CVE-2026-18331

The Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'frm_user_id' 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 frm_user_id to match an administrator's user ID — discoverable via the public WordPress REST API — an unauthenticated attacker causes wp_kses_post() 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.

• CWE-79

• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmEntriesController.php#L752
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmHooksController.php#L69
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L819
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L846
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L982
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L1830
• https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L2083
• https://plugins.trac.wordpress.org/browser/formidable/trunk/js/formidable_admin.js#L1
• https://www.wordfence.com/threat-intel/vulnerabilities/id/f03b09ad-257c-48c9-8ecc-36f60f178f80?source=cve

Published

Aug 26, 2026

Last Modified

Aug 26, 2026

Status

Deferred

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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