CVE-2025-64155 is an OS command injection vulnerability in Fortinet's FortiSIEM product, affecting versions 6.7.0 through 7.4.0. The vulnerability arises from improper neutralization of special elements in operating system commands, allowing an attacker to inject and execute arbitrary commands via specially crafted TCP requests. The flaw requires no authentication or user interaction, enabling remote attackers to gain full control over the affected FortiSIEM system. FortiSIEM is a security information and event management (SIEM) solution widely used by enterprises and service providers to monitor and manage security events. Exploitation could allow attackers to execute unauthorized code, leading to data breaches, manipulation or deletion of logs, disruption of security monitoring, and potentially pivoting to other internal systems. The CVSS v3.1 base score is 9.4, reflecting critical severity with high impact on confidentiality, integrity, and availability. Although no public exploits have been reported yet, the vulnerability's characteristics make it a prime target for attackers once exploit code becomes available. Fortinet has not released patches at the time of this report, so organizations must rely on compensating controls. The vulnerability affects multiple FortiSIEM versions, including recent releases, indicating a broad attack surface. Given FortiSIEM's role in security operations, compromise could severely undermine an organization's security posture.

For European organizations, the impact of CVE-2025-64155 is substantial. FortiSIEM is commonly deployed in critical infrastructure sectors, government agencies, financial institutions, and large enterprises across Europe. Successful exploitation could lead to unauthorized access to sensitive security data, manipulation or deletion of logs, and disruption of security monitoring capabilities. This undermines incident detection and response, increasing the risk of prolonged undetected breaches. The ability to execute arbitrary commands remotely without authentication means attackers can fully compromise affected systems, potentially using them as footholds for lateral movement within networks. The loss of integrity and availability of security monitoring data could have cascading effects on compliance with European regulations such as GDPR and NIS Directive, exposing organizations to legal and financial penalties. Additionally, the disruption of security operations centers (SOCs) relying on FortiSIEM could delay response to other concurrent cyber threats. The absence of known exploits currently provides a limited window for mitigation before active exploitation emerges.

Given the absence of official patches at this time, European organizations should implement immediate compensating controls. These include restricting network access to FortiSIEM management interfaces by implementing strict firewall rules and network segmentation to isolate FortiSIEM servers from untrusted networks. Deploy intrusion detection/prevention systems (IDS/IPS) with signatures or anomaly detection tuned to identify suspicious TCP traffic patterns targeting FortiSIEM. Monitor logs and network traffic for unusual activity indicative of command injection attempts. Employ strict access controls and multi-factor authentication for administrative access to FortiSIEM. Disable or limit unnecessary services and interfaces on FortiSIEM appliances to reduce attack surface. Regularly back up FortiSIEM configurations and logs to secure, offline storage to enable recovery in case of compromise. Once Fortinet releases patches, prioritize immediate testing and deployment in all affected environments. Additionally, conduct security awareness training for SOC personnel to recognize signs of exploitation and respond promptly. Engage with Fortinet support and threat intelligence sources for updates and indicators of compromise related to this vulnerability.