CVE-2021-26271

MEDIUMNVD 6.56.5—

6.5

It was possible to execute a ReDoS-type attack inside CKEditor 4 before 4.16 by persuading a victim to paste crafted text into the Styles input of specific dialogs (in the Advanced Tab for Dialogs plugin).

CVSS v3: 6.5
EG Score: 6.5(medium)
EPSS: 70.2%
KEV: Not listed

Published

January 26, 2021

Last Modified

November 21, 2024

References (8)

cve@mitrehttps://ckeditor.com/blog/CKEditor-4.16-with-improved-image-pasting-High-Contrast-support-and-a-new-color-API/#security-comes-first
cve@mitrehttps://github.com/ckeditor/ckeditor4/blob/major/CHANGES.md#ckeditor-416
cve@mitrehttps://www.oracle.com//security-alerts/cpujul2021.html
cve@mitrehttps://www.oracle.com/security-alerts/cpuoct2021.html
af854a3a-2127-422b-91ae-364da2661108https://ckeditor.com/blog/CKEditor-4.16-with-improved-image-pasting-High-Contrast-support-and-a-new-color-API/#security-comes-first
af854a3a-2127-422b-91ae-364da2661108https://github.com/ckeditor/ckeditor4/blob/major/CHANGES.md#ckeditor-416
af854a3a-2127-422b-91ae-364da2661108https://www.oracle.com//security-alerts/cpujul2021.html
af854a3a-2127-422b-91ae-364da2661108https://www.oracle.com/security-alerts/cpuoct2021.html

Affected Packages

(1 across 1 ecosystem)

npm(1)

Package	Vulnerable range	Fixed in	Dependents
ckeditor4-dev	—	4.16	—

Weakness Classification(1)

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

CWE-829Inclusion of Functionality from Untrusted Control Sphere

Data Freshness Timeline

(refreshed 6× in last 7d / 6× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-05-27 13:39 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-26 21:36 UTCEG score recompute
2026-05-26 13:42 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch

Frequently asked(5)

What is CVE-2021-26271?

CVE-2021-26271 is a medium vulnerability published on January 26, 2021. It was possible to execute a ReDoS-type attack inside CKEditor 4 before 4.16 by persuading a victim to paste crafted text into the Styles input of specific dialogs (in the Advanced Tab for Dialogs plugin).

When was CVE-2021-26271 disclosed?

CVE-2021-26271 was first published in the National Vulnerability Database on January 26, 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-2021-26271 actively exploited?

CVE-2021-26271 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 70.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-26271?

CVE-2021-26271 has a CVSS v3 base score of 6.5 (NVD).

How do I remediate CVE-2021-26271?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26271, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-26271

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