CA3076: Insecure XSLT Script Execution

Article
09/06/2023

Property	Value
Rule ID	CA3076
Title	Insecure XSLT Script Execution
Category	Security
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 8	No

Cause

If you execute Extensible Stylesheets Language Transformations (XSLT) in .NET applications insecurely, the processor may resolve untrusted URI references that could disclose sensitive information to attackers, leading to Denial of Service and Cross-Site attacks. For more information, see XSLT Security Considerations(.NET Guide).

Rule description

XSLT is a World Wide Web Consortium (W3C) standard for transforming XML data. XSLT is typically used to write style sheets to transform XML data to other formats such as HTML, fixed-length text, comma-separated text, or a different XML format. Although prohibited by default, you may choose to enable it for your project.

To ensure you're not exposing an attack surface, this rule triggers whenever the XslCompiledTransform.Load receives insecure combination instances of XsltSettings and XmlResolver, which allows malicious script processing.

How to fix violations

Replace the insecure XsltSettings argument with XsltSettings.Default or with an instance that has disabled document function and script execution.
Replace the XmlResolver argument with null or an XmlSecureResolver instance.

When to suppress warnings

Unless you're sure that the input is known to be from a trusted source, do not suppress a rule from this warning.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA3076
// The code that's violating the rule is on this line.
#pragma warning restore CA3076

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA3076.severity = none

For more information, see How to suppress code analysis warnings.

Pseudo-code examples

Violation that uses XsltSettings.TrustedXslt

using System.Xml;
using System.Xml.Xsl;

namespace TestNamespace
{
    class TestClass
    {
         void TestMethod()
        {
             XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
             var settings = XsltSettings.TrustedXslt;
             var resolver = new XmlUrlResolver();
             xslCompiledTransform.Load("testStylesheet", settings, resolver); // warn
        }
    }
}

Solution that uses XsltSettings.Default

using System.Xml;
using System.Xml.Xsl;

namespace TestNamespace
{
    class TestClass
    {
        void TestMethod()
        {
            XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
            var settings = XsltSettings.Default;
            var resolver = new XmlUrlResolver();
            xslCompiledTransform.Load("testStylesheet", settings, resolver);
        }
    }
}

Violation—document function and script execution not disabled

using System.Xml;
using System.Xml.Xsl;

namespace TestNamespace
{
    class TestClass
    {
        private static void TestMethod(XsltSettings settings)
        {
            try
            {
                XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
                var resolver = new XmlUrlResolver();
                xslCompiledTransform.Load("testStylesheet", settings, resolver); // warn
            }
            catch { throw; }
            finally { }
        }
    }
}

Solution—disable document function and script execution

using System.Xml;
using System.Xml.Xsl;

namespace TestNamespace
{
    class TestClass
    {
        private static void TestMethod(XsltSettings settings)
        {
            try
            {
                XslCompiledTransform xslCompiledTransform = new XslCompiledTransform();
                settings.EnableDocumentFunction = false;
                settings.EnableScript = false;
                var resolver = new XmlUrlResolver();
                xslCompiledTransform.Load("testStylesheet", settings, resolver);
            }
            catch { throw; }
            finally { }
        }
    }
}

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