CVE-2018-13136 in Ultimate Member Plugin
Summary
by MITRE
The Ultimate Member (aka ultimatemember) plugin before 2.0.18 for WordPress has XSS via the wp-admin settings screen.
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Analysis
by VulDB Data Team • 04/03/2023
The vulnerability identified as CVE-2018-13136 affects the Ultimate Member WordPress plugin, a popular user management solution that enables website administrators to create custom registration forms, user profiles, and membership systems. This particular flaw exists in versions prior to 2.0.18 and specifically targets the wp-admin settings screen, making it particularly dangerous as it allows attackers to exploit the vulnerability through the administrative interface where privileged users typically perform critical configuration tasks. The vulnerability falls under the CWE-79 category of Cross-Site Scripting, which represents one of the most prevalent and dangerous web application security flaws in the industry. The attack vector involves malicious script injection that can be executed when administrators visit the plugin's settings page, potentially compromising the entire WordPress installation.
The technical implementation of this vulnerability stems from inadequate input validation and output sanitization within the plugin's administrative settings handling code. When administrators navigate to the Ultimate Member settings screen, the plugin fails to properly sanitize user-supplied input that may be rendered back to the browser without appropriate encoding or filtering mechanisms. This allows an attacker to inject malicious JavaScript code through various input fields within the settings interface, which then executes in the context of the administrator's browser session. The vulnerability is particularly concerning because it leverages the trust relationship between the administrator and the plugin, enabling attackers to execute arbitrary code with the privileges of the logged-in administrator. This represents a classic privilege escalation scenario where a low-privilege attacker can potentially gain full administrative control over the WordPress site.
The operational impact of this vulnerability extends far beyond simple script execution, as it provides attackers with the capability to perform a wide range of malicious activities within the compromised WordPress environment. An attacker who successfully exploits this vulnerability can steal administrative credentials, modify user permissions, inject backdoors into the website, or even completely compromise the entire WordPress installation. The vulnerability also enables the execution of persistent attacks through the injection of malicious scripts that can remain active even after the initial exploitation attempt. This makes it particularly dangerous for websites with multiple administrators or those that rely heavily on user management features. The attack can be amplified by the fact that the vulnerability affects the administrative interface, potentially allowing attackers to modify critical plugin settings or configuration parameters that control user access and authentication mechanisms.
Mitigation strategies for CVE-2018-13136 primarily focus on immediate remediation through the installation of the patched version 2.0.18 or later, which addresses the input validation and output sanitization issues within the plugin's settings handling code. Organizations should also implement network-level protections such as web application firewalls that can detect and block malicious script injection attempts targeting WordPress administrative interfaces. Regular security audits of WordPress plugins and themes should be conducted to identify other potential vulnerabilities that may exist in the broader plugin ecosystem. The vulnerability also highlights the importance of principle of least privilege in WordPress environments, where administrators should limit their exposure by using the minimum required permissions and regularly reviewing access controls. Additionally, implementing proper input validation at multiple layers of the application stack, including both client-side and server-side validation, can help prevent similar XSS vulnerabilities from occurring in other components of the WordPress installation. This vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript and demonstrates the importance of defensive coding practices that prevent the execution of untrusted code in privileged contexts.