CVE-2023-6957 in Fluent Forms Plugin
Summary
by MITRE • 03/13/2024
The Fluent Forms plugin for WordPress by Fluent Forms plugin for WordPress is vulnerable to Stored Cross-Site Scripting in all versions up to, and including, 5.1.9 due to insufficient input sanitization and output escaping. This makes it possible for attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The exploitation level depends on who is granted the right to create forms by an administrator. This level can be as low as contributor, but by default is admin.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 04/17/2025
The vulnerability identified as CVE-2023-6957 affects the Fluent Forms plugin for WordPress, a popular form building solution that enables users to create various types of forms including contact forms, surveys, and payment forms. This security flaw represents a critical Stored Cross-Site Scripting vulnerability that exists in all versions up to and including 5.1.9, making it a significant concern for WordPress site administrators who rely on this plugin for their web applications. The vulnerability stems from inadequate input sanitization mechanisms and insufficient output escaping practices within the plugin's codebase, creating an environment where malicious scripts can be persistently stored and executed without proper validation.
The technical exploitation of this vulnerability occurs when an attacker crafts malicious script code and injects it into form fields or other input areas that are not properly sanitized before being stored in the database. When legitimate users access pages containing these stored malicious scripts, the code executes in their browsers, potentially leading to session hijacking, data theft, or redirection to malicious sites. The attack vector is particularly concerning because the privilege level required to exploit this vulnerability can be quite low, with contributors having the capability to inject malicious code, though the default WordPress user role configuration typically restricts this to administrators. This vulnerability directly maps to CWE-79 which specifically addresses Cross-Site Scripting flaws in web applications, and aligns with ATT&CK technique T1566.001 which covers Spearphishing Attachments in initial access phases.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable sophisticated attack chains where attackers leverage the stored XSS to perform more advanced malicious activities. An attacker who successfully injects malicious code could potentially steal administrator session cookies, modify form data, or redirect users to phishing sites that mimic legitimate services. The persistence of the vulnerability means that once injected, the malicious scripts will continue to execute whenever users access affected pages, making it difficult to contain the damage. This type of vulnerability is particularly dangerous in environments where multiple users have form creation capabilities, as it creates numerous potential entry points for attackers to establish persistent presence within the WordPress environment.
Organizations should immediately implement mitigation strategies including updating to the latest version of the Fluent Forms plugin where the vulnerability has been patched, applying proper input validation and output escaping measures, and considering role-based access controls that limit form creation privileges to trusted administrators only. Security monitoring should include regular scanning for stored XSS vulnerabilities in form inputs and user-generated content areas. The vulnerability also highlights the importance of implementing Content Security Policy headers to prevent execution of unauthorized scripts, and maintaining up-to-date security practices such as regular plugin updates, comprehensive security audits, and user privilege management. Additionally, implementing web application firewalls and intrusion detection systems can provide additional layers of protection against exploitation attempts targeting this class of vulnerability.