Silverstripe Framework is a PHP framework which powers the Silverstripe CMS. Prior to 5.3.23, bad actor with access to edit content in the CMS could send a specifically crafted encoded payload to the server, which could be used to inject a JavaScript payload on the front end of the site. The payload would be sanitized on the client-side, but server-side sanitization doesn't catch it. The server-side sanitization logic has been updated to sanitize against this attack. This vulnerability is fixed in 5.3.23.

Silverstripe Framework has a XSS vulnerability in HTML editor