Do you have a SharePoint Server that has been patched with KB4457916 or KB4457035? These updates can break SharePoint’s Workflow Engine. This causes errors with both SharePoint Designer Workflow and Nintex

Here are my notes based on this article:https://blogs.msdn.microsoft.com/rodneyviana/2018/09/13/after-installing-net-security-patches-to-address-cve-2018-8421-sharepoint-workflows-stop-working/

Here’s the fix:

Edit the SharePoint Web.Config file Path: C:\inetpub\wwwroot\wss\VirtualDirectories\sharepoint80\Web.Config

 In the Web.Config file, find this section:

   <System.Workflow.ComponentModel.WorkflowCompiler>

    <authorizedTypes>

      <targetFx version=”v4.0″>

I added these lines. Note the last line is specific to Nintex:

               <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeBinaryOperatorExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodePrimitiveExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeMethodInvokeExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeMethodReferenceExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeFieldReferenceExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeThisReferenceExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodePropertyReferenceExpression” Authorized=”True” />

              <authorizedType Assembly=”System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″ NameSpace=”System.CodeDom” TypeName=”CodeTypeReferenceExpression” Authorized=”True” />

 The server needed an IISRESET after the update