CVE-2026-18146 in Fluent Forms Plugin
Summary
by MITRE • 08/13/2026
The Fluent Forms – Customizable Contact Forms, Survey, Quiz, & Conversational Form Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Notification Smartcode Values in all versions up to, and including, 6.2.11 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute in the browser of an administrator (or any user with the Fluent Forms entry-viewing capability) when they view the form's entry Submission Logs in the WordPress admin dashboard. Exploitation requires that a site administrator or Fluent Forms manager has configured an email notification whose subject or static (direct) Send To value references an attacker-influenced Smartcode such as an input_password field value, a cookie value, or submission.response.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability exists within the Fluent Forms WordPress plugin, specifically affecting versions up to and including 6.2.11, where stored cross-site scripting flaws permit unauthenticated attackers to inject malicious scripts that execute in administrators' browsers when viewing form submissions. This represents a critical security risk as it leverages the plugin's notification system to deliver payloads through smartcode values that are not properly sanitized or escaped before being rendered in the admin dashboard. The flaw stems from inadequate input validation mechanisms that fail to properly process user-supplied data within notification templates, particularly when these templates reference dynamic fields such as password inputs, cookie values, or submission response data.
The technical exploitation occurs through the plugin's handling of smartcode values in email notifications where attackers can manipulate configuration parameters to inject malicious scripts. When administrators view submission logs in the WordPress admin interface, the unescaped smartcode values are rendered directly into HTML output, creating persistent XSS vulnerabilities that affect any user with Fluent Forms entry-viewing privileges including administrators, editors, and managers. This vulnerability operates under the CWE-79 classification for cross-site scripting and aligns with ATT&CK technique T1566.001 for spearphishing attachments, as it enables attackers to establish persistent access through compromised administrator sessions.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the ability to escalate privileges, steal session cookies, perform unauthorized actions within the WordPress admin environment, and potentially gain full control over the affected site. Attackers can leverage this weakness to create persistent backdoors, exfiltrate sensitive data from form submissions, manipulate administrative functions, and maintain long-term access to compromised systems. The vulnerability affects not just individual administrators but also any user with sufficient permissions to view form entries, making it particularly dangerous in multi-user environments where multiple personnel have access to the plugin's administrative features.
Mitigation strategies should focus on immediate patching of the affected plugin versions to address the root cause of insufficient input sanitization and output escaping. Organizations must implement strict input validation processes that sanitize all user-supplied data before processing, particularly within notification templates that reference dynamic fields. The implementation of Content Security Policy headers can provide additional protection against script execution, while regular security audits should verify that all smartcode values are properly escaped in output contexts. Administrative users should be educated about the risks of clicking suspicious links or opening untrusted email notifications that may contain malicious payloads designed to exploit such vulnerabilities. Additionally, organizations should establish monitoring procedures to detect unusual administrative activities that might indicate exploitation attempts, and maintain regular backups to ensure rapid recovery from potential compromise scenarios. The vulnerability demonstrates the critical importance of proper input validation and output escaping in web applications, particularly those handling user-generated content within administrative interfaces where privileged access exists.