The Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'frmuserid' parameter in all versions up to, and including, 6.33.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. By forging frmuserid to match an administrator's user ID — discoverable via the public WordPress REST API — an unauthenticated attacker causes wpksespost() to serve as the only output filter, which preserves the injected payload structurally intact; the plugin's admin JavaScript then decodes and executes it automatically on page load.

The Formidable Forms WordPress plugin before 6.14.1 does not sanitise and escape some of its settings, which could allow high privilege users such as admin to perform Stored Cross-Site Scripting attacks even when the unfilteredhtml capability is disallowed (for example in multisite setup).

The Formidable Forms WordPress plugin before 6.1 uses several potentially untrusted headers to determine the IP address of the client, leading to IP Address spoofing and bypass of anti-spam protections.

The Formidable Form Builder – Contact Form, Survey & Quiz Forms Plugin for WordPress plugin before 5.0.07 does not sanitise and escape its Form's Labels, allowing high privileged users to perform Cross-Site Scripting attacks even when the unfilteredhtml capability is disallowed

The formidable plugin before 4.02.01 for WordPress has unsafe deserialization.