CVE-2026-59167: SunEditor WYSIWYG XSS Vulnerability

CVE-2026-59167 Overview

CVE-2026-59167 is a stored cross-site scripting (XSS) vulnerability in SunEditor, a lightweight vanilla JavaScript WYSIWYG editor. The sanitizer in src/lib/core.js fails to consistently reject namespaced or custom HTML elements. This gap allows event-handler attributes to remain on crafted elements. When an application renders attacker-controlled editor content, user interaction triggers the retained handler and executes script in the application's browser origin. The flaw is tracked as [CWE-79] and is fixed in SunEditor version 2.47.11.

Critical Impact
Attackers can achieve stored XSS in any application that renders SunEditor output, leading to session theft, data exposure, and unauthorized browser-context actions on behalf of the victim.

Affected Products

SunEditor versions prior to 2.47.11
Web applications embedding SunEditor for rich-text input
Downstream frameworks and CMS integrations bundling vulnerable SunEditor builds

Discovery Timeline

2026-09-23 - CVE-2026-59167 published to NVD
2026-09-23 - Last updated in NVD database

Technical Details for CVE-2026-59167

Vulnerability Analysis

SunEditor sanitizes user-supplied HTML before rendering it back to the DOM. The sanitizer strips known dangerous elements and attributes but does not consistently walk namespaced elements (for example, elements with a colon-prefixed tag name) or arbitrary custom elements. Because the tag filter fails to match these shapes, attached event-handler attributes such as onclick, onmouseover, or onerror survive the sanitization pass. When the host application renders the resulting markup, the browser attaches the handlers as normal DOM listeners. A user interaction, such as hovering, clicking, or an image load event, causes the JavaScript payload to execute inside the application origin.

Root Cause

The root cause is incomplete input validation inside the _setCodeDataToEditor code path in src/lib/core.js. Before the patch, the function passed the raw code view directly into the HTML parser. The disallowed-tag filter was never invoked on that content, so crafted namespaced or custom elements bypassed the sanitizer while retaining their event-handler attributes.

Attack Vector

An attacker submits crafted HTML through any surface that stores or forwards SunEditor content, such as comments, profile fields, support tickets, or CMS pages. When a victim loads the page and interacts with the injected element, the retained handler runs. This enables session cookie theft, credential harvesting, cross-site request forgery against the same origin, and defacement or pivoting inside single-page applications.

javascript

// Patch excerpt: src/lib/core.js
_setCodeDataToEditor: function () {
-    const code_html = this._getCodeView();
+    const code_html = this._deleteDisallowedTags(this._getCodeView());

    if (options.fullPage) {
        const parseDocument = this._parser.parseFromString(code_html, 'text/html');

Source: GitHub commit a94ace2. The fix routes the code view through _deleteDisallowedTags before parsing, forcing namespaced and custom elements through the disallow list.

Detection Methods for CVE-2026-59167

Indicators of Compromise

Stored records containing HTML with namespaced tags (for example <x:script>, <svg:a>) or unknown custom elements combined with on* event handlers.
Outbound requests from browser sessions to unexpected domains shortly after rendering user-generated content.
Unexpected DOM mutations or dynamic <script> injections observed in application telemetry.
Application error logs showing sanitizer output that still contains on*= attributes.

Detection Strategies

Inventory front-end dependencies and flag any SunEditor bundle below 2.47.11 in package manifests, lockfiles, and vendored assets.
Add server-side content inspection that rejects persisted editor payloads containing on* handlers on non-standard or namespaced elements.
Implement browser-side Content Security Policy (CSP) violation reporting to surface inline script execution originating from rendered editor content.

Monitoring Recommendations

Monitor web application logs for POST or PUT requests with editor payloads that contain colon-prefixed tags or custom element names.
Alert on CSP script-src violations and report-uri events tied to pages that render user-authored HTML.
Track authenticated session anomalies, such as concurrent sessions or sudden privilege changes, following exposure to unpatched editor pages.

How to Mitigate CVE-2026-59167

Immediate Actions Required

Upgrade SunEditor to version 2.47.11 or later across all applications and CI pipelines.
Purge or re-sanitize stored editor content that predates the upgrade to remove previously accepted payloads.
Rotate session tokens and API keys for users who may have rendered untrusted editor content.

Patch Information

The fix is published in SunEditor release 2.47.11 and detailed in GHSA-6rf4-v2fh-m6p4. Additional discussion is available in GitHub issue #1646. Update the suneditor package via your package manager and rebuild all client bundles.

Workarounds

Apply a strict Content Security Policy that blocks inline event handlers and unauthorized script sources.
Post-process editor output through a hardened sanitizer such as DOMPurify before persistence and rendering.
Restrict editor availability to authenticated, trusted roles until the upgrade is deployed.

bash

# Upgrade SunEditor to the patched release
npm install suneditor@2.47.11

# Verify the installed version
npm ls suneditor