If we sent request body without mime types of file parameters then request throws an exception: "Error parsing MIME multipart body part header byte 271 of data segment System.Byte[]." with a next stack:

" at System.Net.Http.Formatting.Parsers.MimeMultipartBodyPartParser.<ParseBuffer>d__0.MoveNext()
at System.Net.Http.HttpContentMultipartExtensions.MoveNextPart(MultipartAsyncContext context)
at System.Net.Http.HttpContentMultipartExtensions.MultipartWriteSegmentAsyncComplete(IAsyncResult result)
at System.Runtime.Remoting.Messaging.AsyncResult.SyncProcessMessage(IMessage msg)
at System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(IMessage msg, IMessageSink replySink)
at System.Threading.ExecutionContext.runTryCode(Object userData)
at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
at System.Threading.ThreadPoolWorkQueue.Dispatch()
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()"

and as a result of unhandled exception it crushes w3wp.exe. Web api controller action:

[HttpPost]

    public Task<HttpResponseMessage> Post()
    {
        // Checks content type
        if (Request.Content.IsMimeMultipartContent())
        {
            // For returning non-async stuff, use a TaskCompletionSource to avoid thread switches
            // Save file
            var provider = new MultipartFormDataStreamProvider(_uploadPath);
            var postActionHandler = new PostActionHandler();

            return Request.Content.ReadAsMultipartAsync(provider)
                .ContinueWith(contents =>
                              HttpMultipartForm.HandleMultipartBody(contents.Result, provider),
                              TaskScheduler.FromCurrentSynchronizationContext())
                .ContinueWith(bodyParts =>
                              postActionHandler.Execute(bodyParts.Result),
                              TaskScheduler.FromCurrentSynchronizationContext());
        }

        // Only multipart form-data accepted
        var completionSource = new TaskCompletionSource<HttpResponseMessage>();
        completionSource.SetResult(Request.CreateResponse(HttpStatusCode.BadRequest));

        return completionSource.Task;
    }

How we should handle such type of exception to prevent crashes of the IIS worker process?

P.S. It's important because after the few invalid requests to that action IIS Thread pool stopped with a message "Application pool 'e4a15a24-2234-4f87-b655-d82b1e734234' is being automatically disabled due to a series of failures in the process(es) serving that application pool." and on each bad request it logs a message "A process serving application pool 'e4a15a24-2234-4f87-b655-d82b1e734234' suffered a fatal communication error with the Windows Process Activation Service. The process id was '2100'. The data field contains the error number."

readTask =>
{
    if (readTask.IsCanceled)
    {
        return Request.CreateResponse(HttpStatusCode.RequestTimeout);
    }
    else if (readTask.IsFaulted)
    {
        Exception error = readTask.Exception.GetBaseException();
        return Request.CreateErrorResponse(HttpStatusCode.BadRequest, error);
    }
    else
    {
        HttpMultipartForm.HandleMultipartBody(contents.Result, provider);
    }
},
TaskScheduler.FromCurrentSynchronizationContext())