CVE-2026-18331
Formidable Forms <= 6.33.1 - Unauthenticated Stored Cross-Site Scripting via 'frm_user_id' Parameter
- 7.2HighCVSS base score
- 0.49%Exploitation in 30 daysEPSS · top 57% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By Wordfence
- 28 days later
· 28 days later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| WordfenceCNA (assigner) | 3.1 | High7.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N |
| NVDNVD · Deferred | 3.1 | High7.2 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.49% · top 57% of all CVEs (10 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.2.
Affected products
References
9
- https://www.wordfence.com/threat-intel/vulnerabilities/id/f03b09ad-257c-48c9-8ecc-36f60f178f80?source=cve (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L1830 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/fields/FrmFieldType.php#L2083 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/js/formidable_admin.js#L1 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L982 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L819 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/models/FrmEntry.php#L846 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmEntriesController.php#L752 (opens in a new tab)
- https://plugins.trac.wordpress.org/browser/formidable/trunk/classes/controllers/FrmHooksController.php#L69 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-66294 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-18331)Record last updated .