title: IE10 User-Agent causes ASP.Net to not send back Set-Cookie (IE10 not setting cookies)
body: <p><strong>Summary</strong></p>
  
  <p>ASP.Net does not send back a <code>Set-Cookie</code> header when using IE 10. Meaning that for example you cannot login to an ASP.Net site using IE10 when using Forms Authentication for example.</p>
  
  <p><strong>Detail</strong></p>
  
  <p>We're currently testing one of our legacy web apps against IE 10 [Preview 2]. </p>
  
  <p>When attempting to login using Forms Authentication, we don't get a <code>Set-Cookie</code> header in the response if the user-agent is that of IE 10. We've tried this with a blank .Net 2 and .Net 4 site.</p>
  
  <p>Because we couldn't/wouldn't believe it, we even ran the follow HTTP request manually through <code>telnet</code> - after using all usual tools - and got the same response.</p>
  
  <pre><code>GET http://test.ourdomain.co.uk/ HTTP/1.1
  Accept: */*
  Host: test.ourdomain.co.uk
  User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)
  Content-Length: 0
  </code></pre>
  
  <p>The above HTTP request returns no <code>Set-Cookie</code> in the response. Yet if we simply change the User-Agent to <code>Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/6.0)</code> it works!</p>
  
  <p>Can anyone else replicate this? I can't find any known issue with IE10 cookies other than an issue that effects non-standard URL patterns.</p>
  
  <p><strong>Hotfix</strong> </p>
  
  <p>After <a href="https://stackoverflow.com/users/21336/devio">devio</a> posted the original answer, with a workaround, <a href="https://stackoverflow.com/users/18636/nullptr">nullptr</a> has confirm that there is now a <a href="http://support.microsoft.com/kb/2600088" rel="nofollow noreferrer">hotfix for this</a>.</p>
  
  <p><a href="http://support.microsoft.com/kb/2600088" rel="nofollow noreferrer">http://support.microsoft.com/kb/2600088</a></p>
  
  <p>I've promoted the hotfix to the main question as it's just handier for future reference, but please do up-vote the users mentioned.</p>