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CVE-2026-18331

7.2 · HIGH

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…

Published Aug 26, 2026CWE-79EPSS 0.41%

Overview

CVE-2026-18331 is a high-severity vulnerability. It was published on August 26, 2026 and has a CVSS 3.1 base score of 7.2 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.2, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmEntriesController.php#L752Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmHooksController.php#L69Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L819Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L846Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L982Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L1830Refplugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L2083Refplugins.trac.wordpress.org/browser/formidable/trunk/js/formidable_admin.js#L1Refwww.wordfence.com/threat-intel/vulnerabilities/id/f03b09ad-257c-48c9-8ecc-36f60f178f80?source=cve

How CyberStrike helps

Frequently asked questions

What is CVE-2026-18331?

CVE-2026-18331 is a high-severity vulnerability. It was published on August 26, 2026 and has a CVSS 3.1 base score of 7.2 (HIGH).

How severe is CVE-2026-18331?

This vulnerability has a CVSS 3.1 base score of 7.2, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-18331?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-18331?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-18331 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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