CVE-2026-18331 json
Formidable Forms <= 6.33.1 - Unauthenticated Stored Cross-Site Scripting via 'frm_user_id' Parameter
published 2mo ago modified 2mo ago also EUVD-2026-66294
- cvss
- 7.2
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.5%
- EPSS 0.5% chance of exploitation in 30 days, percentile 42%
- public exploits
- 0
- none known
Summary
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.
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Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 2mo ago
Exploit prediction
0.49% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 7.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N |
Affected products
- strategy11team Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
- Technology feeds
References
- wordfence.com /threat-intel/vulnerabilities/id/f03b09ad-257c-48c9-8ecc-36f60f178f80?source=cve
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L1830
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L2083
- plugins.trac.wordpress.org /browser/formidable/trunk/js/formidable_admin.js#L1
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/models/FrmEntry.php#L982
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/models/FrmEntry.php#L819
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/models/FrmEntry.php#L846
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/controllers/FrmEntriesController.php#L752
- plugins.trac.wordpress.org /browser/formidable/trunk/classes/controllers/FrmHooksController.php#L69
Sources
- CVE List CVE-2026-18331
- NVD CVE-2026-18331
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.