launch process from Session 0 Isolation

Question

On Windows 8.1 I have a service that starts PowerShell scripts. The service runs as “nt authority\system” in Session 0 Isolation. Any process that I spawn from PowerShell runs as “nt authority\system” in Session 0 Isolation.

I need to run a script that is under a user account out of session 0 and not the system account. I have tried this

Start-Process "$PsHome\PowerShell.exe" -Credential $pp -ArgumentList $script  -wait 

and PsExec specifying which session I want with "-I 1" argument.

& PsExec.exe "Install.bat" -i 1 -accepteula -u "domain\user" -p "awesomePassword" -w "startdir" -h

I have tried setting "Allow service to interact with desktop".

I keep getting Access is denied errors when I try and start the process either from PowerShell or from the c# service.

Here is an example exception when I try to escape using c# on the service.

System.ComponentModel.Win32Exception (0x80004005): Access is denied
   at System.Diagnostics.Process.StartWithCreateProcess(ProcessStartInfo startInfo)

How do I escape from session 0?

I can re-write the c# code to start a process under a different user. or I can re-write the called PowerShell script to start another process as a user. No matter what I try, I can't seem to break out of session 0.

Answer 1

Using the example I found at code project I got a partial solution. The example in the link above will launch a process as the user who is running the "winlogon" process. In order to launch a process as the user who is logged in I just changed the process to look for "explorer" instead.

Here is a snippet of the original code

// obtain the process id of the winlogon process that is 
// running within the currently active session
Process[] processes = Process.GetProcessesByName("winlogon");

I just change the process to look for explorer.

Process[] processes = Process.GetProcessesByName("explorer");

Now the process launches as domain/me in Session 3 as a user not admin.

There has to be issues with this approach, such as Remote Desktop, but for what I want this will ultimately do.

Here is the final code for completeness in case the original link evaporates.

Here is how to launch it

// the name of the application to launch
String applicationName = "cmd.exe";

// launch the application
ApplicationLoader.PROCESS_INFORMATION procInfo;
ApplicationLoader.StartProcessAndBypassUAC(applicationName, out procInfo);

Here is the code

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Security;

namespace SuperAwesomeNameSpaceOfJustice
{
    /// <summary>
    /// Class that allows running applications with full admin rights. In
    /// addition the application launched will bypass the Vista UAC prompt.
    /// </summary>
    public class ApplicationLoader
    {
        #region Structures

        [StructLayout(LayoutKind.Sequential)]
        public struct SECURITY_ATTRIBUTES
        {
            public int Length;
            public IntPtr lpSecurityDescriptor;
            public bool bInheritHandle;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct STARTUPINFO
        {
            public int cb;
            public String lpReserved;
            public String lpDesktop;
            public String lpTitle;
            public uint dwX;
            public uint dwY;
            public uint dwXSize;
            public uint dwYSize;
            public uint dwXCountChars;
            public uint dwYCountChars;
            public uint dwFillAttribute;
            public uint dwFlags;
            public short wShowWindow;
            public short cbReserved2;
            public IntPtr lpReserved2;
            public IntPtr hStdInput;
            public IntPtr hStdOutput;
            public IntPtr hStdError;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct PROCESS_INFORMATION
        {
            public IntPtr hProcess;
            public IntPtr hThread;
            public uint dwProcessId;
            public uint dwThreadId;
        }

        #endregion

        #region Enumerations

        enum TOKEN_TYPE : int
        {
            TokenPrimary = 1,
            TokenImpersonation = 2
        }

        enum SECURITY_IMPERSONATION_LEVEL : int
        {
            SecurityAnonymous = 0,
            SecurityIdentification = 1,
            SecurityImpersonation = 2,
            SecurityDelegation = 3,
        }

        #endregion

        #region Constants

        public const int TOKEN_DUPLICATE = 0x0002;
        public const uint MAXIMUM_ALLOWED = 0x2000000;
        public const int CREATE_NEW_CONSOLE = 0x00000010;

        public const int IDLE_PRIORITY_CLASS = 0x40;
        public const int NORMAL_PRIORITY_CLASS = 0x20;
        public const int HIGH_PRIORITY_CLASS = 0x80;
        public const int REALTIME_PRIORITY_CLASS = 0x100;

        #endregion

        #region Win32 API Imports

        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern bool CloseHandle(IntPtr hSnapshot);

        [DllImport("kernel32.dll")]
        static extern uint WTSGetActiveConsoleSessionId();

        [DllImport("advapi32.dll", EntryPoint = "CreateProcessAsUser", SetLastError = true, CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
        public extern static bool CreateProcessAsUser(IntPtr hToken, String lpApplicationName, String lpCommandLine, ref SECURITY_ATTRIBUTES lpProcessAttributes,
            ref SECURITY_ATTRIBUTES lpThreadAttributes, bool bInheritHandle, int dwCreationFlags, IntPtr lpEnvironment,
            String lpCurrentDirectory, ref STARTUPINFO lpStartupInfo, out PROCESS_INFORMATION lpProcessInformation);

        [DllImport("kernel32.dll")]
        static extern bool ProcessIdToSessionId(uint dwProcessId, ref uint pSessionId);

        [DllImport("advapi32.dll", EntryPoint = "DuplicateTokenEx")]
        public extern static bool DuplicateTokenEx(IntPtr ExistingTokenHandle, uint dwDesiredAccess,
            ref SECURITY_ATTRIBUTES lpThreadAttributes, int TokenType,
            int ImpersonationLevel, ref IntPtr DuplicateTokenHandle);

        [DllImport("kernel32.dll")]
        static extern IntPtr OpenProcess(uint dwDesiredAccess, bool bInheritHandle, uint dwProcessId);

        [DllImport("advapi32", SetLastError = true), SuppressUnmanagedCodeSecurity]
        static extern bool OpenProcessToken(IntPtr ProcessHandle, int DesiredAccess, ref IntPtr TokenHandle);

        #endregion

        /// <summary>
        /// Launches the given application with full admin rights, and in addition bypasses the Vista UAC prompt
        /// </summary>
        /// <param name="applicationName">The name of the application to launch</param>
        /// <param name="procInfo">Process information regarding the launched application that gets returned to the caller</param>
        /// <returns></returns>
        public static bool StartProcessAndBypassUAC(String applicationName, string startingDir, out PROCESS_INFORMATION procInfo)
        {
            uint winlogonPid = 0;
            IntPtr hUserTokenDup = IntPtr.Zero, hPToken = IntPtr.Zero, hProcess = IntPtr.Zero;
            procInfo = new PROCESS_INFORMATION();

            // obtain the currently active session id; every logged on user in the system has a unique session id
            uint dwSessionId = WTSGetActiveConsoleSessionId();

            // obtain the process id of the winlogon process that is running within the currently active session
            // -- chaged by ty 
            // Process[] processes = Process.GetProcessesByName("winlogon");
            Process[] processes = Process.GetProcessesByName("explorer");
            foreach (Process p in processes)
            {
                if ((uint)p.SessionId == dwSessionId)
                {
                    winlogonPid = (uint)p.Id;
                }
            }

            // obtain a handle to the winlogon process
            hProcess = OpenProcess(MAXIMUM_ALLOWED, false, winlogonPid);

            // obtain a handle to the access token of the winlogon process
            if (!OpenProcessToken(hProcess, TOKEN_DUPLICATE, ref hPToken))
            {
                CloseHandle(hProcess);
                return false;
            }

            // Security attibute structure used in DuplicateTokenEx and CreateProcessAsUser
            // I would prefer to not have to use a security attribute variable and to just 
            // simply pass null and inherit (by default) the security attributes
            // of the existing token. However, in C# structures are value types and therefore
            // cannot be assigned the null value.
            SECURITY_ATTRIBUTES sa = new SECURITY_ATTRIBUTES();
            sa.Length = Marshal.SizeOf(sa);

            // copy the access token of the winlogon process; the newly created token will be a primary token
            if (!DuplicateTokenEx(hPToken, MAXIMUM_ALLOWED, ref sa, (int)SECURITY_IMPERSONATION_LEVEL.SecurityIdentification, (int)TOKEN_TYPE.TokenPrimary, ref hUserTokenDup))
            {
                CloseHandle(hProcess);
                CloseHandle(hPToken);
                return false;
            }

            // By default CreateProcessAsUser creates a process on a non-interactive window station, meaning
            // the window station has a desktop that is invisible and the process is incapable of receiving
            // user input. To remedy this we set the lpDesktop parameter to indicate we want to enable user 
            // interaction with the new process.
            STARTUPINFO si = new STARTUPINFO();
            si.cb = (int)Marshal.SizeOf(si);
            si.lpDesktop = @"winsta0\default"; // interactive window station parameter; basically this indicates that the process created can display a GUI on the desktop

            // flags that specify the priority and creation method of the process
            int dwCreationFlags = NORMAL_PRIORITY_CLASS | CREATE_NEW_CONSOLE;

            // create a new process in the current user's logon session
            bool result = CreateProcessAsUser(hUserTokenDup,        // client's access token
                                            null,                   // file to execute
                                            applicationName,        // command line
                                            ref sa,                 // pointer to process SECURITY_ATTRIBUTES
                                            ref sa,                 // pointer to thread SECURITY_ATTRIBUTES
                                            false,                  // handles are not inheritable
                                            dwCreationFlags,        // creation flags
                                            IntPtr.Zero,            // pointer to new environment block 
                                            startingDir,                   // name of current directory 
                                            ref si,                 // pointer to STARTUPINFO structure
                                            out procInfo            // receives information about new process
                                            );

            // invalidate the handles
            CloseHandle(hProcess);
            CloseHandle(hPToken);
            CloseHandle(hUserTokenDup);

            return result; // return the result
        }

    }
}