In vBulletin through 5.3.x, there is an unauthenticated deserialization vulnerability that leads to arbitrary file deletion and, under certain circumstances, code execution, because of unsafe usage of PHP's unserialize() in vB_Library_Template's cacheTemplates() function, which is a publicly exposed API. This is exploited with the templateidlist parameter to ajax/api/template/cacheTemplates.

vBulletin through 5.3.x on Windows allows remote PHP code execution because a require_once call is reachable with an unauthenticated request that can include directory traversal sequences to specify an arbitrary pathname, and because ../ traversal is blocked but ..\ traversal is not blocked. For example, an attacker can make an invalid HTTP request containing PHP code, and then make an index.php?routestring= request with enough instances of ".." to reach an Apache HTTP Server log file.

vBulletin 5.x through 5.1.6 allows remote authenticated users to bypass authorization checks and inject private messages into conversations via vectors related to an input validation failure.

The vB_Api_Hook::decodeArguments method in vBulletin 5 Connect 5.1.2 through 5.1.9 allows remote attackers to conduct PHP object injection attacks and execute arbitrary PHP code via a crafted serialized object in the arguments parameter to ajax/api/hook/decodeArguments.

Cross-site scripting (XSS) vulnerability in admincp/apilog.php in vBulletin 4.2.2 and earlier, and 5.0.x through 5.0.5 allows remote authenticated users to inject arbitrary web script or HTML via a crafted XMLRPC API request, as demonstrated using the client name.

The install/upgrade.php scripts in vBulletin 4.1 and 5 allow remote attackers to create administrative accounts via the customerid, htmldata[password], htmldata[confirmpassword], and htmldata[email] parameters, as exploited in the wild in October 2013.

SQL injection vulnerability in index.php/ajax/api/reputation/vote in vBulletin 5.0.0 Beta 11, 5.0.0 Beta 28, and earlier allows remote authenticated users to execute arbitrary SQL commands via the nodeid parameter.