A complete Impersonation Demo in C#.NET

Under some scenarios we need impersonate another Windows account and do some work under that user’s session, for example:

  • An enterprise ASP.NET web application provides server administrators’ ability to access the server under some specific privilege set; Server admin input their NT account information (domain\account + password) on the page, we need get WinNT Access Token and then impersonate this server user, so that we acquire its specific privilege and do the things ONLY THIS ACCOUNT CAN DO.
  • We developed a Windows Service which needs internet access periodically, but a specific user sets an Sock5 proxy to access internet, then your Windows Service needs to know the Socks proxy information so that it could access internet, you must impersonate this user and read the settings.
  • Impersonation definition

    Definition copied from: http://msdn.microsoft.com/en-us/library/aa376391(VS.85).aspx

    Impersonation is the ability of a thread to execute using different security information than the process that owns the thread. Typically, a thread in a server application impersonates a client. This allows the server thread to act on behalf of that client to access objects on the server or validate access to the client’s own objects.

    I read many articles and blogs and wrote an ImpersonateHelper class to do impersonation work, during the investigating I noticed that very few articles/blogs refer a complete impersonation process, so I decided to write one that refer as more details as I can, and actually my code was a code snippet combination came from 10+ sourcesSmile.

    Functionality

    I create a local user: TempUser which belongs to “Administrators” (make sure log on TempUser at least once), I logged on as my own account and I am going to impersonate TempUser and do two things:

    1. Create a folder “C:\TempFolder”, modify its default privilege, ONLY TempUser has full control of it, I will create a text file under this folder after impersonating to prove impersonation is successfully.
      Tempfolder1Notes: After setting TempUser as the only owner, my current account cannot access this folder except privilege promotion (I disabled UAC, if UAC is enabled, a prompt window will pop up and as for Admin confirm).
      Tempfolder2 

      In additional, I tried to access this folder programmatically under my account, UnauthorizedAccessException will be thrown!

      Unauthorized

    2. I will access TempUser’s HKEY_CURRENT_USER and do registry key creation, reading and deleting.

    Code Snippet

    We need invoke three very famous Win32 API: LogonUser, DuplicateToken and RevertToSelf.

            [DllImport("advapi32.dll")]
            public static extern int LogonUser(String lpszUserName,
                String lpszDomain,
                String lpszPassword,
                int dwLogonType,
                int dwLogonProvider,
                ref IntPtr phToken);
    
            [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
            public static extern int DuplicateToken(IntPtr hToken, int impersonationLevel, ref IntPtr hNewToken);
    
            ///
            /// A process should call the RevertToSelf function after finishing any impersonation begun by using the DdeImpersonateClient, ImpersonateDdeClientWindow, ImpersonateLoggedOnUser, ImpersonateNamedPipeClient, ImpersonateSelf, ImpersonateAnonymousToken or SetThreadToken function.
            /// If RevertToSelf fails, your application continues to run in the context of the client, which is not appropriate. You should shut down the process if RevertToSelf fails.
            /// RevertToSelf Function: http://msdn.microsoft.com/en-us/library/aa379317(VS.85).aspx
            ///
            /// A boolean value indicates the function succeeded or not.
            [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
            public static extern bool RevertToSelf();
    
            [DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
            public static extern bool CloseHandle(IntPtr handle);
    

    An important notes: in order to access HKCU, we need invoke another Win32 API: LoadUserProfile, to acquire the handle of HKCU under TempUser, code below, as I highlighted line 45 and 49, after invoking LoadUserProfile, hProfile will be set handle to HKCU:

        [StructLayout(LayoutKind.Sequential)]
        public struct ProfileInfo
        {
            ///
            /// Specifies the size of the structure, in bytes.
            ///
            public int dwSize;
    
            ///
            /// This member can be one of the following flags: PI_NOUI or PI_APPLYPOLICY
            ///
            public int dwFlags;
    
            ///
            /// Pointer to the name of the user.
            /// This member is used as the base name of the directory in which to store a new profile.
            ///
            public string lpUserName;
    
            ///
            /// Pointer to the roaming user profile path.
            /// If the user does not have a roaming profile, this member can be NULL.
            ///
            public string lpProfilePath;
    
            ///
            /// Pointer to the default user profile path. This member can be NULL.
            ///
            public string lpDefaultPath;
    
            ///
            /// Pointer to the name of the validating domain controller, in NetBIOS format.
            /// If this member is NULL, the Windows NT 4.0-style policy will not be applied.
            ///
            public string lpServerName;
    
            ///
            /// Pointer to the path of the Windows NT 4.0-style policy file. This member can be NULL.
            ///
            public string lpPolicyPath;
    
            ///
            /// Handle to the HKEY_CURRENT_USER registry key.
            ///
            public IntPtr hProfile;
        }
    
            [DllImport("userenv.dll", SetLastError = true, CharSet = CharSet.Auto)]
            public static extern bool LoadUserProfile(IntPtr hToken, ref ProfileInfo lpProfileInfo);
    
            [DllImport("Userenv.dll", CallingConvention = CallingConvention.Winapi, SetLastError = true, CharSet = CharSet.Auto)]
            public static extern bool UnloadUserProfile(IntPtr hToken, IntPtr lpProfileInfo);
    

    Code to execute impersonation:

    WindowsIdentity m_ImpersonatedUser;
                IntPtr token = IntPtr.Zero;
                IntPtr tokenDuplicate = IntPtr.Zero;
                const int SecurityImpersonation = 2;
                const int TokenType = 1;
    
                try
                {
                    if (RevertToSelf())
                    {
                        Console.WriteLine("Before impersonation: " +
                                          WindowsIdentity.GetCurrent().Name);
    
                        String userName = "TempUser";
                        IntPtr password = GetPassword();
    
                        if (LogonUser(userName, Environment.MachineName, "!@#$QWERasdf", LOGON32_LOGON_INTERACTIVE,
                                      LOGON32_PROVIDER_DEFAULT, ref token) != 0)
                        {
                            if (DuplicateToken(token, SecurityImpersonation, ref tokenDuplicate) != 0)
                            {
                                m_ImpersonatedUser = new WindowsIdentity(tokenDuplicate);
                                using (m_ImpersonationContext = m_ImpersonatedUser.Impersonate())
                                {
                                    if (m_ImpersonationContext != null)
                                    {
                                        Console.WriteLine("After Impersonation succeeded: " + Environment.NewLine +
                                                          "User Name: " +
                                                          WindowsIdentity.GetCurrent(TokenAccessLevels.MaximumAllowed).Name +
                                                          Environment.NewLine +
                                                          "SID: " +
                                                          WindowsIdentity.GetCurrent(TokenAccessLevels.MaximumAllowed).User.
                                                              Value);
    
                                        #region LoadUserProfile
                                        // Load user profile
                                        ProfileInfo profileInfo = new ProfileInfo();
                                        profileInfo.dwSize = Marshal.SizeOf(profileInfo);
                                        profileInfo.lpUserName = userName;
                                        profileInfo.dwFlags = 1;
                                        Boolean loadSuccess = LoadUserProfile(tokenDuplicate, ref profileInfo);
    
                                        if (!loadSuccess)
                                        {
                                            Console.WriteLine("LoadUserProfile() failed with error code: " +
                                                              Marshal.GetLastWin32Error());
                                            throw new Win32Exception(Marshal.GetLastWin32Error());
                                        }
    
                                        if (profileInfo.hProfile == IntPtr.Zero)
                                        {
                                            Console.WriteLine(
                                                "LoadUserProfile() failed - HKCU handle was not loaded. Error code: " +
                                                Marshal.GetLastWin32Error());
                                            throw new Win32Exception(Marshal.GetLastWin32Error());
                                        }
                                        #endregion
    
                                        CloseHandle(token);
                                        CloseHandle(tokenDuplicate);
    
                                        // Do tasks after impersonating successfully
                                        AccessFileSystem();
    
                                        // Access HKCU after loading user's profile
                                        AccessHkcuRegistry(profileInfo.hProfile);
    
                                        // Unload user profile
                                        // MSDN remarks http://msdn.microsoft.com/en-us/library/bb762282(VS.85).aspx
                                        // Before calling UnloadUserProfile you should ensure that all handles to keys that you have opened in the
                                        // user's registry hive are closed. If you do not close all open registry handles, the user's profile fails
                                        // to unload. For more information, see Registry Key Security and Access Rights and Registry Hives.
                                        UnloadUserProfile(tokenDuplicate, profileInfo.hProfile);
    
                                        // Undo impersonation
                                        m_ImpersonationContext.Undo();
                                    }
                                }
                            }
                            else
                            {
                                Console.WriteLine("DuplicateToken() failed with error code: " + Marshal.GetLastWin32Error());
                                throw new Win32Exception(Marshal.GetLastWin32Error());
                            }
                        }
                    }
                }
                catch (Win32Exception we)
                {
                    throw we;
                }
                catch
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
                finally
                {
                    if (token != IntPtr.Zero) CloseHandle(token);
                    if (tokenDuplicate != IntPtr.Zero) CloseHandle(tokenDuplicate);
    
                    Console.WriteLine("After finished impersonation: " + WindowsIdentity.GetCurrent().Name);
                }
    

    AccessFileSystem method

            private static void AccessFileSystem()
            {
                // Access file system %appdata% will be "C:\Users\TempUser\appdata\Roaming"
                String appDataPath = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);
                File.AppendAllText("C:\\TempFolder\\Temp.txt", "some text...");
            }
    

    AccessHkcuRegistry method

            private static void AccessHkcuRegistry(IntPtr hkcuHandle)
            {
                // Access registry HKCU
                using (SafeRegistryHandle safeHandle = new SafeRegistryHandle(hkcuHandle, true))
                {
                    using (RegistryKey tempUserHKCU = RegistryKey.FromHandle(safeHandle))
                    {
                        // Unum all sub keys under tempuser's HKCU
                        String[] keys = tempUserHKCU.GetSubKeyNames();
    
                        // Create a new sub key under tempuser's HKCU
                        using (RegistryKey tempKeyByWayne = tempUserHKCU.CreateSubKey("TempKeyByWayne"))
                        {
                            // Ensure priviledge
                            //RegistrySecurity registrySecurity = new RegistrySecurity();
                            //RegistryAccessRule accessRule = new RegistryAccessRule(Environment.MachineName + "\\" + userName,
                            //                                                       RegistryRights.TakeOwnership,
                            //                                                       InheritanceFlags.ContainerInherit,
                            //                                                       PropagationFlags.None,
                            //                                                       AccessControlType.Allow);
                            //registrySecurity.SetAccessRule(accessRule);
                            //tempKeyByWayne.SetAccessControl(registrySecurity);
    
                            // Create a new String value under created TempKeyByWayne subkey
                            tempKeyByWayne.SetValue("StrType", "TempContent", RegistryValueKind.String);
    
                            // Read the value
                            using (RegistryKey regKey = tempUserHKCU.OpenSubKey("TempKeyByWayne"))
                            {
                                String valueContent = regKey.GetValue("StrType") as String;
                                Console.WriteLine(valueContent);
                            }
    
                            // Delete created TempKeyByWayne subkey
                            tempUserHKCU.DeleteSubKey("TempKeyByWayne");
                            tempKeyByWayne.Close();
                        }
                    }
                }
            }
    

    Impersonation result and verification

    Temp.txt was created.
    TempFolder

    “TempKeyByWayne” was created under HKCU.
    Registry

    Complete source code download

    References

    How to implement impersonation in an ASP.NET application
    http://support.microsoft.com/kb/306158

    LogonUser Win32 API
    http://msdn.microsoft.com/en-us/library/aa378184(VS.85).aspx

    How to spawn a process that runs under the context of the impersonated user in Microsoft ASP.NET pages
    http://support.microsoft.com/kb/889251

    ASP.NET Impersonation
    http://msdn.microsoft.com/en-us/library/xh507fc5(v=VS.100).aspx

    Safely Impersonating Another User
    http://blogs.msdn.com/b/shawnfa/archive/2005/03/22/400749.aspx

    Original post permalink: http://wayneye.com/Blog/DotNet-Impersonation-Demo

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    Programmatically PIN shortcut onto Taskbar on Win7

    During my work I got one requirement of pinning a specific shortcut file (*.lnk) onto the Windows 7 Taskbar, after investigating I found programmtically achive this is “not permitted”, refer MSDN article: http://msdn.microsoft.com/en-us/library/dd378460(VS.85).aspx

    A small set of applications are pinned by default for new installations. Other than these, only the user can pin further applications; programmatic pinning by an application is not permitted.

    However, the exception comes from Windows Script Hosting, a snippet of VBscript can achieve my requirement, I read several articles (refer the end of this post) and wrote two VBS scripts showing below:

    Pin to Taskbar

    Option Explicit
    
    'Const CSIDL_COMMON_PROGRAMS = &H17
    Dim ShellApp, FSO, Desktop
    Set ShellApp = CreateObject("Shell.Application")
    Set FSO = CreateObject("Scripting.FileSystemObject")
    
    'Set StartMenuFolder = ShellApp.NameSpace(CSIDL_COMMON_PROGRAMS)
    Set Desktop =  ShellApp.NameSpace("C:\Users\Wayne\Desktop")
    
    Dim LnkFile
    LnkFile = Desktop.Self.Path&"\ScheduleNotifier.lnk"
    
    If(FSO.FileExists(LnkFile)) Then
    	Dim tmp, verb
    	'For Each verb in Desktop.ParseName("ScheduleNotifier.lnk").Verbs
    		'tmp = tmp&verb&chr(13)
    	'Next
    	'MsgBox(tmp)
    
    	Dim desktopImtes, item
    	Set desktopImtes = Desktop.Items()
    
    	For Each item in desktopImtes
    		If (item.Name = "ScheduleNotifier") Then
    			'MsgBox(item.Name)
    			For Each verb in item.Verbs
    				If (verb.Name = "Pin to Tas&kbar") Then 'If (verb.Name = "锁定到任务栏(&K)")
    					verb.DoIt
    				End If
    			Next
    		End If
    	Next
    
    End If
    
    Set FSO = Nothing
    Set ShellApp = Nothing
    

    Unpin from Taskbar

    Option Explicit
    'Const CSIDL_COMMON_PROGRAMS = &H17
    Dim ShellApp, FSO, Desktop
    Set ShellApp = CreateObject("Shell.Application")
    Set FSO = CreateObject("Scripting.FileSystemObject")
    
    'Set StartMenuFolder = ShellApp.NameSpace(CSIDL_COMMON_PROGRAMS)
    Set Desktop =  ShellApp.NameSpace("C:\Users\Wayne\Desktop")
    
    Dim LnkFile
    LnkFile = Desktop.Self.Path&"\ScheduleNotifier.lnk"
    
    If(FSO.FileExists(LnkFile)) Then
    	Dim tmp, verb
    	'For Each verb in Desktop.ParseName("ScheduleNotifier.lnk").Verbs
    		'tmp = tmp&verb&chr(13)
    	'Next
    	'MsgBox(tmp)
    
    	Dim desktopImtes, item
    	Set desktopImtes = Desktop.Items()
    
    	For Each item in desktopImtes
    		If (item.Name = "ScheduleNotifier") Then
    			'MsgBox(item.Name)
    			For Each verb in item.Verbs
    				If (verb.Name = "Unpin from Tas&kbar") Then 'If (verb.Name = "从任务栏脱离(&K)")
    					verb.DoIt
    				End If
    			Next
    		End If
    	Next
    
    End If
    
    Set FSO = Nothing
    Set ShellApp = Nothing
    

    Although two snippets of VBS code are simple and stright-forward, they has on serious limitation, it only support one specified language, attention of this line of code:

    If (verb.Name = "Pin to Tas&kbar") Then 'If (verb.Name = "锁定到任务栏(&K)")
    

    On Chinese locale, I have to replace “Pin to Tas&kbar” with “锁定到任务栏(&K)”, so in order to support more languages I need to know each exact {Pin sentence} to do the pinning, you know, google translation won’t always work in this case:), so I definitely don’t want to do that…

     

    You probably ask WHY??? Because FolderItemVerb object only has one property: Name, and Name is definitely “language sensitive“, MSDN does mention there are two more properties “Application” and “Parent” however they are “Not implemented”.

    Several tips

  • For a specific Windows user, all shortcuts pinned onto taskbar store the shortcuts files under
    %AppData%\Microsoft\Internet Explorer\Quick Launch\User Pinned\TaskBar
  • OEM manufacturers could “pre-pin” some shortcut onto the Taskbar before shipping the PC/laptops to the consumers, simply run batch command below during the DASH (see Desktop and mobile Architecture for System Hardware) process:
    Rem Pining OEM Welcome Center app on task barReg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\TBDEn /v SBOEM0 /t REG_EXPAND_SZ /d “SomeFile.lnk” /f
  •  

    References

    Pin and Un-pin items to/from the Windows 7 taskbar
    http://blog.ananthonline.net/?p=37

    Personal Schedule Management Tool

    Time is always ticking no matter you care it or you don’t care it, everyone knows it including myself, to remind myself don’t waste too much time on gaming, reading news or something else, I developed a little tool which I call it “Personal Schedule Management Tool” to achieve this simple goal.

    Mechanism

    I create an XML file to store a serial of [time stamp/task to do] pairs, the tool will start with Windows and load the XML file, a working timer behind it will periodically check whether there is a task needs to be done at defined time stamp, once the condition is matched, the tool will

    1. Shows Windows Balloon Tips with the task as content, screenshot below.
      Balloon
    2. Invokes managed Microsoft Speech API: SpeechSynthesizer.Speak() to remind me even if I am not in front of my dev-box at that time.

    Here is my XML to store schedule items:

    <?xml version="1.0" encoding="utf-8" ?>
    <WayneScheduleItems>
      <ScheduleItem TriggerHour="18" TriggerMinute="20" Content="Wayne, time to have your dinner." />
      <ScheduleItem TriggerHour="19" TriggerMinute="0" Content="Wayne! It is time to learn technologies and programming skills, i.e. CODING TIME!" />
      <ScheduleItem TriggerHour="20" TriggerMinute="30" Content="OK, your eye and brain need rest, time to do some body execise - running, sit-ups, push-up, etc.  Enjoy:)" />
      <ScheduleItem TriggerHour="21" TriggerMinute="0" Content="Well, sweat off your face and have a bath:)." />
      <ScheduleItem TriggerHour="21" TriggerMinute="30" Content="All right, well come back, you know you should read some books!" />
      <ScheduleItem TriggerHour="23" TriggerMinute="0" Content="Wayne, thanks for the hard work! Time to sleep, have a good night!" />
    </WayneScheduleItems>
    

    UI Implementation

    The tool is a WinForm developed in C#, it has no Windows and starts in system tray, to achieve this I set MainWindow’s FormBorderStyle = None, ShowIcon = False and ShowInTaskBar = False, see below.

    WindowProperty

    One more thing is drag two controls onto the form: System.Windows.Forms.NotifyIcon, System.Windows.Forms.ContextMenuStrip and  and naming the instances as “systrayIcon” and “systrayMenu”.

    Controls

    After that I need add menu items, code snippet below:

    this.editScheduleItemsToolStripMenuItem.Name = "editScheduleItemsToolStripMenuItem";
    this.editScheduleItemsToolStripMenuItem.Text = "Edit Schedule Items";
    this.editScheduleItemsToolStripMenuItem.Click += new System.EventHandler(this.editScheduleItemsToolStripMenuItem_Click);
    this.systrayMenu.Items.Add(editScheduleItemsToolStripMenuItem);
    

    All right, its appearance is like below:

    SystrayMenu

    Functionality implementation

    Timer:

                // Initializes timer
                scheduleTimer = new System.Timers.Timer()
                                {
                                    Interval = 1000d * 60 * 10, // 10 minutes
                                    Enabled = true
                                };
                this.scheduleTimer.Start();
                this.scheduleTimer.Elapsed += new System.Timers.ElapsedEventHandler(scheduleTimer_Elapsed);
            }
    
            void scheduleTimer_Elapsed(object sender, ElapsedEventArgs e)
            {
                DateTime currentTime = e.SignalTime;
    
                try
                {
                    foreach (ScheduleItem scheduleItem in scheduleItems)
                    {
                        if (currentTime.Hour == scheduleItem.TriggerHour
                        && currentTime.Minute == scheduleItem.TriggerMinute)
                        {
                            LogManager.WriteAsync(String.Format("{0}, notification occurred: {1}.{2}",
                                currentTime.ToLocalTime(), scheduleItem.Content, Environment.NewLine));
    
                            // Trigger bubble/voice notification
                            this.systrayIcon.ShowBalloonTip(8000, Constants.BalloonTitle, scheduleItem.Content, ToolTipIcon.Info);
                            SoundNotifier.Phonate(scheduleItem.Content);
    
                            break; // Avoid redundant check
                        }
                    }
                }
                catch (Exception ex)
                {
                    LogManager.WriteAsync(ex.Message);
                }
    
                LogManager.WriteAsync(String.Format("Schedule check at: {0}{1}", currentTime.ToLocalTime(), Environment.NewLine));
            }
    

    Load schedule items from XML using LINQ:

        public static class ScheduleItemsReader
        {
            private static readonly String ScheduleItemsXmlLocation = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "ScheduleItems.xml");
    
            public static IEnumerable<ScheduleItem> Load()
            {
                IList<ScheduleItem> scheduleItems = new List<ScheduleItem>();
    
                IEnumerable<XElement> scheduleItemsCollection = from scheduleItem in XElement.Load(ScheduleItemsXmlLocation).Descendants("ScheduleItem")
                                                                select scheduleItem;
    
                foreach (XElement ele in scheduleItemsCollection)
                {
                    ScheduleItem scheduleItem = new ScheduleItem();
                    scheduleItem.TriggerHour = ushort.Parse(ele.Attribute("TriggerHour").Value);
                    scheduleItem.TriggerMinute = ushort.Parse(ele.Attribute("TriggerMinute").Value);
                    scheduleItem.Content = ele.Attribute("Content").Value;
    
                    scheduleItems.Add(scheduleItem);
                }
    
                return scheduleItems;
            }
        }
    

    Invoke Speech API:

        public static class SoundNotifier
        {
            public static void Phonate(String sentence)
            {
                using (SpeechSynthesizer speaker = new SpeechSynthesizer())  // Dispose the its instance as soon as it spoke fnished
                {
                    ReadOnlyCollection<InstalledVoice> installedVoices = speaker.GetInstalledVoices();
    
                    CultureInfo cultureInfo = CultureInfo.GetCultureInfo("en-US");
    
                    PromptBuilder pb = new PromptBuilder();
                    pb.StartVoice(VoiceGender.Female, VoiceAge.Adult);
                    pb.StartStyle(new PromptStyle(PromptVolume.Loud));
    
                    pb.StartSentence();
                    pb.AppendText(sentence, PromptEmphasis.Strong);
                    pb.EndSentence();
    
                    pb.EndStyle();
                    pb.EndVoice();
    
                    speaker.Speak(pb);
                }
            }
        }
    

    LogManager:

            public static void WriteAsync(String content)
            {
                FileStream fileStream = null;
    
                LogFilePath = String.Format(LogFilePath, DateTime.Now.ToString("MM-dd-yyyy"));
                if (File.Exists(LogFilePath))
                    fileStream = File.OpenWrite(LogFilePath);
                else
                    fileStream = File.Create(LogFilePath);
                FileInfo logFile = new FileInfo(LogFilePath);
    
                StringBuilder logBuilder = new StringBuilder();
                logBuilder.AppendFormat(
                    "===================================================================================================={0}{1}{0}{0}",
                    Environment.NewLine,
                    content);
    
                byte[] data = Encoding.UTF8.GetBytes(logBuilder.ToString());
                fileStream.Position = logFile.Length; // Move to the end of the existing text file
    
                fileStream.BeginWrite(data, 0, data.Length, new AsyncCallback(r =>
                {
                    AsyncState asyncState = r.AsyncState as AsyncState;
    
                    asyncState.FStream.EndWrite(r);
                    asyncState.FStream.Close();
                }), new AsyncState(fileStream, data, m_ManualResetEvent));
    
                m_ManualResetEvent.WaitOne(100, false);
            }
    

    Source download:

    Schedule Management.zip