HttpListener Access Denied

Question

I am writing an HTTP server in C    When I try to execute the function HttpListener Start   I get an HttpListenerException saying       Access Denied     When I run the app in admin mode in windows 7 it works fine   Can I make it run without admin mode  if yes how  If not how can I make the app change to admin mode after start running   using System  using System Net   namespace ConsoleApplication1       class Program               private HttpListener httpListener   null           static void Main string   args                        Program p   new Program                p Server                       public void Server                         this httpListener   new HttpListener                 if  httpListener IsListening                  throw new InvalidOperationException  Server is currently running                  httpListener Prefixes Clear                httpListener Prefixes Add  http     4444                  try                               httpListener Start      Throws Exception                           catch  HttpListenerException ex                                if  ex Message Contains  Access is denied                                          return                                    else                                       throw

User · Answer

Thanks all  it was of great help  Just to add more  from MS page    Warning Top-level wildcard bindings  http     8080  and http     8080  should not be used  Top-level wildcard bindings can open up your app to security vulnerabilities  This applies to both strong and weak wildcards  Use explicit host names rather than wildcards  Subdomain wildcard binding  for example    mysub com  doesn t have this security risk if you control the entire parent domain  as opposed to   com  which is vulnerable   See rfc7230 section-5 4 for more information

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Unfortunately  for some reasons probably linked with HTTPS and certificates  the native  NET HttpListener requires admin privileges  and even for HTTP only protocol    The good point It is interesting to note that HTTP protocol is on top of TCP protocol  but launching a C  TCP listener doesn t require any admin privileges to run  In other words  it is conceptually possible to implement an HTTP server which do not requires admin privileges  Alternative Below  an example of project which doesn t require admin privileges  https   github com EmilianoElMariachi ElMariachi Http Server

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httpListener Prefixes Add  http     4444       you use     so you execute following cmd as admin  netsh http add urlacl url http     4444  user username   no use    must use    because you spec   4444    https   msdn microsoft com en-us library system net httplistener aspx

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The syntax was wrong for me  you must include the quotes   netsh http add urlacl url  http     4200   user everyone   otherwise I received  The parameter is incorrect

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I also faced similar problem If you have already reserved url then you have to first delete the url to run in non admin mode else it will fail with Access is Denied error   netsh http delete urlacl url http     80

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As an alternative that doesn t require elevation or netsh you could also use TcpListener for instance   The following is a modified excerpt of this sample  https   github com googlesamples oauth-apps-for-windows tree master OAuthDesktopApp     Generates state and PKCE values  string state   randomDataBase64url 32   string code verifier   randomDataBase64url 32   string code challenge   base64urlencodeNoPadding sha256 code verifier    const string code challenge method    S256       Creates a redirect URI using an available port on the loopback address  var listener   new TcpListener IPAddress Loopback  0   listener Start    string redirectURI   string Format  http    0   1     IPAddress Loopback    IPEndPoint listener LocalEndpoint  Port   output  redirect URI      redirectURI       Creates the OAuth 2 0 authorization request  string authorizationRequest   string Format   0  response type code amp scope openid 20profile amp redirect uri  1  amp client id  2  amp state  3  amp code challenge  4  amp code challenge method  5        authorizationEndpoint      System Uri EscapeDataString redirectURI       clientID      state      code challenge      code challenge method       Opens request in the browser  System Diagnostics Process Start authorizationRequest       Waits for the OAuth authorization response  var client   await listener AcceptTcpClientAsync        Read response  var response   ReadString client       Brings this app back to the foreground  this Activate        Sends an HTTP response to the browser  WriteStringAsync client    lt html gt  lt head gt  lt meta http-equiv  refresh  content  10 url https   google com  gt  lt  head gt  lt body gt Please close this window and return to the app  lt  body gt  lt  html gt    ContinueWith t   gt        client Dispose        listener Stop         Console WriteLine  HTTP server stopped             TODO  Check the response here to get the authorization code and verify the code challenge   The read and write methods being   private string ReadString TcpClient client        var readBuffer   new byte client ReceiveBufferSize       string fullServerReply   null       using  var inStream   new MemoryStream                  var stream   client GetStream             while  stream DataAvailable                        var numberOfBytesRead   stream Read readBuffer  0  readBuffer Length               if  numberOfBytesRead  lt   0                  break               inStream Write readBuffer  0  numberOfBytesRead                      fullServerReply   Encoding UTF8 GetString inStream ToArray                return fullServerReply     private Task WriteStringAsync TcpClient client  string str        return Task Run      gt                using  var writer   new StreamWriter client GetStream    new UTF8Encoding false                          writer Write  HTTP 1 0 200 OK                writer Write Environment NewLine               writer Write  Content-Type  text html  charset UTF-8                writer Write Environment NewLine               writer Write  Content-Length      str Length               writer Write Environment NewLine               writer Write Environment NewLine               writer Write str

User · Answer

You can start your application as administrator if you add Application Manifest to your project   Just Add New Item to your project and select  Application Manifest File   Change the  lt requestedExecutionLevel gt  element to    lt requestedExecutionLevel level  requireAdministrator  uiAccess  false    gt

User · Answer

In case you want to use the flag  user Everyone  you need to adjust it to your system language  In english it is as mentioned   netsh http add urlacl url http     80  user Everyone   In german it would be   netsh http add urlacl url http     80  user Jeder

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If you use http   localhost 80  as a prefix  you can listen to http requests with no need for Administrative privileges

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By default Windows defines the following prefix that is available to everyone  http     80 Temporary Listen Addresses   So you can register your HttpListener via   Prefixes Add  http     80 Temporary Listen Addresses     Guid NewGuid   ToString  D           This sometimes causes problems with software such as Skype which will try to utilise port 80 by default

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Can I make it run without admin mode  if yes how  If not how can I make the app change to admin mode after start running    You can t  it has to start with elevated privileges  You can restart it with the runas verb  which will prompt the user to switch to admin mode  static void RestartAsAdmin         var startInfo   new ProcessStartInfo  yourApp exe     Verb    runas         Process Start startInfo       Environment Exit 0         EDIT  actually  that s not true  HttpListener can run without elevated privileges  but you need to give permission for the URL on which you want to listen  See Darrel Miller s answer for details

User · Answer

Yes you can run HttpListener in non-admin mode   All you need to do is grant permissions to the particular URL   e g   netsh http add urlacl url http     80 MyUri user DOMAIN user   Documentation is here

[windows-7] HttpListener Access Denied

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