GHSA-438c-3975-5x3f

### Impact A [cross-site scripting (XSS)](https://owasp.org/www-community/attacks/xss/) vulnerability was discovered in TinyMCE’s content insertion code. This allowed `iframe` elements containing malicious code to execute when inserted into the editor. These `iframe` elements are restricted in their permissions by same-origin browser protections, but could still trigger operations such as downloading of malicious assets.

### Fix TinyMCE 6.8.1 introduced a new `sandbox_iframes` boolean option which adds the `sandbox=""` attribute to every `iframe` element by default when enabled. This will prevent cross-origin, and in special cases same-origin, XSS by embedded resources in `iframe` elements. From TinyMCE 7.0.0 onwards the default value of this option is `true`.

In TinyMCE 7.0.0 a new `sandbox_iframes_exclusions` option was also added, allowing a list of domains to be specified that should be excluded from having the `sandbox=""` attribute applied when the `sandbox_iframes` option is enabled. By default, this option is set to an array of domains that are provided in embed code by popular websites. To sandbox `iframe` elements from every domain, set this option to `[]`.

### Workarounds The HTTP Content-Security-Policy (CSP) `frame-src` or `object-src` can be configured to restrict or block the loading of unauthorized URLS. Refer to the [TinyMCE Content Security Policy Guide](https://www.tiny.cloud/docs/tinymce/latest/tinymce-and-csp/).

### References - [TinyMCE 6.8.1](https://www.tiny.cloud/docs/tinymce/6/6.8.1-release-notes/#new-convert_unsafe_embeds-option-that-controls-whether-object-and-embed-elements-will-be-converted-to-more-restrictive-alternatives-namely-img-for-image-mime-types-video-for-video-mime-types-audio-audio-mime-types-or-iframe-for-other-or-unspecified-mime-types) - [TinyMCE 7.0.0](https://www.tiny.cloud/docs/tinymce/7/7.0-release-notes/#sandbox_iframes-editor-option-is-now-defaulted-to-true)