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NVD / CVE Program· CNA mitre

CVE-2021-33829: 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…

Noroxi assessment

Priority: Monitor (action score 25/100)

  • A ready-made attack module is public (Nuclei); exploiting it takes no special expertise.
  • Public proof-of-concept code exists (Exploit-DB / GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 3.1% (FIRST EPSS); higher than 88.1% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
  • Fixed version: ckeditor (Debian:12) 4.16.0+dfsg-2; ckeditor (Debian:9) 4.5.7+dfsg-2+deb9u1; ckeditor4 (npm) 4.16.1.

Low priority for now. Upgrade to ckeditor (Debian:12) 4.16.0+dfsg-2; ckeditor (Debian:9) 4.5.7+dfsg-2+deb9u1; ckeditor4 (npm) 4.16.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 6.1 · v3.1—Proof of concept Fix available
Published
Jun 9, 2021
Updated
Jun 16, 2026
EPSS
3.1% · 88th percentile

Report tools

JSON

Action score

25

Monitor

Low priority for now.

CVSS
24 / 40 · 6.1 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 3.1%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
ckeditorckeditor
fedoraprojectfedora
drupaldrupal
debiandebian linux

Is the CKEditor 4 on your site affected?

The free JavaScript library scanner reads the CKEditor 4 version from the files your site loads, matches this record and other known vulnerabilities, and gives the safe version on the same branch. If the version can't be read, it says so. No account needed.

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Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • ckeditor ckeditor4.14.0 and later · before 4.16.1
  • debian debian linux9.0
  • drupal drupal8.9.0 and later · before 8.9.16
  • drupal drupal9.0.0 and later · before 9.0.14
  • drupal drupal9.1.0 and later · before 9.1.9
  • fedoraproject fedora33
  • fedoraproject fedora34
  • fedoraproject fedora35

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12ckeditorbefore 4.16.0+dfsg-24.16.0+dfsg-2
Debian:12ckeditor3from 0—
Debian:9ckeditorbefore 4.5.7+dfsg-2+deb9u14.5.7+dfsg-2+deb9u1
npmckeditor4from 4.14.0 · before 4.16.14.16.1
Packagistdrupal/corefrom 7.0.0 · before 7.807.80
Packagistdrupal/corefrom 8.0.0 · before 8.9.168.9.16
Packagistdrupal/corefrom 9.0.0 · before 9.0.149.0.14
Packagistdrupal/corefrom 9.1.0 · before 9.1.99.1.9
Packagistdrupal/drupalfrom 7.0.0 · before 7.807.80
Packagistdrupal/drupalfrom 8.0.0 · before 8.9.168.9.16
Packagistdrupal/drupalfrom 9.0.0 · before 9.0.149.0.14
Packagistdrupal/drupalfrom 9.1.0 · before 9.1.99.1.9

Same product

ckeditor: all records

Other highest-scoring records for the same primary product.

  • CVE-2023-31541A unrestricted file upload vulnerability was discovered in the ‘Browse and upload images’ feature of the CKEditor v1.2.3 plugin for…
    39Monitor
  • CVE-2022-24729Regular expression Denial of Service in dialog plugin
    31Monitor
  • CVE-2011-4972hook_file_download in the CKEditor module 7.x-1.4 for Drupal does not properly restrict access to private files, which allows remote…
    31Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2021-26271Jan 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…
    27Monitor
  • ← EarlierCVE-2021-26272Jan 26, 2021 · It was possible to execute a ReDoS-type attack inside CKEditor 4 before 4.16 by persuading a victim to paste crafted URL-like text into the…
    27Monitor
  • Later →CVE-2021-32808Aug 12, 2021 · Cross-site scripting in ckeditor via abuse of undo functionality
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:ckeditor4.16.0+dfsg-2 · Debian:12Package registry (OSV)
npm:ckeditor44.16.1Package registry (OSV)
Packagist:drupal/core7.80Package registry (OSV)
Packagist:drupal/core8.9.16Package registry (OSV)
Packagist:drupal/core9.0.14Package registry (OSV)
Packagist:drupal/core9.1.9Package registry (OSV)
Packagist:drupal/drupal7.80Package registry (OSV)
Packagist:drupal/drupal8.9.16Package registry (OSV)
Packagist:drupal/drupal9.0.14Package registry (OSV)
Packagist:drupal/drupal9.1.9Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Nuclei detection template ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Nuclei detection templateNuclei template CVE-2021-33829 —

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • A user must open a link or visit a page.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
low · data can be read
Integrity
low · data or configuration can be modified
Availability
none

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality impact
Low
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSS vector

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

nvd-primary

Root cause

User content is inserted into the page as HTML. The browser interprets the content as code rather than data.

The bug in code

The whole CWE-79 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
commentEl.innerHTML = comment.body;

Fixed

ts
commentEl.textContent = comment.body;

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (5 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records