How to change a user's password on a remote computer

Password Changer screenshot

Introduction

This is my first article on CodeProject. So please don't expect too much. ;-)

Given scenario

An old workstation running Windows 2000 acts as a "file server". Users can access shared folders over the network by connecting using a username and password. Unfortunately, in a workgroup environment, there is no built-in way to change the passwords of these local users from a remote machine.

Tasks to solve

The described problem can be divided into three main parts:

How to get a list of all the computers in our workgroup?
How to get a list of all users from a specific computer?
How to change a user's password on a remote computer?

The API is your friend

In the MSDN are three corresponding network management functions mentioned. Their usage is well explained, so I won't recite the MSDN.

But the simple NetUserChangePassword function prototype should be self-explanatory.

DWORD NetUserChangePassword(
  LPCWSTR domainname,
  LPCWSTR username,
  LPCWSTR oldpassword,
  LPCWSTR newpassword
);

Naming conventions

The different strings (e.g., usernames, passwords) are limited to a certain number of characters. It seems that these limitations are a relic from the NT LAN Manager.

Name	Length
Domain/Workgroup	15
Server	15
User	20
Password	14

Security concerns

NetQueryDisplayInformation requires anonymous access to the remote machine. Furthermore, an established NULL session connection (e.g., to $IPC) is required.

Using the code

The server and the user enumeration are wrapped into several classes.

Enumeration classes

Iterating through the result list shouldn't be a big deal.

NetObjectEnumerator *noe = 
   new [ NetServerEnumerator(Domain) | NetUserEnumerator(Server) ] ;
if(noe->GetError() == ERROR_SUCCESS){
  while(noe->HasNext()){
    NetObject *no = noe->GetNext();
    ... = no->name; // process the current server/user name...

  }
}
else
  ... = NetObjectEnumerator::GetErrorMessage(noe->GetError());
  // process the occurred error...

Error codes and message strings

The FormatMessage function maps an error code to a message. For network management errors, the netmsg.dll module is used to look up the specified errors.

CString GetErrorMessage(DWORD dwLastError){
  HMODULE hModule = NULL;
  DWORD dwFormatFlags = FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_IGNORE_INSERTS | FORMAT_MESSAGE_FROM_SYSTEM;
  LPTSTR lpMessageBuffer = NULL;
  if((dwLastError >= NERR_BASE) && (dwLastError <= MAX_NERR)){
    hModule = LoadLibraryEx(_T("netmsg.dll"), NULL, LOAD_LIBRARY_AS_DATAFILE);
    if(hModule != NULL)
      dwFormatFlags |= FORMAT_MESSAGE_FROM_HMODULE;
  }
  FormatMessage(
    dwFormatFlags,
    hModule,
    dwLastError,
    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
    (LPTSTR)&lpMessageBuffer,
    0,
    NULL);
  CString szMessage;
  szMessage.Format(_T("%s (%u)"), lpMessageBuffer, dwLastError);
  LocalFree(lpMessageBuffer);
  if(hModule != NULL)
    FreeLibrary(hModule);
  return szMessage;
}

Credits

Credits go to Chris Maunder for his great HyperLink static control.

Notice

The application has not been tested in a domain environment. Any volunteers?

Please feel free to send your feedback to me via email. Bug reports, spelling corrections, opinions, and comments would be much appreciated.

History

05/16/2006:

Original article published.
Version 1.0.0.1 released

The newest Password Changer version is also available on my website.

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Access Denied?
MattOliver

16:04 24 Oct '09

Hello, When ever I try to change the password using this tool on a remote computer I get access denied. Any suggestions?
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Nice one...and for Visual Studio 2003?
rootdial

0:48 6 Jan '07

Hi, this is a nice example. Well done But it seems impossible to open under Visual Studio 2003. Is it only designed for 2005?
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Re: Nice one...and for Visual Studio 2003?
Steffen Lange

7:47 6 Jan '07

Hi!

Thanks. It's nice to hear that my tool is useful for others.

The tool was created using Visual Studio 2005. But it should also compile under Visual Studio .Net and 2003 (with MFC7), because there is no specific MFC8 stuff used.

You can try to convert the project file using this little tool: http://www.sliver.com/dotnet/whidbeyprojectconverter/[^].

In the next update I'll try to add a VS .Net or 2003 project... So please be patient! Smile

Steffen

Steps to compile the English version
Steffen Lange

10:20 29 May '06

1. Unzip PwdChange_src.zip 2. Delete PwdChange.rc (German resource script) 3. Rename PwdChange_en.rc to PwdChange.rc 4. Open PwdChange.sln in Visual Studio 2005 That's all folks!
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Re: Steps to compile the English version
Herbert Yu

11:54 26 Oct '06

Great. Actually, you can do better and make single exe contain both languages. --- Herbert Yu Are you sure the speed of computer industry is proper? Are you sure the software you released is a bug free one?
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