The proc_deutf function in includes/functions_vbseocp_abstract.php in vBSEO 3.5.0, 3.5.1, 3.5.2, 3.6.0, and earlier allows remote attackers to insert and execute arbitrary PHP code via "complex curly syntax" in the char_repl parameter, which is inserted into a regular expression that is processed by the preg_replace function with the eval switch.