Contact Form Plugin by Fluent Forms for Quiz, Survey, and Drag & Drop WP Form Builder <= 5.1.15 - PHP Object Injection via extractDynamicValues

The Contact Form Plugin by Fluent Forms for Quiz, Survey, and Drag & Drop WP Form Builder plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 5.1.15 via deserialization of untrusted input in the extractDynamicValues function. This makes it possible for authenticated attackers, with contributor-level access and above, to inject a PHP Object. 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. Successful exploitation requires the attacker to have "View Form" and "Manage Form" permissions, which must be explicitly set by an administrator. However, this requirement can be bypassed when this vulnerability is chained with CVE-2024-2771.

The attempt arrives as an ordinary request to Fluent Forms: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Fluent Forms 5.1.16 closes this, and updating the plugin is the step that ends it.

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