CVE-2026-28343 in CKeditor5
Summary
by MITRE • 03/05/2026
CKEditor 5 is a modern JavaScript rich-text editor with an MVC architecture. Starting in version 29.0.0 and prior to version 47.6.0, 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 issue has been patched in version 47.6.0.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 03/19/2026
The vulnerability identified as CVE-2026-28343 affects CKEditor 5, a widely-used JavaScript rich-text editor that employs an MVC architecture for content management. This particular flaw resides within the General HTML Support feature, which allows developers to define which HTML elements and attributes are permitted within the editor environment. The vulnerability exists in versions starting from 29.0.0 up to but not including 47.6.0, representing a significant portion of the editor's development cycle where users were exposed to potential security risks.
The technical flaw manifests through a cross-site scripting vulnerability that can be exploited when the editor processes specially crafted markup. This occurs when an editor instance is configured with an unsafe General HTML Support configuration that fails to properly sanitize or validate incoming HTML content. The vulnerability stems from inadequate input validation and sanitization mechanisms within the HTML support feature, allowing malicious actors to inject JavaScript code that executes within the context of the victim's browser. This represents a classic XSS vulnerability that operates under CWE-79, which specifically addresses cross-site scripting flaws in web applications.
The operational impact of this vulnerability is substantial as it enables unauthorized JavaScript code execution, potentially allowing attackers to perform actions such as stealing user sessions, defacing content, redirecting users to malicious sites, or extracting sensitive information from the victim's browser environment. The risk is particularly elevated when the editor is used in web applications where users can input content, as the vulnerability can be triggered through seemingly benign HTML markup that contains malicious payloads. This issue affects not only the integrity of content but also the confidentiality and availability of web applications that rely on CKEditor 5 for rich-text editing capabilities.
Mitigation strategies should prioritize upgrading to CKEditor 5 version 47.6.0 or later, which contains the necessary patches to address the XSS vulnerability. Organizations should also review their existing General HTML Support configurations to ensure they implement proper input sanitization and validation measures. Security best practices recommend implementing Content Security Policy headers, using a whitelist approach for allowed HTML elements, and regularly auditing editor configurations to prevent similar vulnerabilities. The remediation process should include comprehensive testing of the updated editor environment to verify that the vulnerability has been properly addressed and that existing functionality remains intact. This vulnerability highlights the importance of maintaining up-to-date software components and implementing robust security measures within rich-text editing environments, particularly in applications where user-generated content is processed and displayed.