CVE-2026-103962 in User Frontend Plugin
Summary
by MITRE • 10/31/2026
The User Frontend – Membership, User Registration, User Profile, User Directory & Content Restriction with Frontend Post Submission plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'field_attr[required]' parameter in all versions up to, and including, 4.3.13 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link. The nonce check on the wpuf_get_child_cat AJAX action is not an effective security barrier because the wpuf_nonce value is publicly localized to every anonymous visitor of any page containing a WPUF shortcode, making it freely harvestable by an unauthenticated attacker.
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Analysis
by VulDB Data Team • 10/31/2026
The WordPress plugin User Frontend – Membership, User Registration, User Profile, User Directory & Content Restriction with Frontend Post Submission contains a critical reflected cross-site scripting vulnerability affecting all versions up to and including 4.3.13. This flaw stems from insufficient input sanitization and output escaping mechanisms within the application code. Specifically, the vulnerability is triggered through the field_attr[required] parameter during AJAX interactions. Because the plugin fails to properly validate or encode user-supplied data before rendering it in the response, an attacker can inject malicious JavaScript payloads that are executed by any victim who views the affected page. This represents a classic instance of reflected cross-site scripting where the malicious script is not stored on the server but rather returned immediately as part of the HTTP response to the initial request.
The operational impact of this vulnerability allows unauthenticated attackers to execute arbitrary web scripts in the context of the vulnerable site's domain. Since no authentication is required to exploit this flaw, any internet user can craft a malicious link containing the injected script and distribute it through phishing emails, social media posts, or other vectors. When an authenticated administrator or regular user clicks on such a link while logged into the WordPress dashboard or frontend interface, their browser will execute the attacker's code. This can lead to session hijacking, where the attacker steals administrative cookies to gain full control over the website. It also enables keylogging, credential theft via fake login forms injected into legitimate pages, and defacement of the user-facing content. The ability to manipulate page content dynamically allows for sophisticated social engineering attacks that appear trustworthy because they originate from a trusted domain.
A significant contributing factor to the severity of this vulnerability is the ineffective implementation of nonce verification in the wpuf_get_child_cat AJAX action. Nonces are typically used to prevent cross-site request forgery by ensuring that requests originated from legitimate forms on the site. However, in this specific plugin version, the wpuf_nonce value is publicly localized and embedded into every page containing a WPUF shortcode. This design flaw means that any anonymous visitor can harvest the nonce simply by viewing the source code of any public-facing page. Consequently, attackers do not need to bypass complex authentication mechanisms or guess secret tokens; they can freely obtain valid nonces from the client side and use them to forge legitimate-looking AJAX requests. This undermines the security model entirely, as the protective barrier intended to validate request origin is rendered useless by its own exposure.
From a classification perspective, this vulnerability aligns with CWE-79 Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting and specifically falls under CWE-614 Sensitive Cookie in Session Without Secure Attribute if session cookies are also compromised due to the script execution. In terms of attack vectors, it maps directly to MITRE ATT&CK technique T1059 Command and Scripting Interpreter via browser-based scripting and potentially T1078 Valid Accounts if used for privilege escalation after stealing credentials. The lack of proper output encoding is a fundamental failure in web application security principles that should be addressed at the code level rather than relying solely on input validation or client-side protections which can be easily bypassed.
Mitigation strategies must focus on immediate remediation and long-term hardening. Administrators running affected versions up to 4.3.13 are strongly advised to update the plugin to the latest patched version where these sanitization issues have been resolved by the developers. If updating is not immediately possible, temporary workarounds include disabling frontend post submission features if they are not essential and restricting access to user registration or profile pages using IP whitelisting or additional authentication layers provided by other security plugins. It is also crucial to implement a Web Application Firewall that can detect and block common XSS payloads in HTTP requests before they reach the application logic. Furthermore, developers should ensure that all dynamic content is properly escaped using functions like esc_html or wp_kses_post depending on the context, and that nonces are generated server-side with strict expiration times rather than being statically embedded in public pages. Regular security audits and code reviews focusing on input handling and output encoding practices will help prevent similar vulnerabilities from arising in future updates.