How severe is CVE-2021-33829?

CVE-2021-33829 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-33829?

CVE-2021-33829 affects the following packages: ckeditor4 (npm), drupal/core (Packagist), drupal/core (Packagist), drupal/core (Packagist), drupal/core (Packagist), drupal/drupal (Packagist), drupal/drupal (Packagist), drupal/drupal (Packagist), and 1 more. Ecosystems affected: npm, Packagist.

How do I fix CVE-2021-33829?

Update ckeditor4 to 4.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33829 is resolved across your whole dependency graph.

How do I detect CVE-2021-33829 in my npm, Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ckeditor4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-33829 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2021-33829 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-33829 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-33829?

CVE-2021-33829 has an EPSS (Exploit Prediction Scoring System) score of 3.2%, placing it in the 88th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-33829?

CVE-2021-33829 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2021-33829?

A Nuclei detection template exists for CVE-2021-33829, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-33829 published, and has it been updated?

CVE-2021-33829 was published on June 9, 2021 and was last updated on July 8, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm🐘 Packagist

Not in CISA KEV

MEDIUM severity

CVE-2021-33829 — ckeditor4

MEDIUM

CVE-2021-33829 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in ckeditor4. A fix is available for ckeditor4 — see the affected versions and patch details below.

ckeditor4 vulnerable to cross-site scripting

Also known asBIT-drupal-2021-33829DRUPAL-CORE-2021-003GHSA-rgx6-rjj4-c388

Published

Jun 9, 2021

Updated

Jul 8, 2026

Affected

9 pkgs

Patched

9 / 9

Exploits

None indexed

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

3.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs88th percentile — riskier than 88% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-33829 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

9 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

27other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

ckeditor4npm

56Kdownloads / week

Description

A cross-site scripting (XSS) vulnerability in the HTML Data Processor in CKEditor 4 4.14.0 through 4.16.x before 4.16.1 allows remote attackers to inject executable JavaScript code through a crafted comment because --!> is mishandled.

Affected Packages

9 total 9 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`ckeditor4`	≥ 4.14.0&&< 4.16.1	4.16.1`npm install ckeditor4@4.16.1`
🐘Packagist	`drupal/core`	≥ 7.0.0&&< 7.80	7.80`composer require drupal/core:^7.80`
🐘Packagist	`drupal/core`	≥ 8.0.0&&< 8.9.16	8.9.16`composer require drupal/core:^8.9.16`
🐘Packagist	`drupal/core`	≥ 9.0.0&&< 9.0.14	9.0.14`composer require drupal/core:^9.0.14`
🐘Packagist	`drupal/core`	≥ 9.1.0&&< 9.1.9	9.1.9`composer require drupal/core:^9.1.9`
🐘Packagist	`drupal/drupal`	≥ 7.0.0&&< 7.80	7.80`composer require drupal/drupal:^7.80`

Affected Products

4 products · 8 configurations

Application

ckeditorckeditor

≥ 4.14.0 && < 4.16.1

range

debian linuxdebian

1 version

9.0

Application

drupaldrupal

≥ 9.1.0 && < 9.1.9

range

fedorafedoraproject

3 versions

333435

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ckeditor4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ckeditor4 to 4.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33829 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

How to detect CVE-2021-33829

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-33829 -u https://target

Template: Drupal 7 CKEditor XSS
Severity: medium
Impact: Attackers can execute arbitrary JavaScript in the context of the victim's browser, leading to session hijacking or malicious actions.
Remediation: Update to version 4.16.1 or later.

Template by ProjectDiscovery nuclei-templates (0x_Akoko), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-33829 in your dependencies?

Find it across npm, Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

6.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

OpenSSF Scorecard

Package health score

security-advisories

4.8/10

Code-Review10/10

Maintained10/10

Branch-Protection0/10

Assessed Oct 5, 2026

Timeline

Disclosed

Jun 9, 2021

Last updated

Jul 8, 2026

Identifiers

CVE-2021-33829

GHSA-rgx6-rjj4-c388

BIT-drupal-2021-33829

DRUPAL-CORE-2021-003

References

Advisorylists.debian.org Advisorynvd.nist.gov Fixckeditor.com Fixdrupal.org Weblists.fedoraproject.org Weblists.fedoraproject.org Weblists.fedoraproject.org Webgithub.com Webgithub.com Weblists.fedoraproject.org Weblists.fedoraproject.org Weblists.fedoraproject.org Webnpmjs.com Packagegithub.com

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs affecting ckeditor4 are rated as high or higher (top: high).

CVE-2024-43411CVE-2024-43407CVE-2024-24815CVE-2024-24816CVE-2023-4771CVE-2020-27193CVE-2022-24728CVE-2021-41165

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 8, 2026