How severe is CVE-2026-28343?

CVE-2026-28343 has a CVSS score of 6.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-28343?

CVE-2026-28343 affects the following packages: @ckeditor/ckeditor5-html-support (npm), ckeditor5 (npm). Ecosystems affected: npm.

How do I fix CVE-2026-28343?

Update @ckeditor/ckeditor5-html-support to 47.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28343 is resolved across your whole dependency graph.

How do I detect CVE-2026-28343 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @ckeditor/ckeditor5-html-support, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-28343 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-28343 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-28343 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-28343?

CVE-2026-28343 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 25th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-28343?

CVE-2026-28343 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-28343 published, and has it been updated?

CVE-2026-28343 was published on March 5, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

CVE-2026-28343 — @ckeditor/ckeditor5-html-…

MEDIUM

CVE-2026-28343 is a medium-severity (CVSS 6.4) Cross-site Scripting (XSS) vulnerability in @ckeditor/ckeditor5-html-support. A fix is available for @ckeditor/ckeditor5-html-support — see the affected versions and patch details below.

CKEditor: Cross-site scripting (XSS) in the HTML Support package

Also known asGHSA-jrqm-vmqc-gm93

Published

Mar 5, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-28343.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs25th percentile — riskier than 25% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

293other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@ckeditor/ckeditor5-html-supportnpm

1000Kdownloads / week

ckeditor5npm

1.3Mdownloads / week

Description

Impact

A 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.

This vulnerability affects only installations where the editor configuration meets the following criteria:

General HTML Support is enabled,
General HTML Support configuration allows inserting unsafe markup (see Security section to learn more).

Patches

The problem has been recognized and patched. The fix will be available in version 47.6.0 (and above).

Workarounds

CKEditor 5 recommends configuring General HTML Support securely to ensure that unsafe content is not accepted. Please refer to the Security section for detailed guidance.

Credits

CKEditor 5 would like to thank:

Emilio Kevin
Jeongwoo Lee, Younsoung Kim, Minseok Kim and Jinyeong Kim from ENKI Whitehat

for responsibly reporting this vulnerability.

For more information

Email us at [email protected] if you have any questions or comments about this advisory.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@ckeditor/ckeditor5-html-support`	≥ 29.0.0&&< 47.6.0	47.6.0`npm install @ckeditor/ckeditor5-html-support@47.6.0`
📦npm	`ckeditor5`	≥ 29.0.0&&< 47.6.0	47.6.0`npm install ckeditor5@47.6.0`

Affected Products

1 product · 1 configurations

Application

ckeditor5ckeditor

< 47.6.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @ckeditor/ckeditor5-html-support, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @ckeditor/ckeditor5-html-support to 47.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28343 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### Impact A 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. This vulnerability affects only installations where the editor configuration meets the following criteria: * [General HTML Support](https://ckeditor.com/docs/ckeditor5/latest/features/html/general-html-support.html) is enabled, * General HTML Support configuration allows inserting uns

O3 Security · Impact-Aware SCA

Is CVE-2026-28343 in your dependencies?

Find it across npm, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

6.4/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

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

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

ckeditor5

4.6/10

Code-Review0/10

Maintained10/10

Branch-Protection1/10

Assessed Nov 2, 2026

Timeline

Disclosed

Mar 5, 2026

Last updated

Oct 28, 2026

Identifiers

CVE-2026-28343

GHSA-jrqm-vmqc-gm93

References

Advisorygithub.com · CVE 2026 28343.json Advisorygithub.com · GHSA jrqm vmqc gm93 Advisorynvd.nist.gov · CVE 2026 28343 Webgithub.com · v29.0.0 Webgithub.com · v47.6.0 Packagegithub.com · ckeditor5

Related vulnerabilities

Also affects @ckeditor/ckeditor5-html-support

This CVE is medium severity, in line with the other 1 CVE affecting @ckeditor/ckeditor5-html-support.

CVE-2022-31175

Also affects ckeditor5

This CVE is medium severity; 2 of 4 other CVEs affecting ckeditor5 are rated as high or higher (top: high).

CVE-2026-116688CVE-2026-116687CVE-2025-58064CVE-2024-45613

Same weakness: CWE-79

This CVE is medium severity; 3 of 3 other CVEs with CWE-79 are rated as high or higher (top: critical).

CVE-2026-55649CVE-2026-113787CVE-2026-44267Browse all CWE-79

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 28, 2026

CVE-2026-28343 — @ckeditor/ckeditor5-html-…

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Impact

Patches

Workarounds

Credits

For more information

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2026-28343 in your dependencies?