CVE-2026-28343: @ckeditor/ckeditor5 html support Cross-Site Scripting Vulnerability
MODERATECVE-2026-28343 is a MODERATE (CVSS 6.4) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting @ckeditor/ckeditor5 html support libraries in the npm ecosystem. The issue involves ckeditor 5 has cross-site scripting (xss) in the html support package. Remediation is available by upgrading affected packages to version 47.6.0.
CVE-2026-28343 at a Glance
Security Impact
CVSS: 6.4
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N).
How to Fix CVE-2026-28343
To remediate this vulnerability, upgrade all affected @ckeditor/ckeditor5 html support dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install @ckeditor/ckeditor5-html-support@47.6.0npm install ckeditor5@47.6.0Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls @ckeditor/ckeditor5-html-supportHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-28343, inspect your project dependencies using npm:
npm ls @ckeditor/ckeditor5-html-supportAnalyze the terminal output to locate any version of @ckeditor/ckeditor5 html support in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 47.6.0), your application is affected.
Note: The npm ls @ckeditor/ckeditor5-html-support 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 @ckeditor/ckeditor5 html support, 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
CVE-2026-28343 Affected @ckeditor/ckeditor5 html support Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
@ckeditor/ckeditor5-html-support
|
npm |
≥ 29.0.0
< 47.6.0
|
47.6.0
|
|
ckeditor5
|
npm |
≥ 29.0.0
< 47.6.0
|
47.6.0
|
References
Frequently Asked Questions
What is CVE-2026-28343?
Which @ckeditor/ckeditor5 html support versions are affected?
What version fixes CVE-2026-28343?
Is @ckeditor/ckeditor5-html-support affected?
Is ckeditor5 affected?
What is the CVSS score of CVE-2026-28343?
What CWE is associated with CVE-2026-28343?
How can I check npm dependencies for CVE-2026-28343?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-jrqm-vmqc-gm93",
"modified" : "2026-03-19T18:45:07Z",
"published" : "2026-03-04T18:49:32Z",
"aliases" : [ "CVE-2026-28343" ],
"summary" : "CKEditor 5 has Cross-site Scripting (XSS) in the HTML Support package",
"details" : "### Impact\nA Cross-Site Scripting (XSS) vulnerability has been discovered in the General HTML Support feature. This vulnerability could be triggered by inserting specially crafted markup, leading to unauthorized JavaScript code execution, if the editor instance used an unsafe General HTML Support configuration.\n\nThis vulnerability affects only installations where the editor configuration meets the following criteria:\n\n* [General HTML Support](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html) is enabled,\n* General HTML Support configuration allows inserting unsafe markup (see [Security](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html#security) section to learn more).\n\n### Patches\nThe problem has been recognized and patched. The fix will be available in version 47.6.0 (and above).\n\n### Workarounds\nCKEditor 5 recommends configuring General HTML Support securely to ensure that unsafe content is not accepted. Please refer to the [Security](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html#security) section for detailed guidance.\n\n### Credits\nCKEditor 5 would like to thank: \n- Emilio Kevin\n- Jeongwoo Lee, Younsoung Kim, Minseok Kim and Jinyeong Kim from ENKI Whitehat\n\nfor responsibly reporting this vulnerability.\n\n### For more information\nEmail us at [security@cksource.com](mailto:security@cksource.com) if you have any questions or comments about this advisory.",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "@ckeditor/ckeditor5-html-support"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "29.0.0"
}, {
"fixed" : "47.6.0"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "ckeditor5"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "29.0.0"
}, {
"fixed" : "47.6.0"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-jrqm-vmqc-gm93"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-28343"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/ckeditor/ckeditor5"
}, {
"type" : "WEB",
"url" : "https://github.com/ckeditor/ckeditor5/releases/tag/v29.0.0"
}, {
"type" : "WEB",
"url" : "https://github.com/ckeditor/ckeditor5/releases/tag/v47.6.0"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-79" ],
"severity" : "MODERATE",
"github_reviewed" : true,
"github_reviewed_at" : "2026-03-04T18:49:32Z",
"nvd_published_at" : "2026-03-05T20:16:16Z"
}
}