Severity: moderate

    Cross-Site Scripting

    tinymce

    Overview

    There is an XSS vulnerability in tinymce before version 5.7.1.

    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('form', 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);
          });
        }
      });
    });

    Example: Using invalid_elements

    invalid_elements: 'form'

    Acknowledgements

    Tiny Technologies would like to thank Mikhail Khramenkov at Solar Security Research Team for discovering this vulnerability.

    References

    https://www.tiny.cloud/docs/release-notes/release-notes571/#securityfixes

    For more information

    If you have any questions or comments about this advisory:

    Remediation

    Upgrade to version 5.7.1 or later

    Resources

    Have content suggestions? Visit npmjs.com/support.

    Advisory timeline

    1. published

      Advisory Published
      Jun 1st, 2021
    2. reported

      Reported by Anonymous
      May 28th, 2021