Threat actors are continuing to exploit a critical, now-patched security flaw impacting FortiClient Endpoint Management Server (EMS) deployments to deliver a credential-stealing malware family dubbed EKZ Infostealer.
"The campaign abused trusted endpoint management infrastructure to deliver malware across managed endpoints," Arctic Wolf said. "Threat actors disguised the credential stealer payload as a Fortinet endpoint update, silently executing the malicious executable through PowerShell."
The activity, observed by the cybersecurity company in May 2026, involves the exploitation of CVE-2026-35616 (CVSS score: 9.1), a critical pre-authentication API access bypass leading to privilege escalation. The issue was addressed by Fortinet in FortiClient EMS 7.4.7 and later.
A successful compromise is followed by the threat actor taking steps to modify configurations to defer firmware upgrade reminders, as well as modifying a Remote Access Profile configuration and endpoint policy to insert a malicious script for execution on endpoint devices.
"The observed execution pattern suggests that threat actors used FortiClient's own management pathway to push malicious PowerShell commands to managed endpoints in a way that resembled legitimate management operations," Arctic Wolf said.
"Once the threat actors had a route to modify EMS-managed configuration, every managed endpoint became a potential execution target without requiring a separate intrusion path to each device."
In addition, the attack has been found to leverage "fortitray.exe," a legitimate executable associated with FortiClient to launch a .cmd script file using "cmd.exe." The .cmd script is designed to invoke a Base64-encoded PowerShell script that, in turn, is responsible for downloading a malicious payload, running it, and exfiltrating the results to "83.138.53[.]110" via an HTTP POST request.
The executable, named "FortiEndpoint_Patch.exe," masquerades as an update, but, in reality, is a previously unreported Windows information stealer capable of harvesting sensitive data, such as passwords, cookies, and autofill details such as credit card information, addresses, and phone numbers, from Chromium- and Gecko-based browsers.
The data is written to a log file and saved to the ProgramData directory. It's worth noting that the stealer lacks network-based exfiltration capabilities. It's the PowerShell script that transmits the captured data to the attacker-controlled infrastructure.
"By bypassing API authentication and interacting with EMS functionality in a privileged context, threat actors were able to modify management configuration and push malicious scripts for execution on managed endpoints," Arctic Wolf said.
"Session cookies and saved browser credentials may provide threat actors with follow-on access to cloud services, internal applications, and other authenticated resources, including cases where session reuse may circumvent MFA prompts."
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