CVE-2025-66128 identifies a missing authorization vulnerability in the Brevo Sendinblue plugin for WooCommerce, specifically in the newsletter subscription module (woocommerce-sendinblue-newsletter-subscription). This vulnerability arises from incorrectly configured access control security levels, allowing unauthorized users to perform actions that should be restricted. The affected versions include all releases up to and including 4.0.49. The flaw means that an attacker could potentially manipulate subscription data, subscribe or unsubscribe users without permission, or interfere with the newsletter subscription process. Although no public exploits have been reported, the vulnerability's nature suggests that exploitation could be straightforward, as it does not require authentication or complex user interaction. The plugin is widely used in WooCommerce-based e-commerce sites to manage email marketing and customer engagement, making this a significant risk vector. The absence of a CVSS score indicates that the vulnerability is newly disclosed, with limited public technical details. However, the missing authorization issue directly impacts the integrity and confidentiality of user data and could disrupt service availability if abused at scale. The vulnerability was reserved and published in late 2025, with no patches currently linked, emphasizing the need for immediate attention from affected organizations.

For European organizations, especially those operating e-commerce platforms using WooCommerce integrated with Brevo Sendinblue, this vulnerability poses a significant risk. Attackers exploiting this flaw could manipulate newsletter subscriptions, leading to unauthorized data access or modification, which compromises customer privacy and trust. This could result in regulatory non-compliance under GDPR due to unauthorized processing of personal data. Additionally, attackers might disrupt marketing campaigns or inject malicious content via newsletters, harming brand reputation and customer relationships. The potential for service disruption could affect business continuity, especially during peak sales periods. Given the widespread use of WooCommerce in Europe, the impact could be broad, affecting small to large enterprises relying on this plugin for customer engagement and communication.

Organizations should immediately audit their use of the Brevo Sendinblue plugin for WooCommerce and restrict access to the newsletter subscription features to trusted administrators only. Until an official patch is released, consider disabling the plugin or the vulnerable subscription module to prevent exploitation. Implement web application firewall (WAF) rules to detect and block unauthorized access attempts targeting the plugin endpoints. Monitor logs for unusual subscription activity or unauthorized changes. Review and tighten WordPress and WooCommerce user roles and permissions to minimize exposure. Engage with the vendor for timely patch updates and apply them promptly once available. Additionally, conduct regular security assessments of all third-party plugins and maintain an inventory of installed components to quickly identify and remediate vulnerabilities.