CVE-2018-9034 in Relevanssi Plugin
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in lib/interface.php of the Relevanssi plugin 4.0.4 for WordPress allows remote attackers to inject arbitrary JavaScript or HTML via the tab GET parameter.
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Analysis
by VulDB Data Team • 08/24/2025
The CVE-2018-9034 vulnerability represents a critical cross-site scripting flaw within the Relevanssi plugin version 4.0.4 for WordPress, exposing web applications to persistent security risks. This vulnerability specifically affects the lib/interface.php file where user input from the tab GET parameter is not properly sanitized or validated before being rendered in the web interface. The flaw enables remote attackers to execute malicious JavaScript code within the context of other users' browsers, potentially leading to session hijacking, data theft, or unauthorized actions performed on behalf of victims. The vulnerability resides in the plugin's failure to implement proper input validation and output encoding mechanisms, creating an exploitable entry point for malicious actors seeking to compromise WordPress installations.
This XSS vulnerability operates through the manipulation of the tab GET parameter, which is typically used for navigation or interface state management within the plugin's administrative interface. When the plugin processes this parameter without adequate sanitization, it allows attackers to inject malicious payloads that execute in the browser context of authenticated users. The attack vector is particularly concerning because it can be exploited by unauthenticated users who simply need to craft a malicious URL containing the XSS payload and distribute it to targets. The vulnerability's impact extends beyond simple script execution, as it can facilitate more sophisticated attacks such as credential theft, session manipulation, or redirection to malicious sites. According to CWE-79, this represents a classic cross-site scripting weakness where untrusted data flows from the web application's user interface to the user's browser without proper validation or encoding.
The operational impact of CVE-2018-9034 is significant for WordPress administrators and end-users who rely on the Relevanssi plugin for search functionality. Attackers can exploit this vulnerability to gain unauthorized access to user sessions, potentially escalating privileges or accessing sensitive administrative features. The vulnerability affects any WordPress installation running the vulnerable plugin version, making it particularly dangerous in environments where multiple users have access to the administrative interface. The attack can be executed through simple URL manipulation, making it accessible to attackers with minimal technical expertise. From an ATT&CK framework perspective, this vulnerability maps to techniques involving client-side exploitation and credential access, enabling adversaries to establish persistent access through compromised user sessions. The vulnerability also aligns with the broader category of web application attacks that target user interface components, as outlined in various security frameworks including OWASP's top ten.
Mitigation strategies for CVE-2018-9034 should focus on immediate remediation through plugin updates to version 4.0.5 or later, which contain the necessary patches to address the XSS vulnerability. Administrators should also implement proper input validation and output encoding practices throughout their WordPress installations, ensuring that all user-supplied data is sanitized before processing. Additional protective measures include implementing content security policies to prevent unauthorized script execution, using web application firewalls to detect and block malicious requests, and conducting regular security audits of installed plugins and themes. The vulnerability underscores the importance of maintaining updated WordPress core and plugin versions, as well as implementing defense-in-depth strategies that include monitoring for suspicious user activity and regular security assessments. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates and reduce the window of exposure to known vulnerabilities.