HtmlSanitizer is a class for cleaning HTML fragments from constructs that can lead to XSS attacks. It uses the excellent C# jQuery port CsQuery to parse, manipulate, and render HTML and CSS.
In order to facilitate different use cases, HtmlSanitizer can be customized at several levels:
- Configure allowed HTML tags through the property
AllowedTags. All other tags will be stripped. - Configure allowed HTML attributes through the property
AllowedAttributes. All other attributes will be stripped. - Configure allowed CSS property names through the property
AllowedCssProperties. All other styles will be stripped. - Configure allowed URI schemes through the property
AllowedCssProperties. All other URIs will be stripped. - Configure HTML attributes that contain URIs (such as "src", "href" etc.) through the property
UriAttributes. - Provide a base URI that will be used to resolve relative URIs against.
Install the HtmlSanitizer NuGet package. Then:
var sanitizer = new HtmlSanitizer();
var html = @"<script>alert('xss')</script><div onload=""alert('xss')"""
+ @"style=""background-color: test"">Test<img src=""test.gif"""
+ @"style=""background-image: url(javascript:alert('xss')); margin: 10px""></div>";
var sanitized = sanitizer.Sanitize(html, "https://www.example.com");
Assert.That(sanitized, Is.EqualTo(@"<div style=""background-color: test"">"
+ @"Test<img style=""margin: 10px"" src=""https://www.example.com/test.gif""></div>");