CVE-2018-17866 in Ultimate Member - User Profile
Summary
by MITRE
Multiple cross-site scripting (XSS) vulnerabilities in includes/core/um-actions-login.php in the "Ultimate Member - User Profile & Membership" plugin before 2.0.28 for WordPress allow remote attackers to inject arbitrary web script or HTML via the "Primary button Text" or "Second button text" field.
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Analysis
by VulDB Data Team • 04/01/2020
The CVE-2018-17866 vulnerability represents a critical cross-site scripting flaw within the Ultimate Member WordPress plugin ecosystem, specifically targeting the um-actions-login.php file in versions prior to 2.0.28. This vulnerability falls under the CWE-79 category of Cross-Site Scripting, which is one of the most prevalent and dangerous web application security flaws identified by the CWE organization. The vulnerability manifests when the plugin fails to properly sanitize user input in the "Primary button Text" and "Second button text" fields, creating an avenue for malicious actors to inject arbitrary HTML and JavaScript code into the plugin's administrative interface.
The technical exploitation of this vulnerability occurs through the manipulation of input fields that are intended for button text customization within the Ultimate Member plugin's login functionality. Attackers can craft malicious payloads containing script tags or other HTML elements in these fields, which are then executed when administrators or other users view the affected plugin interface. The vulnerability is particularly concerning because it operates at the administrative level where privileged users interact with the plugin, potentially allowing attackers to escalate their privileges or compromise the entire WordPress installation. This type of attack aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, specifically targeting web shell execution through XSS vectors.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data exfiltration, and privilege escalation. When administrators interact with the compromised plugin interface, the injected scripts execute within their browser context, potentially allowing attackers to steal session cookies, modify user permissions, or redirect users to malicious sites. The vulnerability is particularly dangerous in multi-user environments where administrators regularly access plugin settings, as it can affect the integrity of the entire WordPress administration panel. The flaw demonstrates poor input validation and output encoding practices, which are fundamental security principles that should be implemented at every layer of web application development.
Mitigation strategies for CVE-2018-17866 primarily focus on immediate plugin updates to version 2.0.28 or later, which contain the necessary sanitization fixes. Organizations should also implement additional security measures including comprehensive input validation, output encoding, and regular security audits of all WordPress plugins. The vulnerability highlights the importance of proper content security policy implementation and demonstrates why automated security scanning tools should be employed to identify similar issues in third-party WordPress plugins. Security professionals should also consider implementing web application firewalls to detect and block malicious script injection attempts, while maintaining regular patch management procedures to ensure all WordPress components remain up-to-date with the latest security fixes.