HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS attacks. In HtmlSanitizer before version 5.0.372, there is a possible XSS bypass if style tag is allowed. If you have explicitly allowed the "<style>" tag, an attacker could craft HTML that includes script after passing through the sanitizer. The default settings disallow the "<style>" tag so there is no risk if you have not explicitly allowed the "<style>" tag. The problem has been fixed in version 5.0.372.