diff --git a/src/mscorlib/src/Internal/Runtime/Augments/RuntimeThread.cs b/src/mscorlib/src/Internal/Runtime/Augments/RuntimeThread.cs
index 1ff2ff11e461..3aafe01a2ce1 100644
--- a/src/mscorlib/src/Internal/Runtime/Augments/RuntimeThread.cs
+++ b/src/mscorlib/src/Internal/Runtime/Augments/RuntimeThread.cs
@@ -47,7 +47,6 @@ private Thread AsThread()
         public bool IsBackground
         {
             get { return IsBackgroundNative(); }
-            [HostProtection(SelfAffectingThreading = true)]
             set { SetBackgroundNative(value); }
         }
 
@@ -77,7 +76,6 @@ public bool IsBackground
         public ThreadPriority Priority
         {
             get { return (ThreadPriority)GetPriorityNative(); }
-            [HostProtection(SelfAffectingThreading = true)]
             set { SetPriorityNative((int)value); }
         }
 
@@ -113,7 +111,6 @@ public ApartmentState GetApartmentState()
         ** An unstarted thread can be marked to indicate that it will host a
         ** single-threaded or multi-threaded apartment.
         =========================================================================*/
-        [HostProtection(Synchronization = true, SelfAffectingThreading = true)]
         public bool TrySetApartmentState(ApartmentState state)
         {
 #if FEATURE_COMINTEROP_APARTMENT_SUPPORT
@@ -184,10 +181,8 @@ public void DisableComObjectEagerCleanup()
         **             ThreadInterruptedException if the thread is interrupted while waiting.
         **             ThreadStateException if the thread has not been started yet.
         =========================================================================*/
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         public void Join() => JoinInternal(Timeout.Infinite);
 
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         public bool Join(int millisecondsTimeout) => JoinInternal(millisecondsTimeout);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
diff --git a/src/mscorlib/src/Microsoft/Win32/SafeHandles/SafeLibraryHandle.cs b/src/mscorlib/src/Microsoft/Win32/SafeHandles/SafeLibraryHandle.cs
index 058247e42ac4..23631987a5a9 100644
--- a/src/mscorlib/src/Microsoft/Win32/SafeHandles/SafeLibraryHandle.cs
+++ b/src/mscorlib/src/Microsoft/Win32/SafeHandles/SafeLibraryHandle.cs
@@ -6,7 +6,6 @@ namespace Microsoft.Win32 {
     using Microsoft.Win32.SafeHandles;
     using System.Security.Permissions;
 
-    [HostProtectionAttribute(MayLeakOnAbort = true)]
     sealed internal class SafeLibraryHandle : SafeHandleZeroOrMinusOneIsInvalid {
         internal SafeLibraryHandle() : base(true) {}
 
diff --git a/src/mscorlib/src/System/Collections/ArrayList.cs b/src/mscorlib/src/System/Collections/ArrayList.cs
index e784c08766de..e7f121370b6b 100644
--- a/src/mscorlib/src/System/Collections/ArrayList.cs
+++ b/src/mscorlib/src/System/Collections/ArrayList.cs
@@ -725,7 +725,6 @@ public virtual void Sort(IComparer comparer)
     
         // Returns a thread-safe wrapper around an IList.
         //
-        [HostProtection(Synchronization=true)]
         public static IList Synchronized(IList list) {
             if (list==null)
                 throw new ArgumentNullException(nameof(list));
@@ -736,7 +735,6 @@ public virtual void Sort(IComparer comparer)
     
         // Returns a thread-safe wrapper around a ArrayList.
         //
-        [HostProtection(Synchronization=true)]
         public static ArrayList Synchronized(ArrayList list) {
             if (list==null)
                 throw new ArgumentNullException(nameof(list));
diff --git a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentDictionary.cs b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentDictionary.cs
index 6f465896a8ae..c1a6f7564c6a 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentDictionary.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentDictionary.cs
@@ -40,7 +40,6 @@ namespace System.Collections.Concurrent
     [ComVisible(false)]
     [DebuggerTypeProxy(typeof(Mscorlib_DictionaryDebugView<,>))]
     [DebuggerDisplay("Count = {Count}")]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class ConcurrentDictionary<TKey, TValue> : IDictionary<TKey, TValue>, IDictionary, IReadOnlyDictionary<TKey, TValue>
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentQueue.cs b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentQueue.cs
index 4069a6b7b108..7aa597169056 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentQueue.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentQueue.cs
@@ -38,7 +38,6 @@ namespace System.Collections.Concurrent
     [ComVisible(false)]
     [DebuggerDisplay("Count = {Count}")]
     [DebuggerTypeProxy(typeof(SystemCollectionsConcurrent_ProducerConsumerCollectionDebugView<>))]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [Serializable]
     public class ConcurrentQueue<T> : IProducerConsumerCollection<T>, IReadOnlyCollection<T>
     {
diff --git a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentStack.cs b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentStack.cs
index c97e0f682380..c36d96c26c39 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/ConcurrentStack.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/ConcurrentStack.cs
@@ -45,7 +45,6 @@ namespace System.Collections.Concurrent
     /// </remarks>
     [DebuggerDisplay("Count = {Count}")]
     [DebuggerTypeProxy(typeof(SystemCollectionsConcurrent_ProducerConsumerCollectionDebugView<>))]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class ConcurrentStack<T> : IProducerConsumerCollection<T>, IReadOnlyCollection<T>
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Collections/Concurrent/OrderablePartitioner.cs b/src/mscorlib/src/System/Collections/Concurrent/OrderablePartitioner.cs
index 02263b7f97dc..33e3c88e9a6d 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/OrderablePartitioner.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/OrderablePartitioner.cs
@@ -61,7 +61,6 @@ namespace System.Collections.Concurrent
     /// </ol>
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public abstract class OrderablePartitioner<TSource> : Partitioner<TSource>
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Collections/Concurrent/Partitioner.cs b/src/mscorlib/src/System/Collections/Concurrent/Partitioner.cs
index 3d54c1471b41..0192b1942c27 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/Partitioner.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/Partitioner.cs
@@ -44,7 +44,6 @@ namespace System.Collections.Concurrent
     /// </ol>
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public abstract class Partitioner<TSource>
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Collections/Concurrent/PartitionerStatic.cs b/src/mscorlib/src/System/Collections/Concurrent/PartitionerStatic.cs
index a946abf5a6b8..9b36c053adb5 100644
--- a/src/mscorlib/src/System/Collections/Concurrent/PartitionerStatic.cs
+++ b/src/mscorlib/src/System/Collections/Concurrent/PartitionerStatic.cs
@@ -69,7 +69,6 @@ public enum EnumerablePartitionerOptions
     /// thread.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public static class Partitioner
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Collections/Hashtable.cs b/src/mscorlib/src/System/Collections/Hashtable.cs
index 0b3a6b015f38..d4c7d8d673e3 100644
--- a/src/mscorlib/src/System/Collections/Hashtable.cs
+++ b/src/mscorlib/src/System/Collections/Hashtable.cs
@@ -1046,7 +1046,6 @@ private void putEntry (bucket[] newBuckets, Object key, Object nvalue, int hashc
     
         // Returns a thread-safe wrapper for a Hashtable.
         //
-        [HostProtection(Synchronization=true)]
         public static Hashtable Synchronized(Hashtable table) {
             if (table==null)
                 throw new ArgumentNullException(nameof(table));
diff --git a/src/mscorlib/src/System/Collections/SortedList.cs b/src/mscorlib/src/System/Collections/SortedList.cs
index 0f6ab62d6b11..4a480a2c3745 100644
--- a/src/mscorlib/src/System/Collections/SortedList.cs
+++ b/src/mscorlib/src/System/Collections/SortedList.cs
@@ -528,7 +528,6 @@ public virtual Object Clone()
         
         // Returns a thread-safe SortedList.
         //
-        [HostProtection(Synchronization=true)]
         public static SortedList Synchronized(SortedList list) {
             if (list==null)
                 throw new ArgumentNullException(nameof(list));
diff --git a/src/mscorlib/src/System/Collections/Stack.cs b/src/mscorlib/src/System/Collections/Stack.cs
index d36c8e93cbcc..c3ad15abd88c 100644
--- a/src/mscorlib/src/System/Collections/Stack.cs
+++ b/src/mscorlib/src/System/Collections/Stack.cs
@@ -189,7 +189,6 @@ public Stack(ICollection col) : this((col==null ? 32 : col.Count))
     
         // Returns a synchronized Stack.
         //
-        [HostProtection(Synchronization=true)]
         public static Stack Synchronized(Stack stack) {
             if (stack==null)
                 throw new ArgumentNullException(nameof(stack));
diff --git a/src/mscorlib/src/System/Diagnostics/log.cs b/src/mscorlib/src/System/Diagnostics/log.cs
index 6c438c92e9e2..6916ce3a0a86 100644
--- a/src/mscorlib/src/System/Diagnostics/log.cs
+++ b/src/mscorlib/src/System/Diagnostics/log.cs
@@ -22,7 +22,6 @@ namespace System.Diagnostics {
    // programatically, by registry (specifics....) or environment
    // variables.
     [Serializable]
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     internal delegate void LogMessageEventHandler(LoggingLevels level, LogSwitch category, 
                                                     String message, 
                                                     StackTrace location);
diff --git a/src/mscorlib/src/System/IO/MemoryStream.cs b/src/mscorlib/src/System/IO/MemoryStream.cs
index 5dde00d18e04..bdddc8381802 100644
--- a/src/mscorlib/src/System/IO/MemoryStream.cs
+++ b/src/mscorlib/src/System/IO/MemoryStream.cs
@@ -181,7 +181,6 @@ protected override void Dispose(bool disposing)
         public override void Flush() {
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public override Task FlushAsync(CancellationToken cancellationToken) {
 
@@ -358,7 +357,6 @@ internal void InternalGetOriginAndLength(out int origin, out int length)
             return n;
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
@@ -591,7 +589,6 @@ public override void CopyTo(Stream destination, int bufferSize)
 
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
diff --git a/src/mscorlib/src/System/IO/Stream.cs b/src/mscorlib/src/System/IO/Stream.cs
index f1a3198fd99f..3cdfad613ef5 100644
--- a/src/mscorlib/src/System/IO/Stream.cs
+++ b/src/mscorlib/src/System/IO/Stream.cs
@@ -109,7 +109,6 @@ internal SemaphoreSlim EnsureAsyncActiveSemaphoreInitialized()
             }
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task CopyToAsync(Stream destination)
         {
@@ -147,14 +146,12 @@ public Task CopyToAsync(Stream destination)
             return CopyToAsync(destination, bufferSize);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task CopyToAsync(Stream destination, Int32 bufferSize)
         {
             return CopyToAsync(destination, bufferSize, CancellationToken.None);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
         {
@@ -281,14 +278,12 @@ protected virtual void Dispose(bool disposing)
 
         public abstract void Flush();
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public Task FlushAsync()
         {
             return FlushAsync(CancellationToken.None);
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public virtual Task FlushAsync(CancellationToken cancellationToken)
         {
@@ -303,14 +298,12 @@ protected virtual WaitHandle CreateWaitHandle()
             return new ManualResetEvent(false);
         }
 
-        [HostProtection(ExternalThreading=true)]
         public virtual IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
         {
             Contract.Ensures(Contract.Result<IAsyncResult>() != null);
             return BeginReadInternal(buffer, offset, count, callback, state, serializeAsynchronously: false, apm: true);
         }
 
-        [HostProtection(ExternalThreading = true)]
         internal IAsyncResult BeginReadInternal(
             byte[] buffer, int offset, int count, AsyncCallback callback, Object state, 
             bool serializeAsynchronously, bool apm)
@@ -405,14 +398,12 @@ public virtual int EndRead(IAsyncResult asyncResult)
             }
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task<int> ReadAsync(Byte[] buffer, int offset, int count)
         {
             return ReadAsync(buffer, offset, count, CancellationToken.None);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task<int> ReadAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
@@ -451,14 +442,12 @@ private struct ReadWriteParameters // struct for arguments to Read and Write cal
 
 
 
-        [HostProtection(ExternalThreading=true)]
         public virtual IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
         {
             Contract.Ensures(Contract.Result<IAsyncResult>() != null);
             return BeginWriteInternal(buffer, offset, count, callback, state, serializeAsynchronously: false, apm: true);
         }
 
-        [HostProtection(ExternalThreading = true)]
         internal IAsyncResult BeginWriteInternal(
             byte[] buffer, int offset, int count, AsyncCallback callback, Object state, 
             bool serializeAsynchronously, bool apm)
@@ -701,7 +690,6 @@ void ITaskCompletionAction.Invoke(Task completingTask)
             bool ITaskCompletionAction.InvokeMayRunArbitraryCode { get { return true; } }
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task WriteAsync(Byte[] buffer, int offset, int count)
         {
@@ -710,7 +698,6 @@ public Task WriteAsync(Byte[] buffer, int offset, int count)
 
 
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteAsync(Byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {
@@ -782,7 +769,6 @@ public virtual void WriteByte(byte value)
             Write(oneByteArray, 0, 1);
         }
 
-        [HostProtection(Synchronization=true)]
         public static Stream Synchronized(Stream stream) 
         {
             if (stream==null)
@@ -928,7 +914,6 @@ public override Task FlushAsync(CancellationToken cancellationToken)
                     Task.CompletedTask;
             }
 
-            [HostProtection(ExternalThreading = true)]
             public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
             {
                 if (!CanRead) __Error.ReadNotSupported();
@@ -945,7 +930,6 @@ public override int EndRead(IAsyncResult asyncResult)
                 return BlockingEndRead(asyncResult);
             }
 
-            [HostProtection(ExternalThreading = true)]
             public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
             {
                 if (!CanWrite) __Error.WriteNotSupported();
@@ -1217,7 +1201,6 @@ public override int ReadByte()
                     return _stream.ReadByte();
             }
         
-            [HostProtection(ExternalThreading=true)]
             public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
             {
                 bool overridesBeginRead = _stream.HasOverriddenBeginEndRead();
@@ -1271,7 +1254,6 @@ public override void WriteByte(byte b)
                     _stream.WriteByte(b);
             }
         
-            [HostProtection(ExternalThreading=true)]
             public override IAsyncResult BeginWrite(byte[] buffer, int offset, int count, AsyncCallback callback, Object state)
             {
                 bool overridesBeginWrite = _stream.HasOverriddenBeginEndWrite();
diff --git a/src/mscorlib/src/System/IO/StreamReader.cs b/src/mscorlib/src/System/IO/StreamReader.cs
index c8a502660fc1..33cca92abe61 100644
--- a/src/mscorlib/src/System/IO/StreamReader.cs
+++ b/src/mscorlib/src/System/IO/StreamReader.cs
@@ -774,7 +774,6 @@ public override String ReadLine()
         }
         
         #region Task based Async APIs
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public override Task<String> ReadLineAsync()
         {
@@ -855,7 +854,6 @@ private async Task<String> ReadLineAsyncInternal()
             return GetStringAndReleaseSharedStringBuilder(sb);
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public override Task<String> ReadToEndAsync()
         {
@@ -892,7 +890,6 @@ private async Task<String> ReadToEndAsyncInternal()
             return GetStringAndReleaseSharedStringBuilder(sb);
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public override Task<int> ReadAsync(char[] buffer, int index, int count)
         {
@@ -1080,7 +1077,6 @@ internal override async Task<int> ReadAsyncInternal(char[] buffer, int index, in
             return charsRead;
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public override Task<int> ReadBlockAsync(char[] buffer, int index, int count)
         {
diff --git a/src/mscorlib/src/System/IO/StreamWriter.cs b/src/mscorlib/src/System/IO/StreamWriter.cs
index 470e8912a465..49415d641e8d 100644
--- a/src/mscorlib/src/System/IO/StreamWriter.cs
+++ b/src/mscorlib/src/System/IO/StreamWriter.cs
@@ -395,7 +395,6 @@ public override void Write(String value)
         }
 
         #region Task based Async APIs
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteAsync(char value)
         {
@@ -457,7 +456,6 @@ public override Task WriteAsync(char value)
             _this.CharPos_Prop = charPos;
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteAsync(String value)
         {
@@ -543,7 +541,6 @@ public override Task WriteAsync(String value)
             _this.CharPos_Prop = charPos;
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteAsync(char[] buffer, int index, int count)
         {
@@ -631,7 +628,6 @@ public override Task WriteAsync(char[] buffer, int index, int count)
             _this.CharPos_Prop = charPos;
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteLineAsync()
         {
@@ -654,7 +650,6 @@ public override Task WriteLineAsync()
         }
         
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteLineAsync(char value)
         {
@@ -677,7 +672,6 @@ public override Task WriteLineAsync(char value)
         }
         
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteLineAsync(String value)
         {
@@ -700,7 +694,6 @@ public override Task WriteLineAsync(String value)
         }
 
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task WriteLineAsync(char[] buffer, int index, int count)
         {
@@ -733,7 +726,6 @@ public override Task WriteLineAsync(char[] buffer, int index, int count)
         }
         
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task FlushAsync()
         {
diff --git a/src/mscorlib/src/System/IO/TextReader.cs b/src/mscorlib/src/System/IO/TextReader.cs
index d5e5a52e0715..ca05fa4f2b42 100644
--- a/src/mscorlib/src/System/IO/TextReader.cs
+++ b/src/mscorlib/src/System/IO/TextReader.cs
@@ -172,7 +172,6 @@ public virtual String ReadLine()
         }
 
         #region Task based Async APIs
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public virtual Task<String> ReadLineAsync()
         {
@@ -183,7 +182,6 @@ public virtual Task<String> ReadLineAsync()
             this, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public async virtual Task<String> ReadToEndAsync()
         {
@@ -197,7 +195,6 @@ public async virtual Task<String> ReadToEndAsync()
             return sb.ToString();
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public virtual Task<int> ReadAsync(char[] buffer, int index, int count)
         {
@@ -228,7 +225,6 @@ internal virtual Task<int> ReadAsyncInternal(char[] buffer, int index, int count
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading=true)]
         [ComVisible(false)]
         public virtual Task<int> ReadBlockAsync(char[] buffer, int index, int count)
         {
@@ -244,7 +240,6 @@ public virtual Task<int> ReadBlockAsync(char[] buffer, int index, int count)
             return ReadBlockAsyncInternal(buffer, index, count);
          }
 
-        [HostProtection(ExternalThreading=true)]
         private async Task<int> ReadBlockAsyncInternal(char[] buffer, int index, int count)
         {
             Contract.Requires(buffer != null);
@@ -263,7 +258,6 @@ private async Task<int> ReadBlockAsyncInternal(char[] buffer, int index, int cou
         }
         #endregion
 
-        [HostProtection(Synchronization=true)]
         public static TextReader Synchronized(TextReader reader) 
         {
             if (reader==null)
diff --git a/src/mscorlib/src/System/IO/TextWriter.cs b/src/mscorlib/src/System/IO/TextWriter.cs
index de1bb0c29f02..5b460a568390 100644
--- a/src/mscorlib/src/System/IO/TextWriter.cs
+++ b/src/mscorlib/src/System/IO/TextWriter.cs
@@ -124,7 +124,6 @@ public void Dispose()
         }
     
 
-        [HostProtection(Synchronization=true)]
         public static TextWriter Synchronized(TextWriter writer) {
             if (writer==null)
                 throw new ArgumentNullException(nameof(writer));
@@ -486,7 +485,6 @@ public virtual void WriteLine (String format, params Object[] arg)
         }
 
         #region Task based Async APIs
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteAsync(char value)
         {
@@ -499,7 +497,6 @@ public virtual Task WriteAsync(char value)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteAsync(String value)
         {
@@ -512,7 +509,6 @@ public virtual Task WriteAsync(String value)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task WriteAsync(char[] buffer)
         {
@@ -520,7 +516,6 @@ public Task WriteAsync(char[] buffer)
             return WriteAsync(buffer, 0, buffer.Length);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteAsync(char[] buffer, int index, int count)
         {
@@ -533,7 +528,6 @@ public virtual Task WriteAsync(char[] buffer, int index, int count)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteLineAsync(char value)
         {
@@ -546,7 +540,6 @@ public virtual Task WriteLineAsync(char value)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteLineAsync(String value)
         {
@@ -559,7 +552,6 @@ public virtual Task WriteLineAsync(String value)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public Task WriteLineAsync(char[] buffer)
         {
@@ -567,7 +559,6 @@ public Task WriteLineAsync(char[] buffer)
             return WriteLineAsync(buffer, 0, buffer.Length);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteLineAsync(char[] buffer, int index, int count)
         {
@@ -580,14 +571,12 @@ public virtual Task WriteLineAsync(char[] buffer, int index, int count)
             tuple, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task WriteLineAsync()
         {
             return WriteAsync(CoreNewLine);
         }
 
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public virtual Task FlushAsync()
         {
diff --git a/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs b/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
index f73b5d041fb2..d78632639bb6 100644
--- a/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
+++ b/src/mscorlib/src/System/IO/UnmanagedMemoryStream.cs
@@ -265,7 +265,6 @@ protected override void Dispose(bool disposing)
             if (!_isOpen) __Error.StreamIsClosed();
         }
         
-        [HostProtection(ExternalThreading=true)] 
         [ComVisible(false)] 
         public override Task FlushAsync(CancellationToken cancellationToken) { 
         
@@ -422,7 +421,6 @@ protected override void Dispose(bool disposing)
             return nInt;
         }
         
-        [HostProtection(ExternalThreading = true)]
         [ComVisible(false)]
         public override Task<Int32> ReadAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken) {        
             if (buffer==null)
@@ -620,7 +618,6 @@ protected override void Dispose(bool disposing)
             return;
         }
         
-        [HostProtection(ExternalThreading = true)] 
         [ComVisible(false)] 
         public override Task WriteAsync(Byte[] buffer, Int32 offset, Int32 count, CancellationToken cancellationToken) { 
         
diff --git a/src/mscorlib/src/System/Reflection/Emit/AssemblyBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/AssemblyBuilder.cs
index a7d17185839a..9331ae193c2d 100644
--- a/src/mscorlib/src/System/Reflection/Emit/AssemblyBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/AssemblyBuilder.cs
@@ -156,7 +156,6 @@ public override String ImageRuntimeVersion
 
     // AssemblyBuilder class.
     // deliberately not [serializable]
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_AssemblyBuilder))]
     [ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/ConstructorBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/ConstructorBuilder.cs
index a4df0e94e7d1..ef76adcf8010 100644
--- a/src/mscorlib/src/System/Reflection/Emit/ConstructorBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/ConstructorBuilder.cs
@@ -16,7 +16,6 @@ namespace System.Reflection.Emit
     using System.Runtime.InteropServices;
     using System.Diagnostics.Contracts;
     
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_ConstructorBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/CustomAttributeBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/CustomAttributeBuilder.cs
index 1577f1188fe4..545657a053a3 100644
--- a/src/mscorlib/src/System/Reflection/Emit/CustomAttributeBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/CustomAttributeBuilder.cs
@@ -25,7 +25,6 @@ namespace System.Reflection.Emit {
     using System.Diagnostics;
     using System.Diagnostics.Contracts;
     
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_CustomAttributeBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/EnumBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/EnumBuilder.cs
index 05508865fbd2..82dc2828ca4c 100644
--- a/src/mscorlib/src/System/Reflection/Emit/EnumBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/EnumBuilder.cs
@@ -23,7 +23,6 @@ namespace System.Reflection.Emit {
     using System.Security.Permissions;
 
     
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_EnumBuilder))]
 [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/EventBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/EventBuilder.cs
index 031528089835..449b20824cd5 100644
--- a/src/mscorlib/src/System/Reflection/Emit/EventBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/EventBuilder.cs
@@ -24,7 +24,6 @@ namespace System.Reflection.Emit {
     // A EventBuilder is always associated with a TypeBuilder.  The TypeBuilder.DefineEvent
     // method will return a new EventBuilder to a client.
     // 
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_EventBuilder))]
 [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/FieldBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/FieldBuilder.cs
index 1702c7c47172..595d60ada0dd 100644
--- a/src/mscorlib/src/System/Reflection/Emit/FieldBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/FieldBuilder.cs
@@ -13,7 +13,6 @@ namespace System.Reflection.Emit
     using System.Security.Permissions;
     using System.Diagnostics.Contracts;
     
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_FieldBuilder))]
 [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/MethodBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/MethodBuilder.cs
index 8defdfa62cd6..654e166a05d7 100644
--- a/src/mscorlib/src/System/Reflection/Emit/MethodBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/MethodBuilder.cs
@@ -19,7 +19,6 @@ namespace System.Reflection.Emit
     using System.Diagnostics;
     using System.Diagnostics.Contracts;
 
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_MethodBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/ModuleBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/ModuleBuilder.cs
index 46ea6cde2fe8..6884f50b0e66 100644
--- a/src/mscorlib/src/System/Reflection/Emit/ModuleBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/ModuleBuilder.cs
@@ -50,7 +50,6 @@ public override bool Equals(object obj)
     }
 
     // deliberately not [serializable]
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_ModuleBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/PropertyBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/PropertyBuilder.cs
index 00de84c60174..e7442b4e02f3 100644
--- a/src/mscorlib/src/System/Reflection/Emit/PropertyBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/PropertyBuilder.cs
@@ -25,7 +25,6 @@ namespace System.Reflection.Emit {
     // A PropertyBuilder is always associated with a TypeBuilder.  The TypeBuilder.DefineProperty
     // method will return a new PropertyBuilder to a client.
     // 
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_PropertyBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/TypeBuilder.cs b/src/mscorlib/src/System/Reflection/Emit/TypeBuilder.cs
index f6c101869a4f..73778d5f2736 100644
--- a/src/mscorlib/src/System/Reflection/Emit/TypeBuilder.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/TypeBuilder.cs
@@ -35,7 +35,6 @@ public enum PackingSize
         Size128                     = 128,
     }
 
-    [HostProtection(MayLeakOnAbort = true)]
     [ClassInterface(ClassInterfaceType.None)]
     [ComDefaultInterface(typeof(_TypeBuilder))]
     [System.Runtime.InteropServices.ComVisible(true)]
diff --git a/src/mscorlib/src/System/Reflection/Emit/UnmanagedMarshal.cs b/src/mscorlib/src/System/Reflection/Emit/UnmanagedMarshal.cs
index 09eac3a27234..28e95e24560a 100644
--- a/src/mscorlib/src/System/Reflection/Emit/UnmanagedMarshal.cs
+++ b/src/mscorlib/src/System/Reflection/Emit/UnmanagedMarshal.cs
@@ -10,7 +10,6 @@ namespace System.Reflection.Emit
 
     // This class is describing the fieldmarshal.
     [Serializable]
-    [HostProtection(MayLeakOnAbort = true)]
     [System.Runtime.InteropServices.ComVisible(true)]
     [Obsolete("An alternate API is available: Emit the MarshalAs custom attribute instead. http://go.microsoft.com/fwlink/?linkid=14202")]
     public sealed class UnmanagedMarshal
diff --git a/src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs b/src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs
index 2723fcf79167..6a16462383f3 100644
--- a/src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs
+++ b/src/mscorlib/src/System/Runtime/CompilerServices/AsyncMethodBuilder.cs
@@ -32,7 +32,6 @@ namespace System.Runtime.CompilerServices
     /// Provides a builder for asynchronous methods that return void.
     /// This type is intended for compiler use only.
     /// </summary>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct AsyncVoidMethodBuilder
     {
         /// <summary>The synchronization context associated with this operation.</summary>
@@ -271,7 +270,6 @@ private Task Task
     /// Prior to being copied, one of its Task, SetResult, or SetException members must be accessed,
     /// or else the copies may end up building distinct Task instances.
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct AsyncTaskMethodBuilder
     {
         /// <summary>A cached VoidTaskResult task used for builders that complete synchronously.</summary>
@@ -418,7 +416,6 @@ internal void SetNotificationForWaitCompletion(bool enabled)
     /// Prior to being copied, one of its Task, SetResult, or SetException members must be accessed,
     /// or else the copies may end up building distinct Task instances.
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct AsyncTaskMethodBuilder<TResult>
     {
         /// <summary>A cached task for default(TResult).</summary>
diff --git a/src/mscorlib/src/System/Runtime/CompilerServices/TaskAwaiter.cs b/src/mscorlib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
index 61aa077c6b07..98a81ea470b7 100644
--- a/src/mscorlib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
+++ b/src/mscorlib/src/System/Runtime/CompilerServices/TaskAwaiter.cs
@@ -57,7 +57,6 @@ namespace System.Runtime.CompilerServices
 {
     /// <summary>Provides an awaiter for awaiting a <see cref="System.Threading.Tasks.Task"/>.</summary>
     /// <remarks>This type is intended for compiler use only.</remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct TaskAwaiter : ICriticalNotifyCompletion
     {
         /// <summary>The task being awaited.</summary>
@@ -291,7 +290,6 @@ private static Action OutputWaitEtwEvents(Task task, Action continuation)
 
     /// <summary>Provides an awaiter for awaiting a <see cref="System.Threading.Tasks.Task{TResult}"/>.</summary>
     /// <remarks>This type is intended for compiler use only.</remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct TaskAwaiter<TResult> : ICriticalNotifyCompletion
     {
         /// <summary>The task being awaited.</summary>
@@ -372,7 +370,6 @@ public ConfiguredTaskAwaitable.ConfiguredTaskAwaiter GetAwaiter()
 
         /// <summary>Provides an awaiter for a <see cref="ConfiguredTaskAwaitable"/>.</summary>
         /// <remarks>This type is intended for compiler use only.</remarks>
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         public struct ConfiguredTaskAwaiter : ICriticalNotifyCompletion
         {
             /// <summary>The task being awaited.</summary>
@@ -459,7 +456,6 @@ public ConfiguredTaskAwaitable<TResult>.ConfiguredTaskAwaiter GetAwaiter()
 
         /// <summary>Provides an awaiter for a <see cref="ConfiguredTaskAwaitable{TResult}"/>.</summary>
         /// <remarks>This type is intended for compiler use only.</remarks>
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         public struct ConfiguredTaskAwaiter : ICriticalNotifyCompletion
         {
             /// <summary>The task being awaited.</summary>
diff --git a/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs b/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
index 5881b6414fe8..86789bf12d5a 100644
--- a/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
+++ b/src/mscorlib/src/System/Runtime/CompilerServices/YieldAwaitable.cs
@@ -48,7 +48,6 @@ public struct YieldAwaitable
 
         /// <summary>Provides an awaiter that switches into a target environment.</summary>
         /// <remarks>This type is intended for compiler use only.</remarks>
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         public struct YieldAwaiter : ICriticalNotifyCompletion
         {
             /// <summary>Gets whether a yield is not required.</summary>
diff --git a/src/mscorlib/src/System/Runtime/GcSettings.cs b/src/mscorlib/src/System/Runtime/GcSettings.cs
index fc70183508cc..91997f5297b8 100644
--- a/src/mscorlib/src/System/Runtime/GcSettings.cs
+++ b/src/mscorlib/src/System/Runtime/GcSettings.cs
@@ -47,7 +47,6 @@ public static GCLatencyMode LatencyMode
             }
 
             // We don't want to allow this API when hosted.
-            [HostProtection(MayLeakOnAbort = true)]
             [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
             set 
             {
@@ -71,7 +70,6 @@ public static GCLargeObjectHeapCompactionMode LargeObjectHeapCompactionMode
             }
 
             // We don't want to allow this API when hosted.
-            [HostProtection(MayLeakOnAbort = true)]
             [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
             set 
             {
diff --git a/src/mscorlib/src/System/Threading/AutoResetEvent.cs b/src/mscorlib/src/System/Threading/AutoResetEvent.cs
index 6fe6c062323a..78a6fa12343d 100644
--- a/src/mscorlib/src/System/Threading/AutoResetEvent.cs
+++ b/src/mscorlib/src/System/Threading/AutoResetEvent.cs
@@ -17,7 +17,6 @@ namespace System.Threading {
     using System.Security.Permissions;
     using System.Runtime.InteropServices;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [System.Runtime.InteropServices.ComVisible(true)]
     public sealed class AutoResetEvent : EventWaitHandle
     {
diff --git a/src/mscorlib/src/System/Threading/CancellationToken.cs b/src/mscorlib/src/System/Threading/CancellationToken.cs
index fc767988ed90..5b78f20900f1 100644
--- a/src/mscorlib/src/System/Threading/CancellationToken.cs
+++ b/src/mscorlib/src/System/Threading/CancellationToken.cs
@@ -39,7 +39,6 @@ namespace System.Threading
     /// </para>
     /// </remarks>
     [ComVisible(false)]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerDisplay("IsCancellationRequested = {IsCancellationRequested}")]
     public struct CancellationToken
     {
diff --git a/src/mscorlib/src/System/Threading/CancellationTokenRegistration.cs b/src/mscorlib/src/System/Threading/CancellationTokenRegistration.cs
index 34e0bb0aba12..ac27fe30e66d 100644
--- a/src/mscorlib/src/System/Threading/CancellationTokenRegistration.cs
+++ b/src/mscorlib/src/System/Threading/CancellationTokenRegistration.cs
@@ -17,7 +17,6 @@ namespace System.Threading
     /// <remarks>
     /// To unregister a callback, dispose the corresponding Registration instance.
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct CancellationTokenRegistration : IEquatable<CancellationTokenRegistration>, IDisposable
     {
         private readonly CancellationCallbackInfo m_callbackInfo;
diff --git a/src/mscorlib/src/System/Threading/CancellationTokenSource.cs b/src/mscorlib/src/System/Threading/CancellationTokenSource.cs
index d1f0039a1a1a..fe9e0dec7671 100644
--- a/src/mscorlib/src/System/Threading/CancellationTokenSource.cs
+++ b/src/mscorlib/src/System/Threading/CancellationTokenSource.cs
@@ -36,7 +36,6 @@ namespace System.Threading
     /// </para>
     /// </remarks>
     [ComVisible(false)]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
 
     public class CancellationTokenSource : IDisposable
     {
diff --git a/src/mscorlib/src/System/Threading/CountdownEvent.cs b/src/mscorlib/src/System/Threading/CountdownEvent.cs
index f984fb351ca9..d86a2ccfb880 100644
--- a/src/mscorlib/src/System/Threading/CountdownEvent.cs
+++ b/src/mscorlib/src/System/Threading/CountdownEvent.cs
@@ -32,7 +32,6 @@ namespace System.Threading
     /// </remarks>
     [ComVisible(false)]
     [DebuggerDisplay("Initial Count={InitialCount}, Current Count={CurrentCount}")]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class CountdownEvent : IDisposable
     {
         // CountdownEvent is a simple synchronization primitive used for fork/join parallelism. We create a
diff --git a/src/mscorlib/src/System/Threading/EventWaitHandle.cs b/src/mscorlib/src/System/Threading/EventWaitHandle.cs
index faaafff47ab6..4b1611c6aaf6 100644
--- a/src/mscorlib/src/System/Threading/EventWaitHandle.cs
+++ b/src/mscorlib/src/System/Threading/EventWaitHandle.cs
@@ -37,7 +37,6 @@ namespace System.Threading
     using System.Security.AccessControl;
     using System.Diagnostics.Contracts;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [ComVisibleAttribute(true)]
     public class EventWaitHandle : WaitHandle
     {
diff --git a/src/mscorlib/src/System/Threading/LazyInitializer.cs b/src/mscorlib/src/System/Threading/LazyInitializer.cs
index 36f2cec82e5e..238cc89dbdfa 100644
--- a/src/mscorlib/src/System/Threading/LazyInitializer.cs
+++ b/src/mscorlib/src/System/Threading/LazyInitializer.cs
@@ -55,7 +55,6 @@ public enum LazyThreadSafetyMode
     /// These routines avoid needing to allocate a dedicated, lazy-initialization instance, instead using
     /// references to ensure targets have been initialized as they are accessed.
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public static class LazyInitializer
     {
         /// <summary>
diff --git a/src/mscorlib/src/System/Threading/ManualResetEvent.cs b/src/mscorlib/src/System/Threading/ManualResetEvent.cs
index 504cfb423cf9..00041567dfa3 100644
--- a/src/mscorlib/src/System/Threading/ManualResetEvent.cs
+++ b/src/mscorlib/src/System/Threading/ManualResetEvent.cs
@@ -17,7 +17,6 @@ namespace System.Threading {
     using System.Security.Permissions;
     using System.Runtime.InteropServices;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
 [System.Runtime.InteropServices.ComVisible(true)]
     public sealed class ManualResetEvent : EventWaitHandle
     {        
diff --git a/src/mscorlib/src/System/Threading/ManualResetEventSlim.cs b/src/mscorlib/src/System/Threading/ManualResetEventSlim.cs
index dc83fac391f8..509af5bfa04e 100644
--- a/src/mscorlib/src/System/Threading/ManualResetEventSlim.cs
+++ b/src/mscorlib/src/System/Threading/ManualResetEventSlim.cs
@@ -47,7 +47,6 @@ namespace System.Threading
     /// </remarks>
     [ComVisible(false)]
     [DebuggerDisplay("Set = {IsSet}")]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class ManualResetEventSlim : IDisposable
     {
         // These are the default spin counts we use on single-proc and MP machines.
diff --git a/src/mscorlib/src/System/Threading/Monitor.cs b/src/mscorlib/src/System/Threading/Monitor.cs
index bb0c59210f9b..94dec13d0562 100644
--- a/src/mscorlib/src/System/Threading/Monitor.cs
+++ b/src/mscorlib/src/System/Threading/Monitor.cs
@@ -27,7 +27,6 @@ namespace System.Threading {
     using System.Diagnostics;
     using System.Diagnostics.Contracts;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [System.Runtime.InteropServices.ComVisible(true)]
     public static class Monitor 
     {
diff --git a/src/mscorlib/src/System/Threading/Mutex.cs b/src/mscorlib/src/System/Threading/Mutex.cs
index dba5df016bf6..506abb7a07a8 100644
--- a/src/mscorlib/src/System/Threading/Mutex.cs
+++ b/src/mscorlib/src/System/Threading/Mutex.cs
@@ -27,7 +27,6 @@ namespace System.Threading
     using System.Diagnostics;
     using System.Diagnostics.Contracts;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [ComVisible(true)]
     public sealed class Mutex : WaitHandle
     {
diff --git a/src/mscorlib/src/System/Threading/ReaderWriterLock.cs b/src/mscorlib/src/System/Threading/ReaderWriterLock.cs
index 65127fb202f2..e35ac7685b36 100644
--- a/src/mscorlib/src/System/Threading/ReaderWriterLock.cs
+++ b/src/mscorlib/src/System/Threading/ReaderWriterLock.cs
@@ -25,7 +25,6 @@ namespace System.Threading {
     using System.Runtime.Versioning;
     using System.Diagnostics.Contracts;
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [ComVisible(true)]
     public sealed class ReaderWriterLock: CriticalFinalizerObject
     {
diff --git a/src/mscorlib/src/System/Threading/SemaphoreSlim.cs b/src/mscorlib/src/System/Threading/SemaphoreSlim.cs
index a04e43d49972..92d760d77d89 100644
--- a/src/mscorlib/src/System/Threading/SemaphoreSlim.cs
+++ b/src/mscorlib/src/System/Threading/SemaphoreSlim.cs
@@ -40,7 +40,6 @@ namespace System.Threading
     /// </para>
     /// </remarks>
     [ComVisible(false)]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerDisplay("Current Count = {m_currentCount}")]
     public class SemaphoreSlim : IDisposable
     {
diff --git a/src/mscorlib/src/System/Threading/SpinLock.cs b/src/mscorlib/src/System/Threading/SpinLock.cs
index 998ea38fd37d..1d90890d6ebf 100644
--- a/src/mscorlib/src/System/Threading/SpinLock.cs
+++ b/src/mscorlib/src/System/Threading/SpinLock.cs
@@ -55,7 +55,6 @@ namespace System.Threading
     /// </para>
     /// </remarks>
     [ComVisible(false)]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerTypeProxy(typeof(SystemThreading_SpinLockDebugView))]
     [DebuggerDisplay("IsHeld = {IsHeld}")]
     public struct SpinLock
diff --git a/src/mscorlib/src/System/Threading/SpinWait.cs b/src/mscorlib/src/System/Threading/SpinWait.cs
index da913ea9e68b..1b31407e0f45 100644
--- a/src/mscorlib/src/System/Threading/SpinWait.cs
+++ b/src/mscorlib/src/System/Threading/SpinWait.cs
@@ -70,7 +70,6 @@ namespace System.Threading
     /// threads must spin, each should use its own instance of SpinWait.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public struct SpinWait
     {
 
diff --git a/src/mscorlib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs b/src/mscorlib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
index 48e0f4e7cf1a..c7a96b0394aa 100644
--- a/src/mscorlib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/ConcurrentExclusiveSchedulerPair.cs
@@ -28,7 +28,6 @@ namespace System.Threading.Tasks
     /// Provides concurrent and exclusive task schedulers that coordinate to execute
     /// tasks while ensuring that concurrent tasks may run concurrently and exclusive tasks never do.
     /// </summary>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerDisplay("Concurrent={ConcurrentTaskCountForDebugger}, Exclusive={ExclusiveTaskCountForDebugger}, Mode={ModeForDebugger}")]
     [DebuggerTypeProxy(typeof(ConcurrentExclusiveSchedulerPair.DebugView))]
     public class ConcurrentExclusiveSchedulerPair
diff --git a/src/mscorlib/src/System/Threading/Tasks/FutureFactory.cs b/src/mscorlib/src/System/Threading/Tasks/FutureFactory.cs
index 974d42783038..c98e219e8686 100644
--- a/src/mscorlib/src/System/Threading/Tasks/FutureFactory.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/FutureFactory.cs
@@ -39,7 +39,6 @@ namespace System.Threading.Tasks
     /// <see cref="System.Threading.Tasks.Task{TResult}.Factory">Task{TResult}.Factory</see> property.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class TaskFactory<TResult>
     {
         // Member variables, DefaultScheduler, other properties and ctors 
diff --git a/src/mscorlib/src/System/Threading/Tasks/Parallel.cs b/src/mscorlib/src/System/Threading/Tasks/Parallel.cs
index ae785593f85c..7808943870ee 100644
--- a/src/mscorlib/src/System/Threading/Tasks/Parallel.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/Parallel.cs
@@ -142,7 +142,6 @@ internal int EffectiveMaxConcurrencyLevel
     /// The <see cref="T:System.Threading.Tasks.Parallel"/> class provides library-based data parallel replacements
     /// for common operations such as for loops, for each loops, and execution of a set of statements.
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public static class Parallel
     {
         // static counter for generating unique Fork/Join Context IDs to be used in ETW events
diff --git a/src/mscorlib/src/System/Threading/Tasks/ParallelLoopState.cs b/src/mscorlib/src/System/Threading/Tasks/ParallelLoopState.cs
index 4e9755569ada..6a62cf897731 100644
--- a/src/mscorlib/src/System/Threading/Tasks/ParallelLoopState.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/ParallelLoopState.cs
@@ -26,7 +26,6 @@ namespace System.Threading.Tasks
     /// Enables iterations of <see cref="T:System.Threading.Tasks.Parallel"/> loops to interact with
     /// other iterations.
     /// </summary>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerDisplay("ShouldExitCurrentIteration = {ShouldExitCurrentIteration}")]
     public class ParallelLoopState
     {
diff --git a/src/mscorlib/src/System/Threading/Tasks/Task.cs b/src/mscorlib/src/System/Threading/Tasks/Task.cs
index 865ea131c2b2..cf081f75fd4c 100644
--- a/src/mscorlib/src/System/Threading/Tasks/Task.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/Task.cs
@@ -137,7 +137,6 @@ public enum TaskStatus
     /// InternalWait method serves a potential marker for when a Task is entering a wait operation.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerTypeProxy(typeof(SystemThreadingTasks_TaskDebugView))]
     [DebuggerDisplay("Id = {Id}, Status = {Status}, Method = {DebuggerDisplayMethodDescription}")]
     public class Task : IThreadPoolWorkItem, IAsyncResult, IDisposable
diff --git a/src/mscorlib/src/System/Threading/Tasks/TaskCompletionSource.cs b/src/mscorlib/src/System/Threading/Tasks/TaskCompletionSource.cs
index 822ac9b7acfc..320f704f09c2 100644
--- a/src/mscorlib/src/System/Threading/Tasks/TaskCompletionSource.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/TaskCompletionSource.cs
@@ -48,7 +48,6 @@ namespace System.Threading.Tasks
     /// </remarks>
     /// <typeparam name="TResult">The type of the result value assocatied with this <see
     /// cref="TaskCompletionSource{TResult}"/>.</typeparam>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class TaskCompletionSource<TResult>
     {
         private readonly Task<TResult> m_task;
diff --git a/src/mscorlib/src/System/Threading/Tasks/TaskFactory.cs b/src/mscorlib/src/System/Threading/Tasks/TaskFactory.cs
index 9e3bd2ec1f5a..aa4c2df74b7c 100644
--- a/src/mscorlib/src/System/Threading/Tasks/TaskFactory.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/TaskFactory.cs
@@ -38,7 +38,6 @@ namespace System.Threading.Tasks
     /// <see cref="System.Threading.Tasks.Task.Factory">Task.Factory</see> property.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class TaskFactory
     {
         // member variables
diff --git a/src/mscorlib/src/System/Threading/Tasks/TaskScheduler.cs b/src/mscorlib/src/System/Threading/Tasks/TaskScheduler.cs
index 6ff7ceb41d84..fad3fc06c565 100644
--- a/src/mscorlib/src/System/Threading/Tasks/TaskScheduler.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/TaskScheduler.cs
@@ -41,7 +41,6 @@ namespace System.Threading.Tasks
     /// </remarks>
     [DebuggerDisplay("Id={Id}")]
     [DebuggerTypeProxy(typeof(SystemThreadingTasks_TaskSchedulerDebugView))]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public abstract class TaskScheduler
     {
         ////////////////////////////////////////////////////////////
diff --git a/src/mscorlib/src/System/Threading/Tasks/future.cs b/src/mscorlib/src/System/Threading/Tasks/future.cs
index 5a250966ab8b..0c3fec89b73f 100644
--- a/src/mscorlib/src/System/Threading/Tasks/future.cs
+++ b/src/mscorlib/src/System/Threading/Tasks/future.cs
@@ -65,7 +65,6 @@ namespace System.Threading.Tasks
     /// and may be used from multiple threads concurrently.
     /// </para>
     /// </remarks>
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     [DebuggerTypeProxy(typeof(SystemThreadingTasks_FutureDebugView<>))]
     [DebuggerDisplay("Id = {Id}, Status = {Status}, Method = {DebuggerDisplayMethodDescription}, Result = {DebuggerDisplayResultDescription}")]
     public class Task<TResult> : Task
diff --git a/src/mscorlib/src/System/Threading/Thread.cs b/src/mscorlib/src/System/Threading/Thread.cs
index 2022c0533c7c..8294c20c4deb 100644
--- a/src/mscorlib/src/System/Threading/Thread.cs
+++ b/src/mscorlib/src/System/Threading/Thread.cs
@@ -271,7 +271,6 @@ internal unsafe ThreadHandle GetNativeHandle()
         **
         ** Exceptions: ThreadStateException if the thread has already been started.
         =========================================================================*/
-        [HostProtection(Synchronization=true,ExternalThreading=true)]
         [MethodImplAttribute(MethodImplOptions.NoInlining)] // Methods containing StackCrawlMark local var has to be marked non-inlineable
         public new void Start()
         {
@@ -279,7 +278,6 @@ public new void Start()
             Start(ref stackMark);
         }
 
-        [HostProtection(Synchronization=true,ExternalThreading=true)]
         [MethodImplAttribute(MethodImplOptions.NoInlining)] // Methods containing StackCrawlMark local var has to be marked non-inlineable
         public new void Start(object parameter)
         {
@@ -395,7 +393,6 @@ public void Abort()
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         private extern void AbortInternal();
 
-        [HostProtection(Synchronization=true, ExternalThreading=true)]
         public bool Join(TimeSpan timeout)
         {
             long tm = (long)timeout.TotalMilliseconds;
@@ -438,11 +435,9 @@ public static void Sleep(TimeSpan timeout)
            a explict busy loop because the hardware can be informed that it is busy waiting. */
 
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
-        [HostProtection(Synchronization=true,ExternalThreading=true)]
         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
         private static extern void SpinWaitInternal(int iterations);
 
-        [HostProtection(Synchronization=true,ExternalThreading=true)]
         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
         public static new void SpinWait(int iterations)
         {
@@ -451,11 +446,9 @@ public static new void SpinWait(int iterations)
 
         [DllImport(JitHelpers.QCall, CharSet = CharSet.Unicode)]
         [SuppressUnmanagedCodeSecurity]
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
         private static extern bool YieldInternal();
 
-        [HostProtection(Synchronization = true, ExternalThreading = true)]
         [ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
         public static new bool Yield()
         {
@@ -529,14 +522,12 @@ public ApartmentState ApartmentState
                 return (ApartmentState)GetApartmentStateNative();
             }
 
-            [HostProtection(Synchronization=true, SelfAffectingThreading=true)]
             set
             {
                 SetApartmentStateNative((int)value, true);
             }
         }
 
-        [HostProtection(Synchronization=true, SelfAffectingThreading=true)]
         public void SetApartmentState(ApartmentState state)
         {
             bool result = SetApartmentStateHelper(state, true);
@@ -552,7 +543,6 @@ public void SetApartmentState(ApartmentState state)
         ** Allocates an un-named data slot. The slot is allocated on ALL the
         ** threads.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static LocalDataStoreSlot AllocateDataSlot()
         {
             return LocalDataStoreManager.AllocateDataSlot();
@@ -563,7 +553,6 @@ public static LocalDataStoreSlot AllocateDataSlot()
         ** threads.  Named data slots are "public" and can be manipulated by
         ** anyone.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static LocalDataStoreSlot AllocateNamedDataSlot(String name)
         {
             return LocalDataStoreManager.AllocateNamedDataSlot(name);
@@ -574,7 +563,6 @@ public static LocalDataStoreSlot AllocateNamedDataSlot(String name)
         ** allocated.  Named data slots are "public" and can be manipulated by
         ** anyone.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static LocalDataStoreSlot GetNamedDataSlot(String name)
         {
             return LocalDataStoreManager.GetNamedDataSlot(name);
@@ -585,7 +573,6 @@ public static LocalDataStoreSlot GetNamedDataSlot(String name)
         ** threads.  Named data slots are "public" and can be manipulated by
         ** anyone.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static void FreeNamedDataSlot(String name)
         {
             LocalDataStoreManager.FreeNamedDataSlot(name);
@@ -594,7 +581,6 @@ public static void FreeNamedDataSlot(String name)
         /*=========================================================================
         ** Retrieves the value from the specified slot on the current thread, for that thread's current domain.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static Object GetData(LocalDataStoreSlot slot)
         {
             LocalDataStoreHolder dls = s_LocalDataStore;
@@ -611,7 +597,6 @@ public static Object GetData(LocalDataStoreSlot slot)
         /*=========================================================================
         ** Sets the data in the specified slot on the currently running thread, for that thread's current domain.
         =========================================================================*/
-        [HostProtection(SharedState=true, ExternalThreading=true)]
         public static void SetData(LocalDataStoreSlot slot, Object data)
         {
             LocalDataStoreHolder dls = s_LocalDataStore;
@@ -682,7 +667,6 @@ public static void SetData(LocalDataStoreSlot slot, Object data)
                 }
             }
 
-            [HostProtection(ExternalThreading=true)]
             set {
                 if (value == null) {
                     throw new ArgumentNullException(nameof(value));
@@ -900,7 +884,6 @@ public static int GetDomainID()
             get {
                 return m_Name;
             }
-            [HostProtection(ExternalThreading=true)]
             set {
                 lock(this) {
                     if (m_Name != null)
diff --git a/src/mscorlib/src/System/Threading/ThreadLocal.cs b/src/mscorlib/src/System/Threading/ThreadLocal.cs
index 3495891a5066..2b996cb34dc1 100644
--- a/src/mscorlib/src/System/Threading/ThreadLocal.cs
+++ b/src/mscorlib/src/System/Threading/ThreadLocal.cs
@@ -35,7 +35,6 @@ namespace System.Threading
     /// </remarks>
     [DebuggerTypeProxy(typeof(SystemThreading_ThreadLocalDebugView<>))]
     [DebuggerDisplay("IsValueCreated={IsValueCreated}, Value={ValueForDebugDisplay}, Count={ValuesCountForDebugDisplay}")]
-    [HostProtection(Synchronization = true, ExternalThreading = true)]
     public class ThreadLocal<T> : IDisposable
     {
 
diff --git a/src/mscorlib/src/System/Threading/ThreadPool.cs b/src/mscorlib/src/System/Threading/ThreadPool.cs
index 3af006be2d19..451b15d22feb 100644
--- a/src/mscorlib/src/System/Threading/ThreadPool.cs
+++ b/src/mscorlib/src/System/Threading/ThreadPool.cs
@@ -1341,7 +1341,6 @@ static internal void PerformWaitOrTimerCallback(Object state, bool timedOut)
                                        NativeOverlapped* pOVERLAP // ptr to OVERLAP structure
                                        );   
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     public static class ThreadPool
     {
 
diff --git a/src/mscorlib/src/System/Threading/Timer.cs b/src/mscorlib/src/System/Threading/Timer.cs
index 02f7308d12c7..5bfefccad2b2 100644
--- a/src/mscorlib/src/System/Threading/Timer.cs
+++ b/src/mscorlib/src/System/Threading/Timer.cs
@@ -756,7 +756,6 @@ public bool Close(WaitHandle notifyObject)
     }
 
 
-    [HostProtection(Synchronization=true, ExternalThreading=true)]
     [System.Runtime.InteropServices.ComVisible(true)]
     public sealed class Timer : MarshalByRefObject, IDisposable
     {