The Timeline Event History plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 3.1 via deserialization of untrusted input 'timelines-data' parameter. This makes it possible for authenticated attackers, with Contributor-level access and above, 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.