CVE-2025-67911 is a security vulnerability classified as deserialization of untrusted data in the Tribulant Software Newsletters plugin, specifically versions up to and including 4.11. This vulnerability allows object injection attacks, which occur when an application deserializes data from untrusted sources without sufficient validation or sanitization. In this context, an attacker can craft malicious serialized objects that, when processed by the plugin, can lead to arbitrary code execution, privilege escalation, or other malicious outcomes such as data manipulation or denial of service. The plugin is commonly used in WordPress environments to manage newsletters and email campaigns, making it a critical component for organizations relying on these communications. The vulnerability was reserved in December 2025 and published in January 2026, but no CVSS score has been assigned yet, and no known exploits have been reported in the wild. The lack of patch links suggests that a fix may not yet be publicly available, increasing the urgency for organizations to monitor vendor communications. The root cause lies in insecure deserialization practices, a well-known attack vector that can bypass traditional input validation and firewall protections. Attackers exploiting this vulnerability do not require authentication, increasing the attack surface. The vulnerability impacts confidentiality by potentially exposing sensitive subscriber data, integrity by allowing unauthorized data manipulation, and availability by enabling denial of service or system crashes.

For European organizations, the impact of CVE-2025-67911 can be significant, particularly for those using the Tribulant Newsletters plugin to manage customer communications. Successful exploitation could lead to unauthorized access to subscriber databases, leakage of personal data protected under GDPR, and potential reputational damage. Furthermore, attackers could execute arbitrary code on the affected servers, leading to full system compromise, lateral movement within networks, or deployment of ransomware. This could disrupt business operations, especially for companies relying heavily on email marketing and customer engagement. The breach of subscriber data could also result in regulatory penalties under European data protection laws. Additionally, the availability of the newsletter service could be impacted, affecting communication channels with customers and partners. Given the plugin’s integration with WordPress, a widely used CMS in Europe, the scope of affected systems could be broad, increasing the potential for widespread impact.

Organizations should immediately inventory their WordPress environments to identify installations of the Tribulant Newsletters plugin, particularly versions 4.11 and earlier. Until an official patch is released, consider disabling the plugin or restricting its use to trusted users only. Implement strict input validation and sanitization on any data that the plugin processes, especially serialized data. Employ web application firewalls (WAFs) with rules designed to detect and block malicious serialized payloads. Monitor logs for unusual deserialization activity or unexpected object injection attempts. Regularly back up affected systems to enable recovery in case of compromise. Stay informed on vendor updates and apply patches promptly once available. Additionally, consider isolating newsletter management systems from critical infrastructure to limit lateral movement if exploited. Conduct security awareness training for administrators managing WordPress plugins to recognize and respond to suspicious activity related to deserialization vulnerabilities.