EWS web application pool stops after the February 2023 Security Update is installed

Symptoms 

After you install the Exchange Server February 2023 Security Update on Microsoft Exchange Server 2019 or 2016, the Exchange Web Services (EWS) web application pool stops responding under certain circumstances. When this occurs, clients that use the EWS protocol experience connectivity issues. 

Additionally, the following Event ID 4999 is logged in the Application log: 

E12IIS, c-RTL-AMD64, 15.01.2507.021, w3wp#MSExchangeServicesAppPool, M.Exchange.Diagnostics, M.E.D.ChainedSerializationBinder.EnforceBlockReason, M.E.Diagnostics.BlockedDeserializeTypeException, 437c-dumptidset, 15.01.2507.021.

Resolution  

This issue is fixed in the March 2023 Security Update for Exchange Server. Follow these steps:

1. Install the March 2023 security update.

2. If you applied the workaround that was provided previously in this article, follow these steps to revert the changes:

   1. Remove the following registry value:
      
      Subkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\v15\Diagnostics 
      Value:  DisableBaseTypeCheckForDeserialization
      Type: String 
      Data: 1
      
      Alternatively, run the following command to remove the registry value: 
      
      Remove-ItemProperty -Path HKLM:\SOFTWARE\Microsoft\ExchangeServer\v15\Diagnostics -Name "DisableBaseTypeCheckForDeserialization"

   2. Remove the setting override by running the following command: 

      Get-SettingOverride | Where-Object {$_.ComponentName -eq "Data" -and $_.SectionName -eq "DeserializationBinderSettings" -and $_.Parameters -eq "LearningLocations=ClientExtensionCollectionFormatter"} | Remove-SettingOverride

   3. Refresh the VariantConfiguration argument by running the following command: 
       
      Get-ExchangeDiagnosticInfo -Process Microsoft.Exchange.Directory.TopologyService -Component VariantConfiguration -Argument Refresh
       
      Note This command is optional. This setting should become effective automatically within one hour.

   4. To apply the new settings, restart the World Wide Web Publishing service and the Windows Process Activation Service (WAS). To do this, run the following command:  
       
      Restart-Service -Name W3SVC, WAS -Force  
       
      Note This command is optional. The services should restart automatically within one hour.