CVE-2026-105881 in User Registration Plugin
Summary
by MITRE • 10/13/2026
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in ThemeGrill User Registration user-registration allows Stored XSS.This issue affects User Registration: from n/a through 5.2.8.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security flaw represents a classic instance of Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting or XSS. Specifically, this vulnerability manifests as a Stored XSS within the ThemeGrill User Registration plugin for WordPress, affecting versions ranging from n/a through 5.2.8. Unlike reflected XSS attacks where malicious scripts are executed via manipulated URLs, stored vulnerabilities persist on the target server because the injected payload is saved in databases or other storage mechanisms. In this context, user-supplied input fields within the registration process fail to adequately sanitize or escape special characters before rendering them back into HTML pages for viewing by administrators or other users. This architectural oversight allows an attacker to inject malicious JavaScript code that remains active on the site until manually removed from the database.
From a technical perspective, the root cause lies in insufficient validation and encoding of user input during the registration workflow. When a new user registers through the vulnerable plugin, specific fields such as display names, bio sections, or custom profile data are accepted without rigorous filtering against script injection patterns. The application then stores this untrusted data directly into its backend storage system. Subsequently, when an administrator views the list of registered users or accesses individual user profiles within the WordPress dashboard, the stored malicious payload is retrieved and rendered by the browser as executable code rather than plain text. This failure to neutralize input during web page generation creates a persistent execution environment for arbitrary scripts under the context of the victim's session.
The operational impact of this vulnerability is severe due to its persistence and potential reach. An attacker who successfully exploits this flaw can execute JavaScript in the browser sessions of any user with access to the affected pages, typically WordPress administrators or editors given their role in managing user lists. This capability enables a range of malicious activities including session hijacking, where the attacker steals authentication cookies to impersonate privileged users; credential harvesting by creating fake login forms that capture usernames and passwords; defacement of the website interface; or redirection of victims to phishing sites. Because the payload is stored server-side, it does not require tricking specific individuals into clicking a link, thereby increasing the likelihood of successful exploitation against multiple targets over an extended period.
In terms of industry standard classifications, this vulnerability aligns with CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'). The attack vector corresponds to ATT&CK technique T1059.007: JavaScript, which falls under the broader command and control or collection tactics depending on the payload's intent. Furthermore, since it involves input from users that is stored for later use by others, it also relates to CWE-83: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in a persistent context. The persistence mechanism distinguishes this threat from transient XSS attacks and elevates the risk profile significantly within the OWASP Top Ten framework as A07:2017-Cross-Site Scripting (XSS).
To mitigate this vulnerability, immediate action is required to update the ThemeGrill User Registration plugin to a version later than 5.2.8 where these input sanitization issues have been addressed by the developers. If updating is not immediately feasible, administrators should implement strict server-side validation rules that whitelist allowed characters for all user-input fields and enforce HTML entity encoding on output. Additionally, deploying a Web Application Firewall can provide an additional layer of defense by filtering out known XSS patterns in HTTP requests before they reach the application logic. Regular security audits and code reviews focusing on data flow from input to storage and then to display are essential to prevent similar flaws in future development cycles.