CVE-2017-20192 in Formidable Forms Plugin
Summary
by MITRE • 10/16/2024
The Formidable Form Builder plugin for WordPress is vulnerable to Stored Cross-Site Scripting via multiple parameters submitted during form entries like 'after_html' in versions before 2.05.03 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts that execute in a victim's browser.
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Analysis
by VulDB Data Team • 12/23/2025
The Formidable Form Builder plugin for WordPress represents a widely used tool for creating custom forms within wordpress environments, yet it contained a critical stored cross-site scripting vulnerability that affected versions prior to 2.05.03. This vulnerability stems from inadequate input sanitization and output escaping mechanisms within the plugin's form processing logic, specifically targeting parameters such as 'after_html' that are processed during form submissions. The flaw allows unauthenticated attackers to inject malicious scripts that persist within the form data storage, making it particularly dangerous as the malicious code executes whenever legitimate users view or interact with the affected forms. This vulnerability directly maps to CWE-79 which defines improper neutralization of input during web output, and aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments, as attackers could potentially embed malicious scripts within form fields to compromise user sessions.
The technical exploitation of this vulnerability occurs when attackers submit malicious payloads through form entry parameters, particularly the 'after_html' field which is designed to accept HTML content for post-form processing. Without proper sanitization, these inputs are stored in the database and later rendered in the user's browser context, creating a persistent XSS attack vector. The vulnerability affects the plugin's form rendering functionality where user-provided content is not adequately escaped before being output to web pages, allowing attackers to execute arbitrary javascript code in the context of a victim's browser session. This stored nature of the vulnerability means that once an attacker successfully injects malicious code, it remains active until the form data is modified or the plugin is updated, potentially affecting multiple users over extended periods.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform session hijacking, steal cookies, redirect users to malicious sites, or even execute more sophisticated attacks such as credential theft or data exfiltration. Attackers could craft malicious forms that, when viewed by administrators or other privileged users, would execute scripts that compromise the entire wordpress installation. The vulnerability particularly affects wordpress environments where administrators or users with form submission privileges might be tricked into submitting malicious content, or where attackers gain access to the form creation interface. The lack of proper input validation and output escaping creates a persistent threat that can be exploited across multiple form entries, making it a significant concern for wordpress administrators managing multiple forms or high-traffic websites.
Mitigation strategies for this vulnerability primarily focus on immediate plugin updates to version 2.05.03 or later, which contain proper input sanitization and output escaping mechanisms. Administrators should also implement additional security measures including input validation at multiple levels, output encoding for all dynamic content, and regular security audits of form fields and user-submitted data. Network-level protections such as web application firewalls can provide additional defense in depth, while monitoring for unusual form submission patterns or content may help detect exploitation attempts. The vulnerability highlights the importance of proper security practices in wordpress plugin development, emphasizing the need for robust input validation and output escaping as fundamental security controls. Organizations should also consider implementing principle of least privilege access controls for form creation and management, limiting the potential impact of such vulnerabilities in compromised environments.