The Betheme theme for WordPress is vulnerable to PHP Object Injection in versions up to, and including, 26.5.1.4 via deserialization of untrusted input supplied via the import, mfn-items-import-page, and mfn-items-import parameters passed through the mfn_builder_import, mfn_builder_import_page, importdata, importsinglepage, and importfromclipboard functions. This makes it possible for authenticated attackers, with subscriber level permissions and above to inject a PHP Object. The additional presence of a POP chain would make it possible for attackers to execute code, retrieve sensitive data, delete files, etc..
CWE-502, CWE-502