XAML Verification
Since R2 2023 SP1 the XamlFormatProvider automatically verifies the types used in the imported XAML. It makes sure that all used types are from for the trusted assemblies. This mechanism prevents any unknown types loading and is enabled by default.
If the XAML cannot be verified the UnverifiedXamlException is thrown.
The verification can be disabled or extended with custom assemblies and types that are added via the ImportSettings settings of the XamlFormatProvider.
Disabling the Default Verification
If you are sure that the imported XAML content can be trusted, you can disable the default verification by handling the PreProcessingXaml event of the ImportSettings class.
Disable the default XAML validation
XamlFormatProvider provider = new XamlFormatProvider();
provider.ImportSettings.PreProcessingXaml += (s, args) => {
args.SkipXamlValidation = true;
};
Adding Custom Assemblies to the Allowed Assemblies
To add custom assemblies to the collection with allowed assemblies, use the AllowedAssemblies property of the XamlFormatProvider.ImportSettings.
Add assemblies to the AllowedAssemblies collection
XamlFormatProvider provider = new XamlFormatProvider();
provider.ImportSettings.AllowedAssemblies.Add("MyAssemblyName");
provider.ImportSettings.AllowedAssemblies.Add("PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35");
provider.ImportSettings.AllowedAssemblies.Add("PresentationCore, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35");
AssembliesTokens dictionary of the XamlFormatProvider.ImportSettings.
Add an assembly public key to the AssembliesTokens collection
XamlFormatProvider provider = new XamlFormatProvider();
provider.ImportSettings.AllowedAssemblies.Add("PresentationFramework");
provider.ImportSettings.AssembliesTokens["PresentationFramework"] = "31bf3856ad364e35";
Adding Custom Types to the Allowed Types
To add custom types to the collection with allowed types, use the AllowedTypes property of the XamlFormatProvider.ImportSettings.
Add types to the AllowedTypes collection
XamlFormatProvider provider = new XamlFormatProvider();
provider.ImportSettings.AllowedTypes.Add(typeof(System.Windows.Controls.Label));
provider.ImportSettings.AllowedTypes.Add(typeof(ScaleTransform));
provider.ImportSettings.AllowedTypes.Add(typeof(NullExtension));