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Fake (or Anonymous) NetSend for Windows NT/2000/XP

, 17 Jun 2003
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The Fake NetSend is a little utility that can be used to send anonymous (or fake) messages through your Windows Network.

Introduction

A few years ago I was working at a software development company and one day my co-worker asked me if would be possible to use the Windows Net Send mechanism to send messages through the corporate network using some programming language like C++. I found the idea very interesting since we could implement this functionality in some of our applications so they could send messages to our computers when an exception occurs and/or something goes wrong.

After some time of MSDN and Google, learning about MailSlots, I could write the first test program and, for our surprise, worked like a charm.

With our program ready, we've started do create a generic function to send the messages, so we could make it avaliable at our "shared" directory, when I got an idea: "What if we use an invalid User Name to send the message?". Well, I think I don't need to tell you how this history ends Smile | :)

Background Information

The FakeSend (and Net Send) mechanism is very simple. It uses an Interprocess Communication (IPC) resource called "MailSlots". We can create MailSlots to swap messages between applications on a network environment just like we do with Sockets, Named Pipes, etc... The MailSlot internally uses a datagram socket, which means that we cannot be sure if the message has arrived. To learn more about MailSlots read the MailSlot Reference from MSDN Library.

Using the code

The code is very straightforward. We have the main function NetSend() that receives three values:

  • szSender - The name of the person who is sending the message (Any name you want);
  • szReceiver - The User Name (Network Login) or Machine name of the person who will receive the message;
  • szMessage - The Message you want to send.
bool NetSend(const char * szSender, const char * szReceiver,
             const char * szMessage)
{
    // Our main variables
    char * pszMailSlot = NULL;
    unsigned char * pucMessage = NULL;
    unsigned int nMailSlotLen, nMsgFormatLen;

    HANDLE hHandle;
    DWORD dwBytesWritten;
    bool bRet = false;

    // Get the length of the strings
    nMailSlotLen  = strlen(szReceiver) + sizeof(szMailSlotPath);
    nMsgFormatLen = strlen(szSender) + strlen(szReceiver) +
                    strlen(szMessage) + sizeof(szMsgFormat);

    // Allocate necessary memory
    pszMailSlot = new char[nMailSlotLen];
    pucMessage  = new unsigned char[nMsgFormatLen];

    // Network path for <Receiver> MailSlot:
    // "\\Receiver\MAILSLOT\messngr"
    sprintf(pszMailSlot, szMailSlotPath, szReceiver);

    // Message Format:
    // "Sender\0Receiver\0Message\0"
    // sprintf doesn't work with \0 so here I'm using \r
    sprintf((char *)pucMessage, szMsgFormat, szSender,
                                szReceiver, szMessage);

    // Replace all '\r' characters with '\0'
    for (unsigned short i = 0; i < nMsgFormatLen; i++)
    {
        if (pucMessage[i] == '\r')
            pucMessage[i] = '\0';

        else if (pucMessage[i] == '\0')
            break;
    }

    // Create the file into Receiver's MailSlot and get a Handle to this file
    hHandle = CreateFile(pszMailSlot, GENERIC_WRITE, FILE_SHARE_READ, NULL,
                            OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

    // Do we have a valid handle?
    if (hHandle)
    {
        // Write the message to file
        bRet = (WriteFile(hHandle, pucMessage, (DWORD)nMsgFormatLen,
                    &dwBytesWritten, NULL) == TRUE);

        // Free the handle
        CloseHandle(hHandle);
    }

    return bRet;
}

History

  • 2003-06-08 - First version of FakeSend. Bugs: Zero, I hope Smile | :)
  • 2003-06-11 - Version 1.01. Just improving the code.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Caio Proiete
Software Developer (Senior)
Portugal Portugal
Caio Proiete has been programming for over 10 years, having first started with Clipper Summer'87.
 
He loves software development and reverse engineering. Today his main development technologies includes ASP .NET MVC, jQuery, HTML5, Silverlight, and WCF. He also has the following titles:
 
MVP - Microsoft Most Valuable Professional;
MCT - Microsoft Certified Trainer;
MCPD - Microsoft Certified Professional Developer;
MCTS - Microsoft Certified Technology Specialist;
MCSD - Microsoft Certified Solution Developer;
MCDBA - Microsoft Certified Database Administrator.
 
Technical blog:
http://caioproiete.net
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Comments and Discussions

 
Questiondelphi? Pinmemberp2bf28-Feb-07 7:01 
GeneralNo messages received PinmemberPolovski11-Feb-07 3:27 
GeneralRe: No messages received PinmemberMatheus Lima16-Oct-14 7:49 
QuestionForce line feed in message Pinmemberzhur18-Oct-06 11:48 
Generalfake netSend from c# form PinmemberStojaneee17-May-06 14:41 
Generalsend to all Pinmemberyaewo10-May-06 11:10 
GeneralProblem, program ends very fast PinmemberIustus-aTw31-Mar-06 11:47 
GeneralRe: Problem, program ends very fast PinmemberIustus-aTw3-Apr-06 8:28 
GeneralRe: Problem, program ends very fast PinmemberStojaneee17-May-06 14:33 
QuestionI didn't get a popup box, Why ??? PinmemberKENyroj20-Mar-06 17:47 
GeneralVB6 Code Pinmembermattwright21-Dec-05 10:59 
Could you pleas egive me a link to download the vb6 cource
Generalsudden end of program encounter Pinmembercharllyyy4eva22-Jul-05 3:23 
GeneralSend by IP address PinsussYaroslav A. Golovach9-Jul-05 12:32 
GeneralHi dude! PinmemberGoldSight6-Jun-05 11:19 
GeneralReceive message! PinmemberTailana1-Jun-05 17:04 
GeneralQbasic PinmemberUnknown00425-Jan-05 19:05 
QuestionHow to delete the renamed file PinmemberShadow294-Oct-04 22:59 
AnswerRe: How to delete the renamed file PinsussDrakonas13-Oct-04 20:47 
GeneralANSI or UNICODE Pinmemberponkin28-Sep-04 22:09 
GeneralRe: ANSI or UNICODE PinmemberHernan5-Nov-04 8:01 
Generalmessage length PinmemberHernan23-Jul-04 5:12 
GeneralRe: message length PinmemberCaio Proiete29-Jun-05 12:37 
GeneralMultiple Sends Pinmembermatrixprogrammer20-May-04 17:09 
GeneralRe: Multiple Sends PinmemberCaio Proiete29-Jun-05 12:34 
Generalthank you Pinmemberjalcot27-Apr-04 3:01 

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