The vulnerability identified as CVE-2024-13521 affects the MailUp Auto Subscription plugin for WordPress, specifically all versions up to and including 1.1.0. This plugin facilitates automatic subscription management for email marketing but contains a critical security flaw due to improper handling of nonce validation in the mas_options function. Nonces are security tokens used to verify that requests come from legitimate users and not forged sources. The absence or incorrect implementation of nonce validation enables Cross-Site Request Forgery (CSRF) attacks, classified under CWE-352. An attacker can craft a malicious request that, when executed by an authenticated site administrator (via clicking a link or visiting a crafted webpage), causes unauthorized changes to the plugin’s settings or injection of malicious scripts. This can lead to unauthorized configuration changes and potential script injection, compromising the confidentiality and integrity of the website and its data. The vulnerability does not affect availability directly. The CVSS 3.1 base score is 6.1, reflecting network attack vector, low attack complexity, no privileges required, but requiring user interaction and impacting confidentiality and integrity with scope change. No patches or exploits are currently publicly available, but the risk remains significant for affected sites, especially those with high-value targets or sensitive user data.

The primary impact of this vulnerability is unauthorized modification of plugin settings and potential injection of malicious scripts, which can lead to data leakage, unauthorized access, or further compromise of the WordPress site. Attackers exploiting this flaw can manipulate subscription settings, potentially redirecting users or harvesting subscriber data. The integrity of site configurations can be undermined, leading to trust issues and reputational damage. While availability is not directly affected, the injected scripts could be used for phishing, malware distribution, or persistent backdoors, escalating the threat. Organizations relying on this plugin for email marketing or user engagement risk exposure of subscriber information and administrative control loss. The attack requires tricking an administrator, so organizations with multiple administrators or less security awareness are at higher risk. The medium severity score indicates a moderate but actionable threat that should be addressed promptly to prevent exploitation.

To mitigate this vulnerability, organizations should immediately update the MailUp Auto Subscription plugin to a version that includes proper nonce validation once available. In the absence of an official patch, administrators can implement manual nonce checks in the mas_options function to validate requests originate from legitimate sources. Restrict administrative access to trusted networks and enforce multi-factor authentication (MFA) to reduce the risk of successful CSRF exploitation. Educate administrators about the risks of clicking unsolicited links and implement Content Security Policy (CSP) headers to limit the impact of injected scripts. Employ Web Application Firewalls (WAFs) with rules to detect and block CSRF attack patterns targeting this plugin. Regularly audit plugin configurations and monitor logs for suspicious changes. Finally, consider disabling or replacing the plugin if a timely patch is not available, especially on high-risk or high-traffic sites.