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CVE-2021-33829: A cross-site scripting (XSS) vulnerability in the HTML Data Processor in CKEditor 4 4.14.0 through 4.16.x b...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CKEditor 4 could mishandle a crafted HTML comment and allow JavaScript to run where edited content is displayed. This is a browser-side risk: attackers may target users who view or edit affected content, with impact depending on session privileges and where CKEditor is exposed.

Executive priority

Treat as a focused patching priority for CMS, admin, and customer-facing editing workflows. It is not cited as actively exploited in the bundle, but XSS in privileged content paths can create meaningful business risk.

Technical view

CVE-2021-33829 affects CKEditor 4 versions 4.14.0 through 4.16.x before 4.16.1. The HTML Data Processor mishandles a crafted comment terminator, enabling cross-site scripting. The bundle cites CKEditor 4.16.1 and downstream Drupal, Fedora, and Debian security advisories.

Likely exposure

Organizations are most likely exposed through applications bundling CKEditor 4 in content editing, CMS, admin, or rich-text workflows. Exposure is higher where untrusted or lower-privileged users can submit HTML content later viewed by privileged users.

Exploitation context

The supplied bundle does not show CISA KEV listing or any cited active exploitation claim. The vulnerability is remotely triggerable as XSS, but successful impact depends on affected CKEditor versions and whether crafted content reaches a victim browser.

Researcher notes

Evidence is strongest for CKEditor 4 version range and the HTML comment parsing flaw. The bundle does not provide CVSS, exploit telemetry, or detailed downstream affected version ranges, so validate each packaged dependency against its vendor advisory.

Mitigation direction

  • Upgrade CKEditor 4 to 4.16.1 or later where directly managed.
  • Apply relevant Drupal, Fedora, or Debian security updates where CKEditor is packaged downstream.
  • Check vendor guidance for bundled CKEditor in CMS or application dependencies.
  • Restrict untrusted HTML submission until affected instances are updated.
  • Review content sanitization controls around rich-text input and rendering.

Validation and detection

  • Inventory applications and packages using CKEditor 4.
  • Confirm whether versions fall between 4.14.0 and before 4.16.1.
  • Check CMS and OS package advisories for applied security updates.
  • Review public routes where untrusted users can create rich-text content.
  • Verify admin or privileged users are not exposed to unsanitized submitted content.
Prepared
Confidence
high
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
7Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.