CVE-2025-25256: 
FortiSIEM vulnerability analysis and mitigation

A critical security vulnerability (CVE-2025-25256) was discovered in Fortinet FortiSIEM, affecting versions 7.3.0-7.3.1, 7.2.0-7.2.5, 7.1.0-7.1.7, 7.0.0-7.0.3, and versions before 6.7.9. The vulnerability is an OS Command Injection flaw that allows an unauthenticated attacker to execute unauthorized code or commands via crafted CLI requests. The vulnerability was disclosed on August 12, 2025, and received a critical CVSS score of 9.8 (Fortinet Advisory, NVD).

The vulnerability exists in the phMonitor service, which listens on TCP port 7900 and is responsible for monitoring the health of FortiSIEM processes. The flaw is specifically located in the function 'phMonitorProcess::handleStorageArchiveRequest' and stems from inadequate sanitization of user inputs through the ShellCmd::addParaSafe function, which only escaped quotes rather than implementing proper command injection protection (WatchTowr Labs).

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary commands on the underlying operating system, potentially leading to complete system takeover. The vulnerability affects FortiSIEM, which is Fortinet's enterprise-grade SIEM solution responsible for real-time event correlation, UEBA-style analytics, and auto-populating CMDB (The Register, WatchTowr Labs).

Fortinet recommends upgrading to the latest fixed versions: 7.3.2 or above for 7.3.x, 7.2.6 or above for 7.2.x, 7.1.8 or above for 7.1.x, 7.0.4 or above for 7.0.x, and 6.7.10 or above for 6.7.x. For users unable to patch immediately, Fortinet suggests limiting access to the phMonitor port (TCP port 7900) as a temporary workaround (Fortinet Advisory).

The disclosure coincided with reports from GreyNoise about a significant spike in brute-force traffic targeting Fortinet SSL VPNs, with more than 780 unique IPs attempting unauthorized access. While a direct causal link between the brute-force activity and the CVE disclosure cannot be confirmed, security researchers noted that such spikes often precede the disclosure of new vulnerabilities affecting the same vendor (The Register).