The issue concerns PHP Object Injection via deserialization of untrusted input. This is made possible through 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. Authenticated attackers with contributor level permissions and above can inject a PHP Object, potentially allowing them to execute code, retrieve sensitive data, or delete files if a POP chain is present.