Thursday, February 28, 2008

Impersonating a Built-in Service Account in a Console Application

Here's a quick way to impersonate a built-in service account (NT AUTHORITY\NETWORK SERVICE or NT AUTHORITY\LOCAL SERVICE) or for that matter the Local System account (NT AUTHORITY\SYSTEM) in a console application. This might be useful for debugging or testing permissions etc. - the default application pool identity for SharePoint virtual servers is the Network Service account.

The trick is to run your code as Local System and from there you can impersonate the service accounts by using the appropriate username with no password. One way to run your code as the Local System account is to create a command line shell by using the technique shown below (taken from this orginal post), and execute your assembly from there. Calling System.Diagnostics.Debugger.Break() in your code allows you to debug.

To create a command-line shell that runs under the local system account, open a new command line window and enter:

c:\sc create testsvc binpath= "cmd /K start" type= own type= interact


followed by:

c:\sc start testsvc


A new command window should have opened up. In that window run your application.exe - you'll see that you're now running as the built-in System user account. After you've finished testing, you can delete the test service you created by entering:

c:\sc delete testsvc


Some sample impersonation code that includes an impersonation class modified slightly from the code in this post follows:


using System;
using System.Diagnostics;
using System.Security.Principal;
using System.Runtime.InteropServices;
using System.ComponentModel;
 
namespace DevHoleDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Debugger.Break();
            Console.WriteLine(WindowsIdentity.GetCurrent().Name);
            using (Impersonation imp = new Impersonation(BuiltinUser.NetworkService))
            {
                Console.WriteLine(WindowsIdentity.GetCurrent().Name);
            }
        }
 
        /// <summary>
        /// An impersonation class (modified from http://born2code.net/?page_id=45) that supports LocalService and NetworkService logons.
        /// Note: To use these built-in logons the code must be running under the local system account.
        /// </summary>
        public class Impersonation : IDisposable
        {
 
            #region Dll Imports
            /// <summary>
            /// Closes an open object handle.
            /// </summary>
            /// <param name="hObject">A handle to an open object.</param>
            /// <returns><c>True</c> when succeeded; otherwise <c>false</c>.</returns>
            [DllImport("kernel32.dll")]
            private static extern Boolean CloseHandle(IntPtr hObject);
 
            /// <summary>
            /// Attempts to log a user on to the local computer.
            /// </summary>
            /// <param name="username">This is the name of the user account to log on to. 
            /// If you use the user principal name (UPN) format, user@DNSdomainname, the 
            /// domain parameter must be <c>null</c>.</param>
            /// <param name="domain">Specifies the name of the domain or server whose 
            /// account database contains the lpszUsername account. If this parameter 
            /// is <c>null</c>, the user name must be specified in UPN format. If this 
            /// parameter is ".", the function validates the account by using only the 
            /// local account database.</param>
            /// <param name="password">The password</param>
            /// <param name="logonType">The logon type</param>
            /// <param name="logonProvider">The logon provides</param>
            /// <param name="userToken">The out parameter that will contain the user 
            /// token when method succeeds.</param>
            /// <returns><c>True</c> when succeeded; otherwise <c>false</c>.</returns>
            [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
            private static extern bool LogonUser(string username, string domain,
                                                  string password, LogonType logonType,
                                                  LogonProvider logonProvider,
                                                  out IntPtr userToken);
 
            /// <summary>
            /// Creates a new access token that duplicates one already in existence.
            /// </summary>
            /// <param name="token">Handle to an access token.</param>
            /// <param name="impersonationLevel">The impersonation level.</param>
            /// <param name="duplication">Reference to the token to duplicate.</param>
            /// <returns></returns>
            [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
            private static extern bool DuplicateToken(IntPtr token, int impersonationLevel,
                ref IntPtr duplication);
 
            /// <summary>
            /// The ImpersonateLoggedOnUser function lets the calling thread impersonate the 
            /// security context of a logged-on user. The user is represented by a token handle.
            /// </summary>
            /// <param name="userToken">Handle to a primary or impersonation access token that represents a logged-on user.</param>
            /// <returns>If the function succeeds, the return value is nonzero.</returns>
            [DllImport("advapi32.dll", SetLastError = true)]
            static extern bool ImpersonateLoggedOnUser(IntPtr userToken);
            #endregion
 
            #region Private members
            /// <summary>
            /// <c>true</c> if disposed; otherwise, <c>false</c>.
            /// </summary>
            private bool _disposed;
 
            /// <summary>
            /// Holds the created impersonation context and will be used
            /// for reverting to previous user.
            /// </summary>
            private WindowsImpersonationContext _impersonationContext;
            #endregion
 
            #region Ctor & Dtor
 
            /// <summary>
            /// Initializes a new instance of the <see cref="Impersonation"/> class and
            /// impersonates as a built in service account.
            /// </summary>
            /// <param name="builtinUser">The built in user to impersonate - either
            /// Local Service or Network Service. These users can only be impersonated
            /// by code running as System.</param>
            public Impersonation(BuiltinUser builtinUser)
                : this(String.Empty, "NT AUTHORITY", String.Empty, LogonType.Service, builtinUser)
            {
            }
 
            /// <summary>
            /// Initializes a new instance of the <see cref="Impersonation"/> class and
            /// impersonates with the specified credentials.
            /// </summary>
            /// <param name="username">his is the name of the user account to log on 
            /// to. If you use the user principal name (UPN) format, 
            /// user@DNS_domain_name, the lpszDomain parameter must be <c>null</c>.</param>
            /// <param name="domain">The name of the domain or server whose account 
            /// database contains the lpszUsername account. If this parameter is 
            /// <c>null</c>, the user name must be specified in UPN format. If this 
            /// parameter is ".", the function validates the account by using only the 
            /// local account database.</param>
            /// <param name="password">The plaintext password for the user account.</param>
            public Impersonation(String username, String domain, String password)
                : this(username, domain, password, LogonType.Interactive, BuiltinUser.None)
            {
            }
 
            private Impersonation(String username, String domain, String password, LogonType logonType, BuiltinUser builtinUser)
            {
                switch (builtinUser)
                {
                    case BuiltinUser.None: if (String.IsNullOrEmpty(username)) return; break;
                    case BuiltinUser.LocalService: username = "LOCAL SERVICE"; break;
                    case BuiltinUser.NetworkService: username = "NETWORK SERVICE"; break;
                }
 
                IntPtr userToken = IntPtr.Zero;
                IntPtr userTokenDuplication = IntPtr.Zero;
 
                // Logon with user and get token.
                bool loggedOn = LogonUser(username, domain, password,
                    logonType, LogonProvider.Default,
                    out userToken);
 
                if (loggedOn)
                {
                    try
                    {
                        // Create a duplication of the usertoken, this is a solution
                        // for the known bug that is published under KB article Q319615.
                        if (DuplicateToken(userToken, 2, ref userTokenDuplication))
                        {
                            // Create windows identity from the token and impersonate the user.
                            WindowsIdentity identity = new WindowsIdentity(userTokenDuplication);
                            _impersonationContext = identity.Impersonate();
                        }
                        else
                        {
                            // Token duplication failed!
                            // Use the default ctor overload
                            // that will use Mashal.GetLastWin32Error();
                            // to create the exceptions details.
                            throw new Win32Exception();
                        }
                    }
                    finally
                    {
                        // Close usertoken handle duplication when created.
                        if (!userTokenDuplication.Equals(IntPtr.Zero))
                        {
                            // Closes the handle of the user.
                            CloseHandle(userTokenDuplication);
                            userTokenDuplication = IntPtr.Zero;
                        }
 
                        // Close usertoken handle when created.
                        if (!userToken.Equals(IntPtr.Zero))
                        {
                            // Closes the handle of the user.
                            CloseHandle(userToken);
                            userToken = IntPtr.Zero;
                        }
                    }
                }
                else
                {
                    // Logon failed!
                    // Use the default ctor overload that 
                    // will use Mashal.GetLastWin32Error();
                    // to create the exceptions details.
                    throw new Win32Exception();
                }
            }
 
            /// <summary>
            /// Releases unmanaged resources and performs other cleanup operations before the
            /// <see cref="Born2Code.Net.Impersonation"/> is reclaimed by garbage collection.
            /// </summary>
            ~Impersonation()
            {
                Dispose(false);
            }
            #endregion
 
            #region Public methods
            /// <summary>
            /// Reverts to the previous user.
            /// </summary>
            public void Revert()
            {
                if (_impersonationContext != null)
                {
                    // Revert to previour user.
                    _impersonationContext.Undo();
                    _impersonationContext = null;
                }
            }
            #endregion
 
            #region IDisposable implementation.
            /// <summary>
            /// Performs application-defined tasks associated with freeing, releasing, or
            /// resetting unmanaged resources and will revent to the previous user when
            /// the impersonation still exists.
            /// </summary>
            public void Dispose()
            {
                Dispose(true);
                GC.SuppressFinalize(this);
            }
 
            /// <summary>
            /// Performs application-defined tasks associated with freeing, releasing, or
            /// resetting unmanaged resources and will revent to the previous user when
            /// the impersonation still exists.
            /// </summary>
            /// <param name="disposing">Specify <c>true</c> when calling the method directly
            /// or indirectly by a user’s code; Otherwise <c>false</c>.
            protected virtual void Dispose(bool disposing)
            {
                if (!_disposed)
                {
                    Revert();
 
                    _disposed = true;
                }
            }
            #endregion
        }
 
        #region Enums
 
        public enum LogonType : int
        {
            /// <summary>
            /// This logon type is intended for users who will be interactively using the computer, such as a user being logged on  
            /// by a terminal server, remote shell, or similar process.
            /// This logon type has the additional expense of caching logon information for disconnected operations;
            /// therefore, it is inappropriate for some client/server applications,
            /// such as a mail server.
            /// </summary>
            Interactive = 2,
 
            /// <summary>
            /// This logon type is intended for high performance servers to authenticate plaintext passwords.
            /// The LogonUser function does not cache credentials for this logon type.
            /// </summary>
            Network = 3,
 
            /// <summary>
            /// This logon type is intended for batch servers, where processes may be executing on behalf of a user without
            /// their direct intervention. This type is also for higher performance servers that process many plaintext
            /// authentication attempts at a time, such as mail or Web servers.
            /// The LogonUser function does not cache credentials for this logon type.
            /// </summary>
            Batch = 4,
 
            /// <summary>
            /// Indicates a service-type logon. The account provided must have the service privilege enabled.
            /// </summary>
            Service = 5,
 
            /// <summary>
            /// This logon type is for GINA DLLs that log on users who will be interactively using the computer.
            /// This logon type can generate a unique audit record that shows when the workstation was unlocked.
            /// </summary>
            Unlock = 7,
 
            /// <summary>
            /// This logon type preserves the name and password in the authentication package, which allows the server to make
            /// connections to other network servers while impersonating the client. A server can accept plaintext credentials
            /// from a client, call LogonUser, verify that the user can access the system across the network, and still
            /// communicate with other servers.
            /// NOTE: Windows NT:  This value is not supported.
            /// </summary>
            NetworkCleartText = 8,
 
            /// <summary>
            /// This logon type allows the caller to clone its current token and specify new credentials for outbound connections.
            /// The new logon session has the same local identifier but uses different credentials for other network connections.
            /// NOTE: This logon type is supported only by the LOGON32_PROVIDER_WINNT50 logon provider.
            /// NOTE: Windows NT:  This value is not supported.
            /// </summary>
            NewCredentials = 9,
        }
 
        public enum LogonProvider : int
        {
            /// <summary>
            /// Use the standard logon provider for the system.
            /// The default security provider is negotiate, unless you pass NULL for the domain name and the user name
            /// is not in UPN format. In this case, the default provider is NTLM.
            /// NOTE: Windows 2000/NT:   The default security provider is NTLM.
            /// </summary>
            Default = 0,
        }
 
        public enum BuiltinUser
        {
            None,
            LocalService,
            NetworkService
        }
 
        #endregion
 
    }
}

13 comments:

DethKnite said...

This is exactly what I am looking for. I need to shell out and run an application/cmd under the "SYSTEM" user context.

If possible, could you provide an example of the impersonation class in use.

ie. ... = new() etc.

Thanks!

Caley

txs8311 said...

Check out the static void Main(string[] args) entry point above - it gives an example of the impersonation class in use.

DethKnite said...

Hmmm, I am not able to impersonate the LocalSystem account... "don't have the permissions". Although I am a local admin on the PC, I can't get it to impersonate "SYSTEM".

//code start----->

MessageBox.Show(WindowsIdentity.GetCurrent().Name);
using (Impersonation imp = new Impersonation(BuiltinUser.LocalService))
{
MessageBox.Show(WindowsIdentity.GetCurrent().Name);
}

MessageBox.Show("done");


//code end----->

Any ideas...

txs8311 said...

Huh. The only thing I can think of is that the console window that opened after you ran

C:\sc start testsvc

is not running as SYSTEM.

Try typing this into that console window:

C:\WINDOWS\system32>net config workstation

You should get an error like:

A specified logon session does not exist.

If you don't get an error (you'll see a listing that includes your user name) - try recreating the server and starting it.

If you do get an error, navigate to your .exe folder in the console window and run your assembly. If you've got System.Diagnostics.Debugger.Break() set, you should be able to break into the code to debug.

DethKnite said...

Figured it out, I am a local admin of the local pc, but I am logging on with a domain account and I am setup as a domain user with the account. There is also a Deny policy on the local machine that has Users on it.

seoer said...

Hi,

I'm facing out with a problem. Should read the Http 404 errors in IIS and I though your code was able to let impersonate the running anonymous user a Network service that can read that informations.
But I get denied access. Have you a particular idea?

David Perry said...

I want to execute my console app from a Classic ASP page using WScript. The IIS website runs under network service, but I need the console app to run as local system. How do I get the CMD.exe test service to run my console app, without requiring user intervention?

Anonymous said...

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Sorry for offtopic

John Cheng said...

I get error when trying to start the service.

[SC] StartService FAILED 1053:

The service did not respond to the start or control request in a timely fashion.

Anonymous said...

-- John Cheng
>> [SC] StartService FAILED 1053:

I had the same problem when I ran the example in the post on a machine to which I was connected by RDP.

The example worked as described when I ran it on my local machine.

Anonymous said...

Nice article!
I tried using this code for attempting to impersonate LocalSystem but with no success...
username was "SYSTEM", domain "NT AUTHORITY", empty password, Interactive LogonType, and Default LogonProvider.
But when calling LogonUser, i get the exception:
"Logon Failure: unknown user name or bad password. (Exception from HRESULT: 0x8007052E)"
Any ideas why this is happening? I run it as LocalSystem by the way...

nmasxkasx said...

Very Nice article!
I tried using this code
from a console application as shown in the example but it failed

.......
using (Impersonation imp = new Impersonation(BuiltinUser.LocalService))
{
Console.WriteLine(WindowsIdentity.GetCurrent().Name);
}
......


Exception

System.ComponentModel.Win32Exception: Access is denied
at DevHoleDemo.Program.Impersonation..ctor(String username, String domain, St
ring password, LogonType logonType, BuiltinUser builtinUser) in C:\comp\C
onsoleApplication9\ConsoleApplication9\Program.cs:line 214
at DevHoleDemo.Program.Impersonation..ctor(BuiltinUser builtinUser) in C:\comp\ConsoleApplication9\ConsoleApplication9\Program.cs:line 122
at DevHoleDemo.Program.Main(String[] args) in C:\comp\ConsoleApplication9\ConsoleApplication9\Program.cs:line 24

Can you please guide me what can be wrong here...

JC`zic said...

Just note that the domain or username strings (NT AUTHORITY, NETWORK SERVICE) works only on a US Windows version.

A good way to seek valid strings is to use System.Security.Principal.WellKnownSidType.(NetworkServiceSid, ...)