diff --git a/Directory.Build.props b/Directory.Build.props
index 0f1605e51e..b68e4850c0 100644
--- a/Directory.Build.props
+++ b/Directory.Build.props
@@ -24,6 +24,9 @@
                                      or $(MSBuildProjectName.EndsWith('.Analyzers.VisualBasic'))
                                      or $(MSBuildProjectName.EndsWith('.Analyzers.CSharp')))"
                                   >true</IsAnalyzerProject>
+
+    <!-- Only upgrade NuGetAudit warnings to errors for official builds. -->
+    <WarningsNotAsErrors Condition="'$(OfficialBuild)' != 'true'">$(WarningsNotAsErrors);NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors>
   </PropertyGroup>
 
   <!--
diff --git a/NuGet.config b/NuGet.config
index 0e64a3d6a6..2c9d3d9efd 100644
--- a/NuGet.config
+++ b/NuGet.config
@@ -18,6 +18,10 @@
     <!-- CsWin32 dailies -->
     <add key="winsdk" value="https://pkgs.dev.azure.com/azure-public/winsdk/_packaging/CI/nuget/v3/index.json" />
   </packageSources>
+  <auditSources>
+    <clear />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
+  </auditSources>
   <disabledPackageSources>
     <clear />
   </disabledPackageSources>
diff --git a/eng/Versions.props b/eng/Versions.props
index d2c3e90c7e..e50e3a7768 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -76,7 +76,7 @@
     <MicrosoftVisualStudioThreadingVersion>17.0.15-alpha</MicrosoftVisualStudioThreadingVersion>
     <!-- This is needed for Verify.Xunit to pull correct version of System.Speech -->
     <MicrosoftWindowsCompatibilityVersion>7.0.0</MicrosoftWindowsCompatibilityVersion>
-    <MoqPackageVersion>4.10.0</MoqPackageVersion>
+    <MoqPackageVersion>4.20.70</MoqPackageVersion>
     <FluentAssertionsVersion>6.11.0</FluentAssertionsVersion>
     <SystemComponentModelTypeConverterTestDataVersion>8.0.0-beta.23107.1</SystemComponentModelTypeConverterTestDataVersion>
     <SystemDrawingCommonTestDataVersion>8.0.0-beta.23107.1</SystemDrawingCommonTestDataVersion>
@@ -103,7 +103,7 @@
     <MicrosoftCodeAnalysisPublicApiAnalyzersVersion>$(MicrosoftCodeAnalysisAnalyzersVersion)</MicrosoftCodeAnalysisPublicApiAnalyzersVersion>
     <MicrosoftCodeAnalysisNetAnalyzersVersion>8.0.0-preview.23327.3</MicrosoftCodeAnalysisNetAnalyzersVersion>
     <StyleCopAnalyzersVersion>1.2.0-beta.556</StyleCopAnalyzersVersion>
-    <NugetPackagingVersion>6.3.4</NugetPackagingVersion>
+    <NugetPackagingVersion>6.11.0</NugetPackagingVersion>
   </PropertyGroup>
   <!-- Additional unchanging dependencies -->
   <PropertyGroup>
@@ -111,5 +111,7 @@
     <MicrosoftWindowsDesktopAppRefv30PackageVersion>3.0.0</MicrosoftWindowsDesktopAppRefv30PackageVersion>
     <NewtonsoftJsonVersion>13.0.1</NewtonsoftJsonVersion>
     <VsWherePackageVersion>2.6.7</VsWherePackageVersion>
+    <!-- Pin transitive dependency to avoid vulnerable 8.0.0 version. -->
+    <SystemFormatsAsn1PackageVersion>8.0.1</SystemFormatsAsn1PackageVersion>
   </PropertyGroup>
 </Project>
diff --git a/src/System.Windows.Forms.Analyzers.CSharp/tests/UnitTests/System.Windows.Forms.Analyzers.CSharp.Tests.csproj b/src/System.Windows.Forms.Analyzers.CSharp/tests/UnitTests/System.Windows.Forms.Analyzers.CSharp.Tests.csproj
index f694dc3208..713a40fa9b 100644
--- a/src/System.Windows.Forms.Analyzers.CSharp/tests/UnitTests/System.Windows.Forms.Analyzers.CSharp.Tests.csproj
+++ b/src/System.Windows.Forms.Analyzers.CSharp/tests/UnitTests/System.Windows.Forms.Analyzers.CSharp.Tests.csproj
@@ -17,6 +17,7 @@
     <PackageReference Include="Microsoft.CodeAnalysis.CSharp.SourceGenerators.Testing.XUnit" Version="$(MicrosoftCodeAnalysisPackagesVersion)" />
     <PackageReference Include="Verify.Xunit" Version="$(VerifyXunitVersion)" />
     <PackageReference Include="NuGet.Packaging" Version="$(NugetPackagingVersion)" />
+    <PackageReference Include="System.Formats.Asn1" Version="$(SystemFormatsAsn1PackageVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/System.Windows.Forms.Analyzers.VisualBasic/tests/UnitTests/System.Windows.Forms.Analyzers.VisualBasic.Tests/System.Windows.Forms.Analyzers.VisualBasic.Tests.vbproj b/src/System.Windows.Forms.Analyzers.VisualBasic/tests/UnitTests/System.Windows.Forms.Analyzers.VisualBasic.Tests/System.Windows.Forms.Analyzers.VisualBasic.Tests.vbproj
index 083c68dac3..32e1784ab7 100644
--- a/src/System.Windows.Forms.Analyzers.VisualBasic/tests/UnitTests/System.Windows.Forms.Analyzers.VisualBasic.Tests/System.Windows.Forms.Analyzers.VisualBasic.Tests.vbproj
+++ b/src/System.Windows.Forms.Analyzers.VisualBasic/tests/UnitTests/System.Windows.Forms.Analyzers.VisualBasic.Tests/System.Windows.Forms.Analyzers.VisualBasic.Tests.vbproj
@@ -18,6 +18,7 @@
     <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.SourceGenerators.Testing.XUnit" Version="$(MicrosoftCodeAnalysisPackagesVersion)" />
     <PackageReference Include="Verify.Xunit" Version="$(VerifyXunitVersion)" />
     <PackageReference Include="NuGet.Packaging" Version="$(NugetPackagingVersion)" />
+    <PackageReference Include="System.Formats.Asn1" Version="$(SystemFormatsAsn1PackageVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/System.Windows.Forms.Analyzers/tests/UnitTests/System.Windows.Forms.Analyzers.Tests.csproj b/src/System.Windows.Forms.Analyzers/tests/UnitTests/System.Windows.Forms.Analyzers.Tests.csproj
index 949bc02cc2..3cd07e52e7 100644
--- a/src/System.Windows.Forms.Analyzers/tests/UnitTests/System.Windows.Forms.Analyzers.Tests.csproj
+++ b/src/System.Windows.Forms.Analyzers/tests/UnitTests/System.Windows.Forms.Analyzers.Tests.csproj
@@ -20,6 +20,7 @@
     <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.CodeFix.Testing.XUnit" Version="$(MicrosoftCodeAnalysisPackagesVersion)" />
     <PackageReference Include="Microsoft.CodeAnalysis.VisualBasic.CodeRefactoring.Testing.XUnit" Version="$(MicrosoftCodeAnalysisPackagesVersion)" />
     <PackageReference Include="NuGet.Packaging" Version="$(NugetPackagingVersion)" />
+    <PackageReference Include="System.Formats.Asn1" Version="$(SystemFormatsAsn1PackageVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/System.Windows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs b/src/System.Windows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs
index 3336d68aff..a9d6babbd1 100644
--- a/src/System.Windows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs
+++ b/src/System.Windows.Forms.Design/tests/UnitTests/System/ComponentModel/Design/CollectionEditorTests.cs
@@ -602,9 +602,6 @@ public class CollectionEditorTests
             .Returns(mockEditorService.Object);
 
         Mock<DesignerTransaction> mockTransaction = new(MockBehavior.Strict);
-        mockTransaction
-            .Protected()
-            .Setup("Dispose", It.IsAny<bool>());
         mockTransaction
             .Protected()
             .Setup("OnCommit")
@@ -652,9 +649,6 @@ public class CollectionEditorTests
             .Returns(mockEditorService.Object);
 
         Mock<DesignerTransaction> mockTransaction = new(MockBehavior.Strict);
-        mockTransaction
-            .Protected()
-            .Setup("Dispose", It.IsAny<bool>());
         mockTransaction
             .Protected()
             .Setup("OnCancel")
diff --git a/src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/MaskedTextBoxTextEditorTests.cs b/src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/MaskedTextBoxTextEditorTests.cs
index 1708dd1166..7d8f32860f 100644
--- a/src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/MaskedTextBoxTextEditorTests.cs
+++ b/src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/MaskedTextBoxTextEditorTests.cs
@@ -17,7 +17,7 @@ public class MaskedTextBoxTextEditorTests
         Mock<ITypeDescriptorContext> mockContext = new(MockBehavior.Strict);
         mockContext
             .Setup(c => c.Instance)
-            .Returns(null);
+            .Returns((object?)null);
 
         Mock<IWindowsFormsEditorService> mockEditorService = new(MockBehavior.Strict);
         mockEditorService
diff --git a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AccessibleObjects/DataGridViewCellAccessibleObjectTests.cs b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AccessibleObjects/DataGridViewCellAccessibleObjectTests.cs
index fe44050343..f68dc944f2 100644
--- a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AccessibleObjects/DataGridViewCellAccessibleObjectTests.cs
+++ b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AccessibleObjects/DataGridViewCellAccessibleObjectTests.cs
@@ -465,6 +465,9 @@ public class DataGridViewCellAccessibleObjectTests : DataGridViewCell
     public void DataGridViewCellAccessibleObject_Select_HasSelectionFlagsWithoutValidDataGridView_DoesNothing()
     {
         Mock<DataGridViewCell> mockCell = new(MockBehavior.Strict);
+        mockCell
+            .SetupSet(s => s.State = DataGridViewElementStates.None)
+            .Verifiable();
         mockCell
             .SetupSet(s => s.State = DataGridViewElementStates.Visible)
             .Verifiable();
@@ -495,6 +498,9 @@ public class DataGridViewCellAccessibleObjectTests : DataGridViewCell
         Assert.True(dataGridView.IsHandleCreated);
 
         Mock<DataGridViewCell> mockCell = new(MockBehavior.Strict);
+        mockCell
+            .SetupSet(s => s.State = DataGridViewElementStates.None)
+            .Verifiable();
         mockCell
             .SetupSet(s => s.State = DataGridViewElementStates.Visible)
             .Verifiable();
@@ -525,6 +531,9 @@ public class DataGridViewCellAccessibleObjectTests : DataGridViewCell
         Assert.True(dataGridView.IsHandleCreated);
 
         Mock<DataGridViewCell> mockCell = new(MockBehavior.Strict);
+        mockCell
+            .SetupSet(s => s.State = DataGridViewElementStates.None)
+            .Verifiable();
         mockCell
             .SetupSet(s => s.State = DataGridViewElementStates.Visible)
             .Verifiable();
@@ -561,6 +570,9 @@ public class DataGridViewCellAccessibleObjectTests : DataGridViewCell
         Assert.True(dataGridView.IsHandleCreated);
 
         Mock<DataGridViewCell> mockCell = new(MockBehavior.Strict);
+        mockCell
+            .SetupSet(s => s.State = DataGridViewElementStates.None)
+            .Verifiable();
         mockCell
             .SetupSet(s => s.State = DataGridViewElementStates.Visible)
             .Verifiable();
@@ -595,6 +607,9 @@ public class DataGridViewCellAccessibleObjectTests : DataGridViewCell
         mockCell
             .SetupSet(s => s.State = DataGridViewElementStates.Visible)
             .Verifiable();
+        mockCell
+            .SetupSet(s => s.State = DataGridViewElementStates.None)
+            .Verifiable();
         mockCell
             .SetupSet(s => s.Selected = It.IsAny<bool>())
             .Verifiable();
diff --git a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ApplicationContextTests.cs b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ApplicationContextTests.cs
index daee4b4419..2a39508f20 100644
--- a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ApplicationContextTests.cs
+++ b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ApplicationContextTests.cs
@@ -1,9 +1,6 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using Moq;
-using Moq.Protected;
-
 namespace System.Windows.Forms.Tests;
 
 public class ApplicationContextTests
@@ -210,20 +207,39 @@ public class ApplicationContextTests
         Assert.Null(context.MainForm);
     }
 
+    private class TestApplicationContext : ApplicationContext
+    {
+        public TestApplicationContext() : base()
+        {
+        }
+
+        public int DisposeCallCount { get; private set; }
+
+        public int ExitThreadCoreCount { get; private set; }
+
+        protected override void Dispose(bool disposing)
+        {
+            DisposeCallCount++;
+            base.Dispose(disposing);
+        }
+
+        protected override void ExitThreadCore()
+        {
+            ExitThreadCoreCount++;
+            base.ExitThreadCore();
+        }
+    }
+
     [WinFormsFact]
     public void Dispose_Invoke_CallsDisposeDisposing()
     {
-        Mock<ApplicationContext> mockContext = new(MockBehavior.Strict);
-        mockContext
-            .Protected()
-            .Setup("Dispose", true)
-            .Verifiable();
-        mockContext.Object.Dispose();
-        mockContext.Protected().Verify("Dispose", Times.Once(), true);
+        TestApplicationContext context = new();
+        context.Dispose();
+        context.DisposeCallCount.Should().Be(1);
 
         // Call again.
-        mockContext.Object.Dispose();
-        mockContext.Protected().Verify("Dispose", Times.Exactly(2), true);
+        context.Dispose();
+        context.DisposeCallCount.Should().Be(2);
     }
 
     [WinFormsFact]
@@ -296,20 +312,13 @@ public class ApplicationContextTests
     [WinFormsFact]
     public void ExitThread_Invoke_CallsExitThreadCore()
     {
-        Mock<ApplicationContext> mockContext = new(MockBehavior.Strict);
-        mockContext
-            .Protected()
-            .Setup("ExitThreadCore")
-            .Verifiable();
-        mockContext
-            .Protected()
-            .Setup("Dispose", false);
-        mockContext.Object.ExitThread();
-        mockContext.Protected().Verify("ExitThreadCore", Times.Once());
+        TestApplicationContext context = new();
+        context.ExitThread();
+        context.ExitThreadCoreCount.Should().Be(1);
 
         // Call again.
-        mockContext.Object.ExitThread();
-        mockContext.Protected().Verify("ExitThreadCore", Times.Exactly(2));
+        context.ExitThread();
+        context.ExitThreadCoreCount.Should().Be(2);
     }
 
     [WinFormsFact]
diff --git a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AxSystemMonitorTests.cs b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AxSystemMonitorTests.cs
index db3d62e00d..352476de30 100644
--- a/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AxSystemMonitorTests.cs
+++ b/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/AxSystemMonitorTests.cs
@@ -1,6 +1,5 @@
 using System.ComponentModel;
 using System.Reflection;
-using Castle.Core.Internal;
 
 namespace System.Windows.Forms.Tests;
 
@@ -38,7 +37,7 @@ public class AxSystemMonitorTests : IDisposable
         foreach(PropertyDescriptor prop in properties)
         {
             string assemblyFromTestingControl = prop.ComponentType.Assembly.GetName().Name;
-            if (!assemblyFromTestingControl.IsNullOrEmpty()
+            if (!string.IsNullOrEmpty(assemblyFromTestingControl)
                 && assemblyFromTestingControl == assemblyNameFromType)
             {
                 testingControlProps.Add(prop.Name);
@@ -49,7 +48,7 @@ public class AxSystemMonitorTests : IDisposable
         foreach(EventDescriptor singleEvent in events)
         {
             string assemblyFromTestingControl = singleEvent.ComponentType.Assembly.GetName().Name;
-            if (!assemblyFromTestingControl.IsNullOrEmpty()
+            if (!string.IsNullOrEmpty(assemblyFromTestingControl)
                 && assemblyFromTestingControl == assemblyNameFromType)
             {
                 testingControlEvents.Add(singleEvent.Name);