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CVE-2021-21254

CVE-2021-21254: CKEditor 5 Markdown plugin Regular expression Denial of Service

6.5

CVSS Score
3.1

Basic Information

CVE ID
CVE-2021-21254
GHSA ID
GHSA-hgmg-hhc8-g5wr
EPSS Score
0.58024%
CWE
CWE-400
Published
1/29/2021
Updated
1/30/2023
KEV Status
No
Technology
TechnologyJavaScript

Technical Details

CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Package NameEcosystemVulnerable VersionsFirst Patched Version
@ckeditor/ckeditor5-markdown-gfmnpm<= 24.0.025.0.0

Vulnerability Intelligence
Miggo AIMiggo AI

Miggo AIRoot Cause Analysis

The vulnerability explicitly relates to a ReDoS in link recognition regex in the Markdown plugin. While exact function names aren't provided in the advisory, CKEditor's architecture uses GFMDataProcessor for Markdown conversion. The _htmlToMarkdown method (or similar link handling logic) would contain the vulnerable regex pattern matching links. The high confidence comes from: 1) The advisory specifically mentions 'link recognition regular expression' 2) The patched version 25.0.0 would logically modify this processing logic 3) ReDoS vulnerabilities in Markdown processors are typically found in the regex patterns used for link/URL detection.

Vulnerable functions

Only Mi**o us*rs **n s** t*is s**tion

WAF Protection Rules

WAF Rule

### Imp**t * r**ul*r *xpr*ssion **ni*l o* s*rvi** (R**oS) vuln*r**ility **s ***n *is*ov*r** in t** *K**itor * M*rk*own plu*in *o**. T** vuln*r**ility *llow** to **us* * link r**o*nition r**ul*r *xpr*ssion, w*i** *oul* **us* * si*ni*i**nt p*r*orm*n**

Reasoning

T** vuln*r**ility *xpli*itly r*l*t*s to * R**oS in link r**o*nition r***x in t** M*rk*own plu*in. W*il* *x**t *un*tion n*m*s *r*n't provi*** in t** **visory, `*K**itor`'s *r**it**tur* us*s `**M**t*Pro**ssor` *or M*rk*own *onv*rsion. T** `_*tmlToM*rk*