Detect CVE-2026-35616 — Fortinet FortiClient EMS Improper Access Control Exploitation in Sumo Logic CSE
Detects exploitation attempts targeting CVE-2026-35616, an improper access control vulnerability (CWE-284) in Fortinet FortiClient Enterprise Management Server (EMS). This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild. Attackers may leverage this flaw to bypass access controls on the EMS server, potentially enabling unauthorized configuration changes, endpoint agent manipulation, or lateral movement through managed endpoints.
MITRE ATT&CK
Sumo Detection Query
_sourceCategory=fortinet* OR _sourceCategory=*ems* OR _sourceCategory=*forticlient*
| parse regex "(?i)(?P<event_type>access denied|authorization fail|privilege escal|unauthorized|bypass|improper access)" nodrop
| parse regex "src=(?P<src_ip>[\d\.]+)" nodrop
| parse regex "dst=(?P<dst_ip>[\d\.]+)" nodrop
| parse regex "user=(?P<username>\S+)" nodrop
| where !isNull(event_type)
| timeslice 5m
| stats count AS event_count, values(src_ip) AS source_ips, values(event_type) AS event_types BY _timeslice, username, _sourceHost
| where event_count > 2
| sort by event_count descSumo Logic query aggregating FortiClient EMS access control failure events by 5-minute time slices, grouping by username and source host. Filters noise by requiring more than 2 events per window, surfacing persistent exploitation attempts against CVE-2026-35616.
Data Sources
Required Tables
False Positives & Tuning
- EMS server restarts causing burst of access failure events from all managed endpoints simultaneously
- Certificate rotation on EMS causing temporary authentication failures across the fleet
- Bulk FortiClient policy updates triggering access re-evaluation events at scale
- IT helpdesk remote management sessions to EMS from non-standard source IPs
Other platforms for CVE-2026-35616
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1FortiClient EMS Unauthenticated API Endpoint Probe
Expected signal: Web server access log entries on EMS showing HTTP requests to API paths from an unknown source IP, with response codes logged. Network flow records show connections from test host to EMS port 8013.
- Test 2FortiClient EMS Privilege Escalation via Access Control Bypass (Simulated)
Expected signal: EMS audit log entries recording the low-privilege user's access attempts to admin-tier endpoints. Windows Security Event Log 4648 if token acquisition involved explicit credential use.
- Test 3FortiClient EMS Management Port Reconnaissance from External Network Segment
Expected signal: Network IDS/IPS alerts for port scan activity targeting EMS management ports. Firewall deny logs if EMS ports are restricted. NetFlow records showing probe connections from test segment to EMS IP.
- Test 4FortiClient Agent Mass Policy Modification via Compromised EMS
Expected signal: EMS audit log entry recording policy creation event with the admin token's associated username. API access log entry for POST to /api/v1/policies. Managed endpoint logs showing receipt of new policy push if EMS propagates it.
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