洞，该漏洞允许滥用链接识别正则表达式，导致浏览器选项卡冻结。以下产品及版本受到影响：CKEditor 5 Markdown plugin at version <= 24.0.0。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ckeditor ckeditor5 < 25.0.0 -

II. Public POCs for CVE-2021-21254

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III. Intelligence Information for CVE-2021-21254

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Vendor Advisories for CVE-2021-21254 (1)

Other References for CVE-2021-21254 (2)

IV. Related Vulnerabilities

Same product: ckeditor5
Same vendor: ckeditor
Same weakness: CWE-400

V. Comments for CVE-2021-21254

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