title: KB4344167 security update breaks TLS Code
body: <p>Hopefully someone can help with this problem.  Recently our machines were updated with <em>KB4344167</em> which includes security updates for <em>.NET 4.7.1.</em>  Unfortunately this update has broken our code for a <code>Webrequest</code>.  When we run the code below we get this error:</p>
  
  <blockquote>
    <p>The request was aborted: Could not create SSL/TLS secure channel.</p>
  </blockquote>
  
  <pre><code>// Create a request for the URL.        
  WebRequest request = WebRequest.Create(url);
  //specify to use TLS 1.2 as default connection
  ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
  request.Timeout = int.Parse(configmanager.GetSetting("Webtimeout"));
  // Set proxy
  request.Proxy = WebRequest.DefaultWebProxy;
  request.Proxy.Credentials = CredentialCache.DefaultCredentials;
  // Define a cache policy for this request only. 
  HttpRequestCachePolicy noCachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);
  request.CachePolicy = noCachePolicy;
  ServicePointManager.ServerCertificateValidationCallback = (s, cert, chain, ssl) =&gt; true;
  // Get the response.
  HttpWebResponse response = (HttpWebResponse)request.GetResponse();
  </code></pre>
  
  <p>When the security update is uninstalled from the machine the code executes fine.  Are we missing something in the code above?  Thats about the only thing I can think of.</p>
  
  <p>Any help is greatly appreciated!</p>