strategy11team Formidable Forms Plugin up to 6.33.1 on WordPress wp_kses_post frm_user_id cross site scripting

Summaryinfo

A vulnerability identified as problematic has been detected in strategy11team Formidable Forms Plugin up to 6.33.1. This affects the function wp_kses_post. The manipulation of the argument frm_user_id leads to cross site scripting. This vulnerability is referenced as CVE-2026-18331. Remote exploitation of the attack is possible. No exploit is available.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in strategy11team Formidable Forms Plugin up to 6.33.1. This issue affects the function wp_kses_post. The manipulation of the argument frm_user_id with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

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.

The advisory is shared at wordfence.com. The identification of this vulnerability is CVE-2026-18331 since 07/29/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059.007 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• WordPress Plugin

Vendor

• strategy11team

Name

• Formidable Forms Plugin

Version

• 6.33.0
• 6.33.1

CPE 2.3info

• 🔒
• 🔒

CPE 2.2info

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• 🔒

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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