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Fortinet Rushes Hotfix as FortiClient EMS Zero-Day Sees Active Exploitation

CISA’s warning elevates the risk level by adding the flaw to its Known Exploited Vulnerabilities list.

Overview

  • Fortinet issued an out-of-band hotfix for FortiClient Enterprise Management Server and told customers on versions 7.4.5 and 7.4.6 to apply it right away, with a permanent fix planned for 7.4.7 and version 7.2 not affected.
  • CISA added CVE-2026-35616 to its Known Exploited Vulnerabilities catalog, which requires U.S. federal agencies to remediate the issue on an accelerated timeline.
  • The bug, rated CVSS 9.1, is an improper access control flaw that lets an unauthenticated attacker bypass the EMS API and run unauthorized code or commands through crafted requests.
  • Security firms Defused and watchTowr reported in-the-wild activity before public disclosure, and Fortinet confirmed ongoing exploitation of the zero-day.
  • This follows a separate FortiClient EMS SQL injection flaw, CVE-2026-21643, that was also exploited, raising stakes because seizing the EMS console can push malicious updates to entire device fleets.