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Exploit Released for Critical FortiSIEM Vulnerability (CVE-2025-25256)

August 14, 2025 | 2 MINS READ

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THE THREAT

On August 12th, Fortinet disclosed a critical vulnerability impacting multiple versions of Fortinet FortiSIEM. The flaw, CVE-2025-25256 (CVSS: 9.8), is a remote unauthenticated command injection vulnerability due to improper neutralization of special elements used in an OS command in the affected FortiSIEM versions. Fortinet has confirmed the existence of practical exploit code circulating in the wild, though no active exploitation has been identified at the time of writing. Successful exploitation may result in severe consequences, including full system compromise, remote code execution, theft of sensitive data, and/or malware deployment.

Given the criticality of the vulnerability and the existence of Proof-of-Concept (PoC) exploit code, the eSentire Threat Intelligence team assesses that real-world exploitation is probable in the near term. Organizations operating vulnerable instances of FortiSIEM are recommended to apply the relevant security updates immediately.

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Additional information

Fortinet FortiSIEM is a multi-tenant Security Information and Event Management (SIEM) solution that provides real-time visibility into infrastructure and user activity across on-premise and cloud environments. It is used by enterprises and Managed Service Providers (MSPs) across the United States and worldwide, reflecting its broad adoption.

Following Fortinet’s advisory, the Canadian Centre for Cyber Security (CCCS) issued an alert for CVE-2025-25256, emphasizing the criticality of the vulnerability. CVE-2025-25256's disclosure came shortly after GreyNoise reported a surge in brute-force attacks targeting Fortinet SSL VPNs on August 3rd, 2025. According to GreyNoise, such spikes often precede the disclosure of new vulnerabilities affecting the same vendor. While this does not indicate a direct link between CVE-2025-25256 and GreyNoise’s report, it has prompted some speculation.

CVE-2025-25256 is not specifically classified as a zero-day by Fortinet, and it remains unclear whether it should be considered one. The advisory also did not include Indicators of Compromise (IoCs), as the company stated that exploitation of CVE-2025-25256 does not produce distinctive IoCs. A similar vulnerability, CVE-2023-34992 (CVSS: 9.8), affecting multiple FortiSIEM versions, was identified in October 2023. The PoC exploit code for that flaw revealed an issue with how the phMonitor service in FortiSIEM instance handles incoming requests. A workaround recommended to mitigate CVE-2025-25256 is to restrict access to the phMonitor port (7900), suggesting a similar potential exploit chain.

Given the widespread use of Fortinet FortiSIEM, threat actors are likely to target vulnerable instances using the available PoC exploit code. It is critical for organizations to apply the recommended workaround or security patches promptly to avoid the potential risk of exploitation.

Impacted Versions List:

References:

[1] https://www.fortiguard.com/psirt/FG-IR-25-152
[2] https://nvd.nist.gov/vuln/detail/CVE-2025-25256
[3] https://www.cyber.gc.ca/en/alerts-advisories/fortinet-security-advisory-av25-506
[4] https://www.greynoise.io/blog/vulnerability-fortinet-vpn-bruteforce-spike
[5] https://nvd.nist.gov/vuln/detail/cve-2023-34992
[6] https://horizon3.ai/attack-research/disclosures/cve-2023-34992-fortinet-fortisiem-command-injection-deep-dive/

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