Cross-site scripting vulnerability in TinyMCE

Published: May 28, 2021
Updated: Apr 14, 2023
GHSA: <a href="https://github.com/advisories/GHSA-5vm8-hhgr-jcjp" target="_blank" rel="noopener"> GHSA-5vm8-hhgr-jcjp
Severity: Medium
Exploit:

Impact

A cross-site scripting (XSS) vulnerability was discovered in the URL sanitization logic of the core parser for form elements. The vulnerability allowed arbitrary JavaScript execution when inserting a specially crafted piece of content into the editor using the clipboard or APIs, and then submitting the form. However, as TinyMCE does not allow forms to be submitted while editing, the vulnerability could only be triggered when the content was previewed or rendered outside of the editor. This impacts all users who are using TinyMCE 5.7.0 or lower.

Patches

This vulnerability has been patched in TinyMCE 5.7.1 by improved URL sanitization logic.

Workarounds

To work around this vulnerability, either:

Upgrade to TinyMCE 5.7.1 or higher
Manually sanitize form URL attributes using a TinyMCE node filter.
Disable form elements in your content using the invalid_elements setting.

Example: Sanitizing using a node filter

editor.parser.addNodeFilter(&#039;form&#039;, function(nodes) {
  nodes.forEach(function(node) {
    if (node.attributes) {
      node.attributes.forEach(function(attr) {
        var name = attr.name;
        var value = attr.value;
        // Sanitize the attribute value here or remove it entirely
        var sanitizedValue = ...;
        node.attr(name, santizedValue);
      });
    }
  });
});