Background

On April 4, Fortinet published a security advisory (FG-IR-26-099) for CVE-2026-35616, a critical improper access control vulnerability affecting Fortinet FortiClientEMS.

Analysis

CVE-2026-35616 is a critical improper access control vulnerability affecting Fortinet FortiClientEMS. A remote, unauthenticated attacker can exploit this flaw to execute arbitrary code using specially crafted requests which bypass API authentication.

While no attribution has been provided as of the time this blog was published, the advisory from Fortinet confirms that exploitation has been observed. The advisory credits Simo Kohonen from Defused and Nguyen Duc Anh, who reported the vulnerability to Fortinet. On April 4, Defused released a Linkedin post confirming their observations of zero-day exploitation of this flaw.

At the time this blog was published, Tenable Research has classified this flaw as a Vulnerability of Interest according to our Vulnerability Watch classification system.

Historical Exploitation of Fortinet Devices

Fortinet vulnerabilities have historically been common targets for cyber attackers, with 24 Fortinet CVEs currently on the Cybersecurity and Infrastructure Security Agency’s (CISA) Known Exploited Vulnerabilities (KEV) list, with 13 of those being linked to ransomware campaigns. Targeting of Fortinet flaws have been attributed to a number of threat actors, including Salt Typhoon.

Just over a week ago, Defused reported exploitation in the wild for CVE-2026-21643, SQL injection vulnerability affecting FortiClientEMS. Fortinet’s advisory now reflects that exploitation has been observed but as of April 6, the flaw has not yet been added to the KEV.

🚨 Fortinet Forticlient EMS CVE-2026-21643 - currently marked as not exploited on CISA and other Known Exploited Vulnerabilities (KEV) lists - has seen first exploitation already 4 days ago according to our data

Attackers can smuggle SQL statements through the "Site"-header… pic.twitter.com/pHwl2qMVsj

— Defused (@DefusedCyber) March 28, 2026

At the time this blog was published on April 6, CVE-2026-35616 had not been added to the KEV, however shortly after publication, the KEV was updated to include CVE-2026-35616.

As Fortinet devices have been popular targets for attackers, the Tenable Research Special Operations Team (RSO) has authored several blogs about vulnerabilities affecting these devices. The following table outlines some of the most impactful Fortinet vulnerabilities in recent years.

Proof of concept

As of April 6, a public proof-of-concept has been identified on GitHub, however Tenable Research has not yet verified the exploit. Given the past exploitation of Fortinet devices and published exploit code for several past vulnerabilities, we anticipate that exploitation will continue to increase as additional exploits are released.

Solution

The following table details the affected and fixed versions of Fortinet FortiClientEMS devices for CVE-2026-35616:

As of April 6, Fortinet has provided a hotfix for FortiClient EMS 7.4.5 and 7.4.6 to address this vulnerability. Version 7.4.7 has not yet been released, but will be an upcoming release that addresses this vulnerability. Until that release, the hotfix must be applied to be protected against this vulnerability. We recommend reviewing the security advisory as Fortinet may make future updates to the document.

Identifying affected systems

A list of Tenable plugins for this vulnerability can be found on the individual CVE page for CVE-2026-35616 as they’re released. This link will display all available plugins for this vulnerability, including upcoming plugins in our Plugins Pipeline.

Additionally, customers can utilize Tenable Attack Surface Management to identify public facing assets running Fortinet devices by using the following subscription:

Get more information

• Fortinet FG-IR-26-099 Security Advisory

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