CVE-2021-33829: Ckeditor4 Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-rgx6-rjj4-c388
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CVSS 6.1
CWE-79
Published
Advisory Summary

CVE-2021-33829 is a MODERATE (CVSS 6.1) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Ckeditor4 libraries in the npm ecosystem. The issue involves ckeditor4 vulnerable to cross-site scripting. Remediation is available by upgrading affected packages to version 4.16.1, 7.80, 8.9.16, 9.0.14, 9.1.9.

CVE-2021-33829 at a Glance

CVE Identifier CVE-2021-33829
GHSA Identifier GHSA-rgx6-rjj4-c388
Severity MODERATE
CVSS v3.1 Base Score 6.1
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Ckeditor4
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 6.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2021-33829

To remediate this vulnerability, upgrade all affected Ckeditor4 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

ckeditor4 fixed: 4.16.1 
npm install ckeditor4@4.16.1
drupal/core fixed: 7.80 
Upgrade drupal/core to 7.80
drupal/core fixed: 8.9.16 
Upgrade drupal/core to 8.9.16
drupal/core fixed: 9.0.14 
Upgrade drupal/core to 9.0.14
drupal/core fixed: 9.1.9 
Upgrade drupal/core to 9.1.9
drupal/drupal fixed: 7.80 
Upgrade drupal/drupal to 7.80
drupal/drupal fixed: 8.9.16 
Upgrade drupal/drupal to 8.9.16
drupal/drupal fixed: 9.0.14 
Upgrade drupal/drupal to 9.0.14
drupal/drupal fixed: 9.1.9 
Upgrade drupal/drupal to 9.1.9
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls ckeditor4

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2021-33829, inspect your project dependencies using npm:

npm ls ckeditor4

Analyze the terminal output to locate any version of Ckeditor4 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.16.1), your application is affected.

Note: The npm ls ckeditor4 command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Ckeditor4, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2021-33829 Affected Ckeditor4 Versions

9 component(s)
Fixed Versions:
4.16.17.808.9.169.0.149.1.9
Product / Package Ecosystem Affected Versions Fixed Version
ckeditor4
npm/ckeditor4
npm
≥ 4.14.0
< 4.16.1
4.16.1
drupal/core
 Packagist
≥ 7.0.0
< 7.80
7.80
drupal/core
 Packagist
≥ 8.0.0
< 8.9.16
8.9.16
drupal/core
 Packagist
≥ 9.0.0
< 9.0.14
9.0.14
drupal/core
 Packagist
≥ 9.1.0
< 9.1.9
9.1.9
drupal/drupal
 Packagist
≥ 7.0.0
< 7.80
7.80
drupal/drupal
 Packagist
≥ 8.0.0
< 8.9.16
8.9.16
drupal/drupal
 Packagist
≥ 9.0.0
< 9.0.14
9.0.14
drupal/drupal
 Packagist
≥ 9.1.0
< 9.1.9
9.1.9

References

NVD — CVE-2021-33829 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-33829
ckeditor.com/blog/ckeditor-4.16.... WEB
https://ckeditor.com/blog/ckeditor-4.16.1-with-accessibility-enhancements/#improvements-for-comments-in-html-parser
Ckeditor4 Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/core/CVE-2021-33829.yaml
Ckeditor4 Source Repository REPOSITORY
https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/drupal/CVE-2021-33829.yaml
Ckeditor4 Source Repository REPOSITORY
https://github.com/ckeditor/ckeditor4
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2021/11/msg00007.html
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NYA354LJP47KCVJMTUO77ZCX3ZK42G3T
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UVOYN2WKDPLKCNILIGEZM236ABQASLGW
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAGNWHFIQAVCP537KFFS2A2GDG66J7XD
www.drupal.org/sa-core-2021-003 WEB
https://www.drupal.org/sa-core-2021-003
www.npmjs.com/package/ckeditor4 WEB
https://www.npmjs.com/package/ckeditor4

Frequently Asked Questions

What is CVE-2021-33829?
CVE-2021-33829 is a security vulnerability in Ckeditor4 involving ckeditor4 vulnerable to cross-site scripting under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Ckeditor4 versions are affected?
Affected versions include releases prior to 4.16.1, 7.80, 8.9.16, 9.0.14, 9.1.9 across affected packages: ckeditor4, drupal/core, drupal/drupal.
What version fixes CVE-2021-33829?
Upgrading to 4.16.1, 7.80, 8.9.16, 9.0.14, 9.1.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is ckeditor4 affected?
Yes, ckeditor4 is affected in releases prior to 4.16.1. Upgrade your dependency to 4.16.1 or later.
Is drupal/core affected?
Yes, drupal/core is affected in releases prior to 7.80, 8.9.16, 9.0.14, 9.1.9. Upgrade your dependency to 7.80, 8.9.16, 9.0.14, 9.1.9 or later.
What is the CVSS score of CVE-2021-33829?
CVE-2021-33829 has a CVSS v3.1 base score of 6.1 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
What CWE is associated with CVE-2021-33829?
CVE-2021-33829 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check npm dependencies for CVE-2021-33829?
Run the dependency tree command: 'npm ls ckeditor4'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-rgx6-rjj4-c388",
  "modified" : "2024-02-08T09:40:35Z",
  "published" : "2021-06-21T17:16:42Z",
  "aliases" : [ "CVE-2021-33829" ],
  "summary" : "ckeditor4 vulnerable to cross-site scripting",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
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      "name" : "ckeditor4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.14.0"
      }, {
        "fixed" : "4.16.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
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        "introduced" : "7.0.0"
      }, {
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      } ]
    } ]
  }, {
    "package" : {
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      "name" : "drupal/core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.9.16"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
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      } ]
    } ]
  }, {
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      "ecosystem" : "Packagist",
      "name" : "drupal/core"
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    "ranges" : [ {
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    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/drupal"
    },
    "ranges" : [ {
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      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/drupal"
    },
    "ranges" : [ {
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      "events" : [ {
        "introduced" : "8.0.0"
      }, {
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      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/drupal"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "9.0.0"
      }, {
        "fixed" : "9.0.14"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "drupal/drupal"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "9.1.0"
      }, {
        "fixed" : "9.1.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-33829"
  }, {
    "type" : "WEB",
    "url" : "https://ckeditor.com/blog/ckeditor-4.16.1-with-accessibility-enhancements/#improvements-for-comments-in-html-parser"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/core/CVE-2021-33829.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/FriendsOfPHP/security-advisories/blob/master/drupal/drupal/CVE-2021-33829.yaml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ckeditor/ckeditor4"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2021/11/msg00007.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NYA354LJP47KCVJMTUO77ZCX3ZK42G3T"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/UVOYN2WKDPLKCNILIGEZM236ABQASLGW"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WAGNWHFIQAVCP537KFFS2A2GDG66J7XD"
  }, {
    "type" : "WEB",
    "url" : "https://www.drupal.org/sa-core-2021-003"
  }, {
    "type" : "WEB",
    "url" : "https://www.npmjs.com/package/ckeditor4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-06-14T17:22:32Z",
    "nvd_published_at" : "2021-06-09T12:15:00Z"
  }
}