include::../why-dotnet.adoc[]

=== Noncompliant code example

For https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.formatters.binary.binaryformatter?view=netframework-4.8[BinaryFormatter], https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.netdatacontractserializer?view=netframework-4.8[NetDataContractSerializer], https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.formatters.soap.soapformatter?view=netframework-4.8[SoapFormatter] serializers:

[source,csharp]
----
var myBinaryFormatter = new BinaryFormatter();
myBinaryFormatter.Deserialize(stream); // Noncompliant: a binder is not used to limit types during deserialization
----

https://docs.microsoft.com/en-us/dotnet/api/system.web.script.serialization.javascriptserializer?view=netframework-4.8[JavaScriptSerializer] should not use SimpleTypeResolver or other weak resolvers:

[source,csharp]
----
JavaScriptSerializer serializer1 = new JavaScriptSerializer(new SimpleTypeResolver()); // Noncompliant: SimpleTypeResolver is unsecure (every types is resolved)
serializer1.Deserialize<ExpectedType>(json);
----

https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.losformatter?view=netframework-4.8[LosFormatter] should not be used without MAC verification:

[source,csharp]
----
LosFormatter formatter = new LosFormatter(); // Noncompliant
formatter.Deserialize(fs);
----

=== Compliant solution

https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.formatters.binary.binaryformatter?view=netframework-4.8[BinaryFormatter], https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.netdatacontractserializer?view=netframework-4.8[NetDataContractSerializer ], https://docs.microsoft.com/en-us/dotnet/api/system.runtime.serialization.formatters.soap.soapformatter?view=netframework-4.8[SoapFormatter] serializers should use a binder implementing a whitelist approach to limit types during deserialization (at least one exception should be thrown or a null value returned):

[source,csharp]
----
sealed class CustomBinder : SerializationBinder
{
   public override Type BindToType(string assemblyName, string typeName)
   {
       if (!(typeName == "type1" || typeName == "type2" || typeName == "type3"))
       {
          throw new SerializationException("Only type1, type2 and type3 are allowed"); // Compliant
       }
       return Assembly.Load(assemblyName).GetType(typeName);
   }
}

var myBinaryFormatter = new BinaryFormatter();
myBinaryFormatter.Binder = new CustomBinder();
myBinaryFormatter.Deserialize(stream);
----

https://docs.microsoft.com/en-us/dotnet/api/system.web.script.serialization.javascriptserializer?view=netframework-4.8[JavaScriptSerializer] should use a resolver implementing a whitelist to limit types during deserialization (at least one exception should be thrown or a null value  returned):

[source,csharp]
----
public class CustomSafeTypeResolver : JavaScriptTypeResolver
{
   public override Type ResolveType(string id)
   {
      if(id != "ExpectedType") {
         throw new ArgumentNullException("Only ExpectedType is allowed during deserialization"); // Compliant
      }
      return Type.GetType(id);
   }
}

JavaScriptSerializer serializer = new JavaScriptSerializer(new CustomSafeTypeResolver()); // Compliant
serializer.Deserialize<ExpectedType>(json);
----
https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.losformatter?view=netframework-4.8[LosFormatter] serializer with MAC verification:

[source,csharp]
----
LosFormatter formatter = new LosFormatter(true, secret); // Compliant
formatter.Deserialize(fs);
----

include::../resources.adoc[]

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== Implementation Specification
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== Comments And Links
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