CVE-2026-18331

HighCVSS 7.2

Published: 26/08/2026(UTC)Updated: 26/08/2026(UTC)Translated: 26/08/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.37%

30th percentile - higher than 30% of all known CVEs

Summary

The Formidable Forms 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. Unauthenticated attackers can inject arbitrary web scripts that execute when a user accesses an injected page. By forging frm_user_id to match an administrator's user ID, the attacker causes wp_kses_post() to be the only filter, and the script executes automatically.

Risk Assessment

An attacker can execute malicious scripts in the context of an administrator, potentially leading to admin account takeover and full site compromise.

Recommendation

Update Formidable Forms to the latest version and consider restricting access to the REST API if possible.

Other vulnerabilities in Formidable Forms

CVE-2026-11361Medium
The Formidable Forms WordPress plugin before 6.32.1 does not properly validate the status of a PayPal subscription payment before marking it complete. This allows unauthenticated users to bypass payment and trigger paid form actions — such as digital content access, license delivery, and membership activation — without being charged.

Original NVD description (English source)

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.