Formidable Forms <= 6.33.1 - Unauthenticated Stored Cross-Site Scripting via 'frm_user_id' Parameter
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-79.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| strategy11team | Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More | up to 6.33.1 | — | No fix listed | CNA |
- Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More Vendorstrategy11team Affected up to 6.33.1 Fixed in — No fix listed CNA
Remediation
No fixed version listed by the sources yet.
Timeline
- 2026-10-02 Threatist record created from CVE-2026-18331
- 2026-10-03 Alias added: GHSA-hjj8-x8wc-9cj2
References
Other 9
- https://www.wordfence.com/threat-intel/vulnerabilities/id/f03b09ad-257c-48c9-8ecc-36f60f178f80?source=cve
- 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://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L982
- 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/controllers/FrmEntriesController.php#L752
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmHooksController.php#L69
More strategy11team vulnerabilities
- TI-2022-03006 AWP Classifieds Plugin < 4.3 - Unauthenticated SQLi CVSS 3.1CRITICAL 9.8
- TI-2023-02696 Formidable Forms < 6.3.1 - Subscriber+ Remote Code Execution CVSS 3.1HIGH 8.8
- TI-2023-01329 Formidable Forms < 6.2 - Unauthenticated PHP Object Injection CVSS 3.1HIGH 7.5
- TI-2023-00774 Formidable Forms < 6.1 - IP Spoofing CVSS 3.1MEDIUM 6.5
- TI-2024-09065 Formidable Forms < 6.14.1 - Admin+ Stored XSS CVSS 3.1MEDIUM 4.8
- TI-2024-04133 SQL injection in strategy11team Business Directory Plugin – Easy Listing Directories for… CVSS 3.1CRITICAL 9.8
Sources
- CVE-2026-18331 · CVE Program
- CVE-2026-18331 · NVD
- FIRST EPSS
- GHSA-hjj8-x8wc-9cj2 · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences