diff --git a/src/libraries/Directory.Build.targets b/src/libraries/Directory.Build.targets
index 83a2e140326c1..4bee9c66ea207 100644
--- a/src/libraries/Directory.Build.targets
+++ b/src/libraries/Directory.Build.targets
@@ -253,6 +253,19 @@
     </When>
   </Choose>
 
+  <!-- Adds ObsoleteAttribute to projects that need to apply downlevel Obsoletions with DiagnosticId and UrlFormat -->
+  <Choose>
+    <When Condition="'$(IncludeInternalObsoleteAttribute)' == 'true' and ($(TargetFramework.StartsWith('netstandard')) or $(TargetFramework.StartsWith('netcoreapp')) or '$(TargetFrameworkIdentifier)' == '.NETFramework')">
+      <ItemGroup>
+        <Compile Include="$(CoreLibSharedDir)System\ObsoleteAttribute.cs" Link="System\ObsoleteAttribute.cs" />
+      </ItemGroup>
+      <PropertyGroup>
+        <!-- Suppress CS0436 to allow ObsoleteAttribute to be internally defined and used in netstandard -->
+        <NoWarn>$(NoWarn);CS0436</NoWarn>
+      </PropertyGroup>
+    </When>
+  </Choose>
+
   <!-- The Default behavior in VS is to show files for the first target framework in TargetFrameworks property.
         This is required to show all the files corresponding to all target frameworks in VS. -->
   <ItemGroup>
diff --git a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.cs b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.cs
index e19e3c253e9dd..b14173fb6c6ef 100644
--- a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.cs
+++ b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.cs
@@ -259,6 +259,7 @@ public DirectoryServicesCOMException(string message, System.Exception inner) { }
         public string ExtendedErrorMessage { get { throw null; } }
         public override void GetObjectData(System.Runtime.Serialization.SerializationInfo serializationInfo, System.Runtime.Serialization.StreamingContext streamingContext) { }
     }
+    [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
     public sealed partial class DirectoryServicesPermission : System.Security.Permissions.ResourcePermissionBase
     {
         public DirectoryServicesPermission() { }
@@ -274,6 +275,7 @@ public enum DirectoryServicesPermissionAccess
         Browse = 2,
         Write = 6,
     }
+    [System.ObsoleteAttribute("Code Access Security is not supported or honored by the runtime.", DiagnosticId = "SYSLIB0003", UrlFormat = "https://aka.ms/dotnet-warnings/{0}")]
     [System.AttributeUsageAttribute(System.AttributeTargets.Assembly | System.AttributeTargets.Class | System.AttributeTargets.Constructor | System.AttributeTargets.Event | System.AttributeTargets.Method | System.AttributeTargets.Struct, AllowMultiple=true, Inherited=false)]
     public partial class DirectoryServicesPermissionAttribute : System.Security.Permissions.CodeAccessSecurityAttribute
     {
diff --git a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
index 68593ef6e13eb..a29cfa079c933 100644
--- a/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
+++ b/src/libraries/System.DirectoryServices/ref/System.DirectoryServices.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0</TargetFrameworks>
+    <IncludeInternalObsoleteAttribute>true</IncludeInternalObsoleteAttribute>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System.DirectoryServices.cs" />
diff --git a/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj b/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
index fe5b6232d96ab..7751f4e3d475a 100644
--- a/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
+++ b/src/libraries/System.DirectoryServices/src/System.DirectoryServices.csproj
@@ -3,6 +3,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <TargetFrameworks>$(NetCoreAppCurrent)-Windows_NT;netstandard2.0;netcoreapp2.0-Windows_NT</TargetFrameworks>
     <ExcludeCurrentNetCoreAppFromPackage>true</ExcludeCurrentNetCoreAppFromPackage>
+    <IncludeInternalObsoleteAttribute>true</IncludeInternalObsoleteAttribute>
   </PropertyGroup>
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
   <PropertyGroup>
@@ -135,6 +136,7 @@
     <Compile Include="Interop\NativeMethods.cs" />
     <Compile Include="Interop\SafeNativeMethods.cs" />
     <Compile Include="Interop\UnsafeNativeMethods.cs" />
+    <Compile Include="$(CommonPath)System\Obsoletions.cs" Link="System\Obsoletions.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)System.Security.Permissions\src\System.Security.Permissions.csproj" />
diff --git a/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermission.cs b/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermission.cs
index 7b1ebc03ec5eb..27cab3be2254c 100644
--- a/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermission.cs
+++ b/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermission.cs
@@ -5,9 +5,7 @@
 
 namespace System.DirectoryServices
 {
-#pragma warning disable SYSLIB0003
-    // Conditionally marking this type as obsolete in .NET 5+ will require diverging its net5.0 build from netstandard2.0
-    // https://github.com/dotnet/runtime/issues/39413
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
     public sealed class DirectoryServicesPermission : ResourcePermissionBase
     {
         public DirectoryServicesPermission() { }
@@ -16,5 +14,4 @@ public DirectoryServicesPermission(PermissionState state) { }
         public DirectoryServicesPermission(DirectoryServicesPermissionAccess permissionAccess, string path) { }
         public DirectoryServicesPermissionEntryCollection PermissionEntries { get; }
     }
-#pragma warning restore SYSLIB0003
 }
diff --git a/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermissionAttribute.cs b/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermissionAttribute.cs
index b4d094115b5bd..43c3986daeaa9 100644
--- a/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermissionAttribute.cs
+++ b/src/libraries/System.DirectoryServices/src/System/DirectoryServices/DirectoryServicesPermissionAttribute.cs
@@ -6,9 +6,7 @@
 
 namespace System.DirectoryServices
 {
-#pragma warning disable SYSLIB0003
-    // Conditionally marking this type as obsolete in .NET 5+ will require diverging its net5.0 build from netstandard2.0
-    // https://github.com/dotnet/runtime/issues/39413
+    [Obsolete(Obsoletions.CodeAccessSecurityMessage, DiagnosticId = Obsoletions.CodeAccessSecurityDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
     [AttributeUsage(AttributeTargets.Assembly | AttributeTargets.Class | AttributeTargets.Struct |
         AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Event,
         AllowMultiple = true, Inherited = false)]
@@ -19,5 +17,4 @@ public DirectoryServicesPermissionAttribute(SecurityAction action) : base(defaul
         public string Path { get; set; }
         public override IPermission CreatePermission() { return default(IPermission); }
     }
-#pragma warning restore SYSLIB0003
 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/ObsoleteAttribute.cs b/src/libraries/System.Private.CoreLib/src/System/ObsoleteAttribute.cs
index 11a2777e85068..05dfed0844b12 100644
--- a/src/libraries/System.Private.CoreLib/src/System/ObsoleteAttribute.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/ObsoleteAttribute.cs
@@ -24,7 +24,13 @@ namespace System
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum |
         AttributeTargets.Interface | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Event | AttributeTargets.Delegate,
         Inherited = false)]
-    public sealed class ObsoleteAttribute : Attribute
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+#nullable enable
+    internal
+#endif
+    sealed class ObsoleteAttribute : Attribute
     {
         public ObsoleteAttribute()
         {