User code might be blocked when third-party assemblies access sensitive properties (KB5004581)

Symptoms

When third-party assemblies try to access some sensitive properties, user code might be blocked. When this issue occurs, “8gaol” event entries are logged in SharePoint Unified Logging System (ULS) logs. 

Cause

To help maintain security, third-party assemblies are prevented from accessing some sensitive properties.

Resolution

To resolve this issue, install one of the following updates:

• Description of the security update for SharePoint Server 2019: August 10, 2021 (KB5002000)

• Description of the security update for SharePoint Enterprise Server 2016: August 10, 2021 (KB5002002)

• August 10, 2021, update for SharePoint Foundation 2013 (KB5002013)

To enable trusted third-party assemblies to access the sensitive properties in the Web.config file, add them to the assembly list.

For example, assume that you find the following message in ULS logs: 

In this case, follow these steps: 

1. Add a new AllowAccessSensitivePropertiesAssemblies section under SharePoint SafeMode in the Web.config file:
   
   <SharePoint>
      <SafeMode>
         <AllowAccessSensitivePropertiesAssemblies>
         </AllowAccessSensitivePropertiesAssemblies>
      …
      </SafeMode>
      …
   </SharePoint>

2. For each third-party assembly, add an entry that has an assembly full name in the AllowAccessSensitivePropertiesAssemblies section:
   
   <AllowAccessSensitivePropertiesAssemblies>
      <AllowAccessSensitivePropertiesAssembly Assembly="XXX, Version=XXX, Culture=XXX, PublicKeyToken=XXXX"/>
   </AllowAccessSensitivePropertiesAssemblies>