A critical FortiClient Endpoint Management Server (EMS) vulnerability patched in April has been exploited in fresh attacks to deploy information-stealing malware, Arctic Wolf reports.
The flaw, tracked as CVE-2026-35616 (CVSS score of 9.1), can be exploited remotely via crafted requests for remote code execution (RCE) and does not require authentication.
Fortinet rolled out hotfixes for the security defect in early April, warning that it had been exploited in the wild as a zero-day and urging immediate patching.
Unpatched FortiClient EMS deployments are now being targeted in a campaign deploying the EKZ Infostealer disguised as a fake Fortinet endpoint patch.
The payload was executed via FortiClient-managed VPN scripting workflows, using command scripts that invoked PowerShell, suggesting knowledge of the affected environment.
“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 says.
Because FortiClient EMS functions as a central management platform for FortiClient devices, policies, and configurations, access to the appliance enabled the attackers to execute code on every managed endpoint, the cybersecurity firm notes.
The information-stealing malware deployed in these attacks targets Chrome, Microsoft Edge, Firefox, and other Chromium and Gecko-based browsers for credential, cookie, and autofill data theft. The harvested data is exfiltrated over HTTP.
“The application does not possess network-based credentials exfiltration capabilities; instead, it exports credentials from supported browsers to an output log file. Run without arguments, it provides command-line usage details,” Arctic Wolf notes.
Organizations are advised to apply Fortinet’s patches for CVE-2026-35616 as soon as possible. The security defect was added to CISA’s Known Exploited Vulnerabilities (KEV) list on April 6.
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