SunEditor is a lightweight and powerful WYSIWYG editor in vanilla JavaScript with no dependencies. Prior to 3.1.4, the SunEditor Embed plugin in src/plugins/modal/embed.js parses attacker-controlled raw embed HTML with DOMParser and processes the resulting DOM nodes. When an external script element follows a valid iframe, the plugin recreates a script element from the attacker-controlled src attribute and appends it to the live DOM, causing JavaScript execution in the editor page. If an application stores or reflects SunEditor content without additional backend sanitization, an attacker who can submit embed HTML can trigger stored or reflected cross-site scripting when another user opens, previews, renders, or edits the content, enabling access to page data and account actions as the victim. This issue is fixed in version 3.1.4.

Affected: npm: suneditor

Summary

A DOM-based Cross-Site Scripting (XSS) vulnerability exists in the SunEditor Embed plugin. Crafted iframe embed HTML followed by an external <script src=...> element bypasses the plugin’s sanitization logic. The plugin recreates and appends the attacker-controlled script element to the live DOM, causing JavaScript execution in the context of the editor page.

If an application stores or reflects SunEditor content without additional backend sanitization, this can lead to stored or reflected XSS when another user opens, previews, renders, or edits the malicious content.

Details

The Embed plugin parses raw embed HTML and processes the resulting DOM nodes. When a <script> element is included after a valid iframe, the plugin creates a new script element using the attacker-controlled src value and appends it to the DOM.

Relevant behavior:

const embedDOM = new DOMParser().parseFromString(src, 'text/html').body.children; if (/^script$/i.test(chd.nodeName)) { scriptTag = dom.utils.createElement('script', { src: chd.getAttribute('src'), async: 'true' }, null); continue; } cover.appendChild(scriptTag);

Because the script is newly created and appended, it executes.

PoC

Start a local server hosting a JavaScript payload:

``` mkdir -p /tmp/suneditor-poc cd /tmp/suneditor-poc

cat > poc.js <<'EOF' alert(1); console.log("SunEditor Embed Plugin XSS executed"); EOF

python3 -m http.server 8000 ```

Open SunEditor with the Embed plugin enabled, then insert the fol…