CVE-2021-21391

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 1.7%, top 26% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 2%CVSS: 6.5Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
6.5
EG Score
6.5(medium)
EG Risk
34(Track)
EG Risk 34/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation2% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
74.3%
KEV
Not listed

Published

April 29, 2021

Last Modified

November 21, 2024

References (18)

Affected Packages

(8 across 1 ecosystem)
npm(8)
PackageVulnerable rangeFixed inDependents
@ckeditor/ckeditor5-engine—27.0.0—
@ckeditor/ckeditor5-font—27.0.0—
@ckeditor/ckeditor5-image—27.0.0—
@ckeditor/ckeditor5-list—27.0.0—
@ckeditor/ckeditor5-markdown-gfm—27.0.0—
@ckeditor/ckeditor5-media-embed—27.0.0—
@ckeditor/ckeditor5-paste-from-office—27.0.0—
@ckeditor/ckeditor5-widget—27.0.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 49× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 102 total refreshes for this CVE.

  1. 2026-07-23 01:57 UTCEG score recompute
  2. 2026-07-22 22:43 UTCEG score recompute
  3. 2026-07-22 14:05 UTCEPSS rescore
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  40. 2026-06-13 07:13 UTCOSV refresh
  41. 2026-06-12 23:10 UTCEPSS rescore
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  72. 2026-05-26 17:18 UTCEG score recompute
  73. 2026-05-26 13:42 UTCEPSS rescore
  74. 2026-05-26 13:42 UTCEPSS rescore
  75. 2026-05-26 07:17 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-21391?
CVE-2021-21391 is a medium vulnerability published on April 29, 2021. 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…
When was CVE-2021-21391 disclosed?
CVE-2021-21391 was first published in the National Vulnerability Database on April 29, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21391 actively exploited?
CVE-2021-21391 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 74.3% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-21391?
CVE-2021-21391 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2021-21391?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21391, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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