CVE-2025-3584 is a medium-severity vulnerability classified as CWE-79 (Cross-Site Scripting, XSS) found in the Newsletter WordPress plugin versions prior to 8.8.2. The vulnerability arises because the plugin fails to properly sanitize and escape certain Subscription settings. This flaw allows users with high privileges, such as administrators, to inject and store malicious scripts within the plugin's settings. Notably, this exploitation is possible even when the unfiltered_html capability is disabled, such as in WordPress multisite environments, which typically restricts HTML input to prevent XSS. The attack vector requires high privileges (admin level) and user interaction, as the malicious payload is stored and executed when the affected settings are viewed or processed. The vulnerability impacts confidentiality and integrity by enabling script execution that could hijack admin sessions, manipulate site content, or perform actions on behalf of the admin. Availability impact is not significant. The CVSS score is 4.8 (medium), reflecting the need for high privileges and user interaction, but ease of exploitation is low due to these constraints. No known exploits are currently reported in the wild, and no vendor patches are linked yet, indicating the need for vigilance and prompt patching once available.

For European organizations using WordPress sites with the Newsletter plugin, this vulnerability poses a risk primarily to site administrators and the integrity of their web presence. Successful exploitation could lead to unauthorized administrative actions, defacement, or further compromise of the website, potentially affecting customer trust and data confidentiality. Organizations relying on WordPress multisite setups are particularly at risk since the vulnerability bypasses the usual unfiltered_html restrictions. This could facilitate lateral movement within multisite environments, impacting multiple sites under one administrative umbrella. Given the widespread use of WordPress across Europe for corporate, governmental, and non-profit websites, the vulnerability could be leveraged to target high-value sites, disrupt communications, or conduct phishing campaigns leveraging compromised sites. However, the requirement for admin privileges limits the threat to insiders or attackers who have already gained elevated access, reducing the likelihood of widespread automated exploitation.

European organizations should immediately verify if their WordPress installations use the Newsletter plugin and identify the version in use. Until an official patch is released, administrators should restrict plugin access strictly to trusted personnel and review subscription settings for suspicious content. Implementing Web Application Firewalls (WAFs) with custom rules to detect and block suspicious script payloads in plugin settings can provide interim protection. Organizations should also enforce strong administrative access controls, including multi-factor authentication (MFA) and regular privilege audits, to reduce the risk of privilege escalation or insider threats. Monitoring logs for unusual administrative activity and setting up alerts for changes in plugin settings can help detect exploitation attempts early. Once a vendor patch is available, prompt testing and deployment are critical. Additionally, consider isolating multisite environments and limiting cross-site administrative privileges to minimize potential lateral movement.