Client Invoicing by Sprout Invoices <= 20.8.7 - Unauthenticated PHP Object Injection

The Client Invoicing by Sprout Invoices plugin for WordPress is vulnerable to PHP Object Injection in versions up to, and including, 20.8.7 via deserialization of untrusted input. This makes it possible for unauthenticated attackers to inject a PHP Object. No known POP chain is present in the vulnerable software. If a POP chain is present via an additional plugin or theme installed on the target system, it could allow the attacker to delete arbitrary files, retrieve sensitive data, or execute code.