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 attackers to inject executable JavaScript code through a crafted comment because --!> is mishandled.

Published: 2021-06-09 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-33829 is rated Moderate Risk (49.6/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 3.19%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-33829

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 65.53% 3.19% -62.34%
2 2026-05-23 62.26% 65.53% +3.27%
3 2026-05-22 — 62.26% —

Full EPSS history (64 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33829

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-33829

GitHub Security Advisory for CVE-2021-33829

GHSA-rgx6-rjj4-c388 · Severity: medium · Ecosystem: npm — ckeditor4 vulnerable to cross-site scripting

OS Trackers for CVE-2021-33829

vendor priority summary link
debian not yet assigned CVE-2021-33829 not yet assigned priority: Debian including 2 source packages (ckeditor, ckeditor3), 4 status rows across 2 suites (bookworm, bullseye): open 2, resolved 2. https://security-tracker.debian.org/tracker/CVE-2021-33829
ubuntu medium CVE-2021-33829 medium priority: Ubuntu including 1 source packages (ckeditor), 9 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): released 4, ignored 2, not-affected 2, DNE 1. https://ubuntu.com/security/CVE-2021-33829

Affected software / configurations for CVE-2021-33829

Vendor Product Version Raw CPE
ckeditor ckeditor >= 4.14.0, < 4.16.1 cpe:2.3:a:ckeditor:ckeditor:*:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
drupal drupal >= 8.9.0, < 8.9.16 cpe:2.3:a:drupal:drupal:*:*:*:*:*:*:*:*
drupal drupal >= 9.0.0, < 9.0.14 cpe:2.3:a:drupal:drupal:*:*:*:*:*:*:*:*
drupal drupal >= 9.1.0, < 9.1.9 cpe:2.3:a:drupal:drupal:*:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

References for CVE-2021-33829

cvelogic Threat Intelligence