PHP Object Injection Vulnerability Discovered in a Well Known Plugin – Could Affect 60,000 Websites

The flexible timeline includes the ability to configure viewing preferences and options when viewing the published timeline. Some of these options were passed in PHP’s serialized data format, and unserialized by the define_request_view_params_from_params function in core/timeline/v2/wpbc-class-timeline_v2.php.

An attacker could control the serialized data via several methods:

1. If a timeline was published, an unauthenticated attacker could obtain the nonce required to send an AJAX request with the action set to WPBC_FLEXTIMELINE_NAV and a timeline_obj[options] parameter set to a serialized PHP object.
2. Any authenticated attacker could use the built-in parse-media-shortcode AJAX action to execute the [bookingflextimeline] shortcode, adding an options attribute in the shortcode set to a serialized PHP object. This would work even on sites without a published timeline.
3. An attacker with contributor-level privileges or above could also embed the [bookingflextimeline] shortcode containing a malicious options attribute into a post and execute it by previewing it, or obtain the WPBC_FLEXTIMELINE_NAV nonce by previewing the [bookingflextimeline] shortcode and then using method #1.

Any time an attacker can control data that is unserialized by PHP, they can inject a PHP object with properties of their choice. If a “POP Chain” is also present, it can allow an attacker to execute arbitrary code, delete files, or otherwise destroy or gain control of a vulnerable website. Fortunately, no POP chain was present in the Booking plugin, so an attacker would require some luck as well as additional research in order to exploit this vulnerability. Nonetheless, POP chains appear in a number of popular software libraries, so many sites could still be exploited if another plugin using one of these libraries is installed.