CVE-2025-3582 is a medium-severity vulnerability affecting the Newsletter WordPress plugin versions prior to 8.85. The vulnerability is a Stored Cross-Site Scripting (XSS) issue classified under CWE-79. It arises because the plugin fails to properly sanitize and escape certain form settings, allowing high-privilege users, such as administrators, to inject malicious scripts. Notably, this vulnerability can be exploited even when the 'unfiltered_html' capability is disabled, such as in multisite WordPress setups, which typically restricts HTML input for security reasons. The attack vector requires the attacker to have high privileges (admin level) and some user interaction, as the attacker must input malicious content into the plugin’s form settings. Successful exploitation could lead to persistent XSS attacks, where malicious scripts are stored on the server and executed in the context of other users’ browsers, potentially leading to session hijacking, privilege escalation, or unauthorized actions within the WordPress admin interface. The CVSS 3.1 base score is 4.8 (medium), reflecting the network attack vector, low attack complexity, high privileges required, user interaction needed, and limited confidentiality and integrity impact without availability impact. No known exploits are currently reported in the wild, and no official patches have been linked yet, indicating that the vulnerability is newly disclosed and may require prompt attention from site administrators using the affected plugin.

For European organizations using the Newsletter WordPress plugin, this vulnerability poses a risk primarily to the integrity and confidentiality of their web administration environments. Since exploitation requires admin-level access, the threat is more relevant in scenarios where internal users or compromised admin accounts could inject malicious scripts. The stored XSS could allow attackers to execute arbitrary JavaScript in the context of other administrators or privileged users, potentially leading to session hijacking, theft of credentials, or unauthorized changes to website content or configurations. This could result in data breaches, defacement, or further compromise of the web infrastructure. Given the widespread use of WordPress across European businesses, including SMEs and large enterprises, organizations relying on this plugin for newsletter management could face targeted attacks, especially if they operate multisite WordPress installations where the usual HTML filtering is disabled. The impact is heightened in sectors with strict data protection regulations (e.g., GDPR), where any unauthorized access or data leakage could lead to regulatory penalties and reputational damage.

1. Immediate upgrade to Newsletter plugin version 8.85 or later once available, as this will likely contain the necessary sanitization and escaping fixes. 2. Until a patch is released, restrict plugin access strictly to trusted administrators and review user roles to minimize the number of high-privilege users. 3. Implement Web Application Firewall (WAF) rules to detect and block suspicious script injection patterns in form submissions related to the plugin. 4. Regularly audit and sanitize existing form settings data within the plugin to remove any potentially malicious scripts. 5. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in the WordPress admin interface. 6. Monitor logs for unusual admin activity or unexpected changes in plugin settings that could indicate exploitation attempts. 7. Educate administrators on the risks of stored XSS and safe handling of plugin settings. 8. Consider isolating or sandboxing multisite environments to limit cross-site contamination if feasible.