All versions of the popular UI for ASP.NET AJAX RadEditor Control product by Telerik may be affected by a high-risk stored attribute-based cross-site scripting (XSS) vulnerability that is assigned CVE-2014-4958. This WYSIWYG rich text editor is ...what Microsoft chose to use in MSDN, CodePlex, TechNet, MCMS and even as an alternative to the default editor in SharePoint.
Personally tested and confirmed are versions: 2014.1.403.35 (much newer) and 2009.3.1208.20 (much older) using Internet Explorer 8, version 8.0.7601.17514. However, all versions from Telerik at this time may be vulnerable and will continue to be until a patched is released. A workaround may be available.
More information on the vulnerability: http://maverickblogging.com/disclosing-cve-2014-4958-stored-attribute-based-cross-site-scripting-xss-vulnerability-in-telerik-ui-for-asp-net-ajax-radeditor-control/
Remediation: Telerik states: We have applied a patch to the editor that will be delivered with our Q3 edition of the controls that should be released towards the end of October. A blog post on the issue has been published here: http://blogs.telerik.com/blogs/14-09-24/securing-radeditor-content-and-preventing-xss-attacks
Additional credit goes to Tyler Hoyle and the rest of my team in CGI Federals Emerging Technologies Security Practice for their hard work.