Essential Insights
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Critical Vulnerability Disclosure: Fortinet revealed a severe vulnerability (CVE-2025-64155) in its FortiSIEM platform, scoring 9.4 on the CVSS scale, allowing unauthenticated attackers remote code execution via crafted TCP requests.
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Exploitation in the Wild: Cybersecurity vendor Defused reported active exploitation of this vulnerability shortly after its disclosure, with notable activity traced back to multiple IP addresses, including those from Chinese providers.
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Widespread Attention: The flaw has attracted substantial interest from diverse threat actors, indicating increased exploitation rates compared to similar vulnerabilities, as highlighted by Defused’s analysis.
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Urgent Mitigation Recommended: Fortinet advised customers using vulnerable FortiSIEM versions (6.7 to 7.4) to update immediately, with temporary measures suggesting limiting access to the vulnerable phMonitor service.
Fortinet Faces New Security Challenge
As 2026 unfolds, Fortinet users find themselves grappling with another serious issue. On January 13, the company announced a critical vulnerability in its FortiSIEM platform. This flaw, known as CVE-2025-64155, has earned a high CVSS score of 9.4, indicating severe risk. The vulnerability enables attackers to execute remote code via crafted TCP requests, posing a significant threat to affected systems.
Cybersecurity firm Defused recently reported that this vulnerability has been actively exploited. Their analysis revealed that multiple threat actors, including several from Chinese IP addresses, have targeted FortiSIEM instances. The founder of Defused noted that such malicious activity began almost immediately following the flaw’s disclosure, indicating a swift response from cybercriminals.
A Familiar Attack Surface for FortiSIEM
This vulnerability was first reported to Fortinet by Horizon3, a security research firm. They highlighted that a proof-of-concept exploit likely influenced the recent exploitation attempts. In simpler terms, attackers have used tools and methods publicly shared by researchers to launch assaults on vulnerable systems.
Zach Hanley from Horizon3 explained that the vulnerability arises from issues with FortiSIEM’s phMonitor service. This service, critical for system monitoring, exposes command handlers that any remote user can access without authentication. Although Fortinet has urged users to patch their systems, the recurring nature of these vulnerabilities raises questions about the effectiveness of existing security measures.
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