CVE-2025-9816 is a high-severity stored Cross-Site Scripting (XSS) vulnerability affecting the WordPress plugin 'WP Statistics – Simple, privacy-friendly Google Analytics alternative' developed by veronalabs. This plugin is widely used as a privacy-conscious analytics solution for WordPress sites. The vulnerability exists in all versions up to and including 14.5.4 due to improper neutralization of input during web page generation, specifically insufficient sanitization and output escaping of the User-Agent HTTP header. An unauthenticated attacker can exploit this flaw by injecting malicious JavaScript code into the User-Agent header of HTTP requests. When an administrator or any user with access views the affected statistics pages that render the User-Agent string, the injected script executes in their browser context. This stored XSS can lead to session hijacking, privilege escalation, defacement, or further exploitation within the victim’s browser session. The CVSS v3.1 base score is 7.2, reflecting the network attack vector, no required privileges or user interaction, and a scope change due to the impact extending beyond the vulnerable component. The vulnerability impacts confidentiality and integrity but not availability. No known public exploits have been reported yet, and no official patches were linked at the time of disclosure. The root cause is the failure to sanitize and escape user-controllable HTTP headers before rendering them in the plugin’s admin or statistics interface, a common vector for stored XSS in web applications.

For European organizations using WordPress sites with the WP Statistics plugin, this vulnerability poses a significant risk. Attackers can inject malicious scripts that execute in the browsers of site administrators or users viewing analytics dashboards, potentially leading to credential theft, unauthorized actions, or deployment of further malware. Given the plugin’s focus on privacy-friendly analytics, organizations relying on it for GDPR-compliant data collection may face reputational damage and regulatory scrutiny if exploited. The confidentiality of administrative sessions and data integrity of analytics reports are at risk. While availability is not directly impacted, the indirect consequences of successful exploitation could disrupt operations or lead to site defacement. This is particularly critical for sectors with high-value targets such as finance, healthcare, government, and media organizations in Europe, where WordPress is widely used. The vulnerability’s ease of exploitation without authentication increases the threat level, especially in environments with multiple administrators or editors accessing the plugin’s interface.

Immediate mitigation steps include: 1) Temporarily disabling or restricting access to the WP Statistics plugin’s admin and statistics pages to trusted personnel only. 2) Implementing Web Application Firewall (WAF) rules to detect and block suspicious User-Agent headers containing script tags or encoded payloads. 3) Monitoring web server logs for anomalous User-Agent strings indicative of exploitation attempts. 4) Applying strict Content Security Policy (CSP) headers to limit script execution sources on the WordPress admin interface. 5) Updating the plugin to a patched version once released by veronalabs; if no patch is available, consider replacing the plugin with alternative analytics solutions that properly sanitize inputs. 6) Educating administrators on the risks of XSS and encouraging the use of multi-factor authentication to reduce impact if credentials are compromised. 7) Regularly auditing WordPress plugins for security updates and vulnerabilities to prevent similar issues.