April 2021 CU for SharePoint 2013 product family is available for download

The product group released the April 2021 Cumulative Update for the SharePoint 2013 product family.

For April 2021 CU we have full server packages (also known as Uber packages) for all products. No other CU is required to fully patch SharePoint.

As this is a common question: Yes, April 2021 CU includes all fixes from April 2021 PU.


Be aware that all Updates for SharePoint 2013 require SharePoint Server 2013 SP1 to be installed first.

Please also have a look at the article that discusses how to properly patch a SharePoint 2013 farm which has Search enabled (see below).

Previous releases of the SharePoint Server 2013 cumulative update included both the executable and the .CAB file in the same self-extracting executable download. Because of the file size, the SharePoint Server 2013 package has been divided into several separate downloads. One contains the executable file, while the others contain the CAB file. All are necessary and must be placed in the same folder to successfully install the update. All are available by clicking the same Hotfix Download Available link in the KB article for the release.

This CU includes all SharePoint 2013 fixes (including all SharePoint 2013 security fixes) released since SP1. The CU does not include SP1. You need to install SP1 before installing this CU.

The KB articles for April 2021 CU should be available at the following locations in a couple of hours:

  • KB 4504730 – SharePoint Foundation 2013 April 2021 CU
  • KB 4504732 – SharePoint Server 2013 April 2021 CU
  • KB 4504731 – Project Server 2013 April 2021 CU
  • KB 4504729 – Office Web Apps Server 2013 April 2021 CU

The Full Server Packages for April 2021 CU are available through the following links:

After installing the fixes you need to run the SharePoint 2013 Products Configuration Wizard on each machine in the farm. If you prefer to run the command line version psconfig.exe ensure to have a look here for the correct Options.

Be aware that the SharePoint Server 2013 CU contains the SharePoint Foundation 2013 CU. And the Project Server 2013 CU also contains the SharePoint Server 2013 CU and SharePoint Foundation 2013 CU.

Please ensure to have a look at the SharePoint Patching Best Practices before applying new fixes.

Related Info:


  1. Hi Stefan,

    We have deployed the April 2021 sharepoint 2013 CU on our SharePoint farm which has 2 WFEs and 2 Apps server. The CU has been successfully deployed on all servers but getting an error one of infopath form solutions.
    Errors from ULS log:

    Exception DeserializeVersion1 failed with unhandled exception Microsoft.Office.Server.Security.SafeSerialization+BlockedTypeException: SafeSerialization[Context=EnhancedBinaryReader Deserialization]: type System.Text.StringBuilder not allowed. at Microsoft.Office.Server.Security.SafeSerialization.ValidatingSerializationBinder.ResolveAndValidateType(TypeName typeName) at Microsoft.Office.Server.Security.SafeSerialization.ValidatingSerializationBinder.BindToType(String assemblyName, String typeName) at System.Runtime.Serialization.Formatters.Binary.ObjectReader.Bind(String assemblyString, String typeString) at System.Runtime.Serialization.Formatters.Binary.ObjectReader.GetType(BinaryAssemblyInfo assemblyInfo, String name) at System.Runtime.Serialization.Formatters.Binary.ObjectMap…. 9f92c49f-b373-9089-5c4f-12f021810da6
    Exception ….ctor(String objectName, String[] memberNames, BinaryTypeEnum[] binaryTypeEnumA, Object[] typeInformationA, Int32[] memberAssemIds, ObjectReader objectReader, Int32 objectId, BinaryAssemblyInfo assemblyInfo, SizedArray assemIdToAssemblyTable) at System.Runtime.Serialization.Formatters.Binary.__BinaryParser.ReadObjectWithMapTyped(BinaryObjectWithMapTyped record) at System.Runtime.Serialization.Formatters.Binary.__BinaryParser.Run() at System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize(HeaderHandler handler, __BinaryParser serParser, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage) at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream, HeaderHandler handler, Boolean fCheck, … 9f92c49f-b373-9089-5c4f-12f021810da6
    Exception …Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage) at Microsoft.Office.InfoPath.Server.Serialization.EnhancedBinaryReader.ReadSerializable() at Microsoft.Office.InfoPath.Server.DocumentLifetime.DocumentSessionState.<>c__DisplayClassc.b__8() at Microsoft.Office.Server.Diagnostics.FirstChanceHandler.ExceptionFilter(Boolean fRethrowException, TryBlock tryBlock, FilterBlock filter, CatchBlock catchBlock, FinallyBlock finallyBlock) StackTrace: at Microsoft.Office.Server.Native.dll: (sig=9afccfd8-248d-4fb9-a01a-c8bacd6f7473|2|microsoft.office.server.native.pdb, offset=135DA) at Microsoft.Office.Server.Native.dll: (offset=21F8D) 9f92c49f-b373-9089-5c4f-12f021810da6
    Monitorable Watson bucket parameters: SharePoint Server 2013, ULSException14, 41b7c39f “infopath forms services”, 0f0011d9 “15.0.4569.0”, fd34ba92 “microsoft.office.infopath.server”, 0f0014d9 “15.0.5337.0”, 60517875 “wed mar 17 03:33:09 2021”, 0000358f “0000358f”, 00000051 “00000051”, 8f88a060 “blockedtypeexception”, 6d306d67 “m0mg” 9f92c49f-b373-9089-5c4f-12f021810da6
    Verbose Deerialization of session state failed for form template ‘ABG36QN23L6AKTUMQ52RHUTP4W3ACCJSFYYS4MZWFYYTE’ with exception of type ‘Microsoft.Office.Server.Security.SafeSerialization+BlockedTypeException, Microsoft.Office.InfoPath.Server, Version=, Culture=neutral, PublicKeyToken=71e9bce111e9429c’ and message: ‘SafeSerialization[Context=EnhancedBinaryReader Deserialization]: type System.Text.StringBuilder not allowed.’ 9f92c49f-b373-9089-5c4f-12f021810da6
    Warning Exception occurred during request processing.

    The error is very specific to related deserialization saying DeserializeVersion1 failed with unhandled exception Microsoft.Office.Server.Security.SafeSerialization+BlockedTypeException:

    Can you please help and suggest why this is causing issue.


    1. Hi Nitin,
      this has been reported as a problem in March 2021 CU (which is also included in April CU) for all product versions.
      The product group is currently investigating this.
      I would recommend to open a support case with Microsoft to ensure that your issue is properly tracked.


      1. Hi Stefan, would you happened to know a public URL/webpage where we can check on the status of this issue (infopath solution error) being resolved?



        1. Hi Leon,

          this cannot be tracked without a support ticket.



          1. Hi Stefan,
            Would you happen to know if this issue has been resolved it?

          2. Hi Randall,
            the infopath issue was resolved with June CU.

          3. Just as an FYI – I installed SharePoint updates this weekend (SharePoint 2013), had the same issue, installed the June CU and this did not resolve the issue for us.

  2. SharePoint site is access denied for all even for farm account after putting this patch


  3. Does anyone have an issue with the Security Token Services?


  4. We applied the Aug 2021 in SP 2019 and are seeing this, so apparently it was not resolved in June 2021 CU or was re-introduced. Is anyone aware of a workaround?


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