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CVE-2026-18331— Formidable Forms <= 6.33.1 - Unauthenticated Stored Cross-Site Scripting via 'frm_user_id' Parameter

Quick assessment

Affected
strategy11team Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

WordPress 表单构建器插件“Formidable Forms”（用于创建联系表单、计算器、测验等功能）在所有版本（包括 6.33.1 及更早版本）中存在存储型跨站脚本（Stored XSS）漏洞，原因是对其 参数缺乏足够的输入清理和输出转义。这使得未经身份验证的攻击者可以在页面中注入任意 Web 脚本，当用户访问被注入的页面时，这些脚本将会执行。 攻击者通过伪造 使其匹配管理员的用户 ID（该 ID 可通过公共的 WordPress REST API 获取），可以使 成为唯一的输出过滤器。该过滤器会保持注入

CVSS 7.2 · High EPSS 0.37% · P30

Possible ATT&CK Techniques 1 AI

T1059.001 · PowerShell

Affected Version Matrix 1

VendorProduct Version RangeStatus
strategy11team Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More ≤ 6.33.1 affected
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I. Basic Information for CVE-2026-18331

Vulnerability Information
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Vulnerability Title
Formidable Forms <= 6.33.1 - Unauthenticated Stored Cross-Site Scripting via 'frm_user_id' Parameter
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
strategy11team Formidable Forms – WordPress Form Builder for Contact Forms, Calculators, Quizzes & More 0 ~ 6.33.1 -

II. Public POCs for CVE-2026-18331

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III. Intelligence Information for CVE-2026-18331

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News Coverage for CVE-2026-18331 (1)

Other References for CVE-2026-18331 (1)

Other References for CVE-2026-18331 (1)

IV. Related Vulnerabilities

Same vendor: strategy11team
Same weakness: CWE-79

V. Comments for CVE-2026-18331

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