CVE-2025-3583 is a stored Cross-Site Scripting (XSS) vulnerability identified in the Newsletter WordPress plugin versions prior to 8.7.1. The vulnerability arises because the plugin fails to properly sanitize and escape certain settings, allowing high-privilege users, such as administrators, to inject malicious scripts. This can occur even when the unfiltered_html capability is disabled, which is a common security restriction in multisite WordPress environments. The vulnerability is classified under CWE-79, indicating improper neutralization of input during web page generation. Exploitation requires high privileges and user interaction, as an attacker must have admin access to inject the payload and a victim user must load the malicious content. The CVSS 3.1 base score is 3.5 (low severity), reflecting limited confidentiality and integrity impact, no availability impact, network attack vector, low attack complexity, and required privileges and user interaction. No known exploits are currently reported in the wild. The vulnerability could allow an attacker to execute arbitrary JavaScript in the context of the affected site, potentially leading to session hijacking, defacement, or further privilege escalation if combined with other vulnerabilities. The lack of a patch link suggests that a fixed version (8.7.1 or later) should be sought from the plugin vendor or WordPress repository to remediate this issue.

For European organizations using the Newsletter WordPress plugin, this vulnerability poses a moderate risk primarily to website integrity and user trust rather than critical infrastructure. Since exploitation requires administrator privileges, the threat is mostly internal or from compromised admin accounts. Successful exploitation could lead to unauthorized script execution, enabling attackers to steal session tokens, manipulate content, or conduct phishing attacks against site users. This could damage brand reputation and lead to regulatory scrutiny under GDPR if personal data is exposed or manipulated. The impact is more pronounced for organizations relying heavily on WordPress for customer engagement, marketing, or internal communications. Multisite WordPress setups, common in larger enterprises or agencies, are specifically vulnerable even with unfiltered_html disabled, increasing the attack surface. However, the low CVSS score and absence of known exploits indicate a limited immediate threat. Still, organizations should prioritize patching to prevent potential chained attacks or insider threats.

Organizations should immediately verify the version of the Newsletter plugin in use and upgrade to version 8.7.1 or later where this vulnerability is fixed. If upgrading is not immediately possible, restrict administrator access strictly to trusted personnel and enforce strong authentication mechanisms such as multi-factor authentication (MFA). Conduct regular audits of admin accounts and plugin settings to detect unauthorized changes. Implement Content Security Policy (CSP) headers to limit the impact of any injected scripts. Additionally, monitor web application logs for unusual activity or script injections. For multisite WordPress environments, review and tighten capability assignments and consider isolating critical sites to minimize risk. Finally, maintain a robust backup and recovery plan to restore sites quickly in case of compromise.