TwilioRequestValidator 中的瞬态 System.Security.Cryptography.CryptographicException

Question

So we have our Twilio callbacks setup to validate incoming requests, via the TwilioRequestValidator documented here .

However, something we're seeing, is that the production server will run for weeks with no problems, and then suddenly start failing with a CryptographicException. This causes all incoming Twilio requests to fail.

We have a call-stack (thanks to Azure Application Insights):

    System.Security.Cryptography.CryptographicException:
   at System.Security.Cryptography.CryptographicException.ThrowCryptographicException (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Security.Cryptography.Utils.HashData (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Security.Cryptography.SHA1CryptoServiceProvider.HashCore (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Security.Cryptography.HashAlgorithm.TransformBlock (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Security.Cryptography.HMAC.HashCore (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at System.Security.Cryptography.HashAlgorithm.ComputeHash (mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089)
   at Twilio.Security.RequestValidator.GetValidationSignature (Twilio, Version=5.14.1.0, Culture=neutral, PublicKeyToken=null)
   at Misc.TwilioRequestValidator.ValidateTwilioRequestAttribute.IsValidRequest (RCHHRATool, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null)
   at Misc.TwilioRequestValidator.ValidateTwilioRequestAttribute.OnActionExecuting (RCHHRATool, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker+AsyncInvocationWithFilters.InvokeActionMethodFilterAsynchronouslyRecursive (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker+AsyncInvocationWithFilters.InvokeActionMethodFilterAsynchronouslyRecursive (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker+<>c__DisplayClass33.<BeginInvokeActionMethodWithFilters>b__31 (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncResultBase`1.Begin (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeActionMethodWithFilters (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker+<>c__DisplayClass21.<BeginInvokeAction>b__19 (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncResultBase`1.Begin (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Controller.<BeginExecuteCore>b__1c (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncVoid`1.CallBeginDelegate (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncResultBase`1.Begin (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Controller.BeginExecuteCore (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncResultBase`1.Begin (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Controller.BeginExecute (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__4 (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncVoid`1.CallBeginDelegate (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.Async.AsyncResultWrapper+WrappedAsyncResultBase`1.Begin (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.Mvc.MvcHandler.BeginProcessRequest (System.Web.Mvc, Version=5.2.3.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Web.HttpApplication+CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute (System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Web.HttpApplication+<>c__DisplayClass285_0.<ExecuteStepImpl>b__0 (System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Web.HttpApplication.ExecuteStepImpl (System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Web.HttpApplication.ExecuteStep (System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)

And we have some application code, here:

[AttributeUsage(AttributeTargets.Method)]
public class ValidateTwilioRequestAttribute : ActionFilterAttribute
{
    private readonly RequestValidator _requestValidator;

    public ValidateTwilioRequestAttribute()
    {
        var authToken = ConfigurationManager.AppSettings["TwilioAuthToken"];
        _requestValidator = new RequestValidator(authToken);
    }

    public override void OnActionExecuting(ActionExecutingContext actionContext)
    {
        var context = actionContext.HttpContext;
        if (!IsValidRequest(context.Request))
        {
            actionContext.Result = new HttpStatusCodeResult(HttpStatusCode.Forbidden);
        }

        base.OnActionExecuting(actionContext);
    }

    private bool IsValidRequest(HttpRequestBase request)
    {
        var signature = request.Headers["X-Twilio-Signature"];
        Debug.WriteLine(request.Headers["X-Twilio-Signature"]);
        //var requestUrl = request.RawUrl;
        var requestUrl = rewriteUri(request.Url.AbsoluteUri);
        Debug.WriteLine("URI is: " + rewriteUri(request.Url.AbsoluteUri));

        return _requestValidator.Validate(requestUrl, request.Form, signature);
    }

    private string rewriteUri(string absoluteUri)
    {
        //check to make sure we're not replacing 'https' with 'httpss'
        if (!absoluteUri.Contains("https"))
        {
            return Regex.Replace(absoluteUri, @"http", "https");
        }
        return absoluteUri;
    }
}

Any ideas on what could be causing this? Ideally, I'd like to handle this exception state, but I'm not sure how to handle the exception without knowing what the cause is.

EDIT: I'm getting this error message when I drill into the exception in application insights:

"Hash not valid for use in specified state."

EDIT #2: A quick search on that error messages digs up this interesting discussion on the thread safety of the Cryptography object.

Answer 1

Looks like this is a bug in the Twilio-csharp library. I believe they're using their Sha1 member in a non-thread safe manner.

I've hacked up a solution to re-init the class in the event of a CryptographicException. Since a server restart is fixing the issue, I think a force re-init of the class is called for.

    try
    {
        return _requestValidator.Validate(requestUrl, request.Form, signature);
    }
    catch (CryptographicException e)
    {
        //if the request fails, re-init the class and try again
        var authToken = ConfigurationManager.AppSettings["TwilioAuthToken"];
        _requestValidator = new RequestValidator(authToken);
        return IsValidRequest(request);
    }

EDIT: Worth noting that this fix is causing knock-on issues related to the non-thread safe manner in which the library is used.