How can I programmatically edit the hosts file in Windows 7/Server 2008?

Question

I'm writing a little WPF utility to manage entries in the hosts file for dev purposes. As you might know the hosts file is protected by the newer OSs (Win 7/2008/Vista).

I've added a manifest to my application to set the requestedExecutionLevel to "requireAdministrator", as detailed here (using "the easy way") and in the related question here.

Unfortunately this has not worked for me. There is no elevation prompt when I start the app, and calling File.AppendText for the hosts file still causes a System.UnauthorizedAccessException to be thrown: "Access to the path 'C:\Windows\System32\drivers\etc\hosts' is denied."

HostsChanger.exe.manifest:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<assemblyIdentity version="1.0.0.0" processorArchitecture="X86" name="HostsChanger" type="win32"/>
<trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
    <security>
        <requestedPrivileges>
            <requestedExecutionLevel level="requireAdministrator"/>
        </requestedPrivileges>
    </security>
</trustInfo>
</assembly>

Any ideas?

Answer 1

I'm not sure if it'll make any difference but your manifest snippet is slightly different from my understanding of how it should be (though that might be different versions):

<?xml version="1.0" encoding="utf-8"?>
<asmv1:assembly manifestVersion="1.0" xmlns="urn:schemas-microsoft-com:asm.v1" xmlns:asmv1="urn:schemas-microsoft-com:asm.v1" xmlns:asmv2="urn:schemas-microsoft-com:asm.v2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"&gt;
   <assemblyIdentity version="1.0.0.0" name="HostsChanger" />
   <trustInfo xmlns="urn:schemas-microsoft-com:asm.v2">
      <security>
         <requestedPrivileges xmlns="urn:schemas-microsoft-com:asm.v3">
            <requestedExecutionLevel level="requireAdministrator" uiAccess="false" />
         </requestedPrivileges>
      </security>
   </trustInfo>
</asmv1:assembly>

Otherwise, a work around might be to have a separate "Loader" app that the user starts with and that only starts your real WPF tool using the Verb runas as detailed in this blog post (so Process.StartInfo.Verb = "runas";).

Answer 2

I am going to take a stab in the dark here and say that it is an authenticode signature issue. I have not heard you mention anything about signing your application. As far as my understanding goes, unlike Vista, in Windows 2008/7 the only way to run an application elevated is to have a signed application manifest that identifies the privilege level that the application needs. If you need help signing, here's an article on how to sign your application: http://msdn.microsoft.com/en-us/library/bb756995.aspx

Answer 3

Paraphrased from my earlier comment, turned into an answer:

The answer ho1 gave contains an app.manifest that is exactly the same as the app I'm working on at work, and elevation is working for it. The difference here is that the filename is "app.manifest", and the project option "Manifest" (on the Application tab) is pointing to it.