Active Directory Logon from Fortinet VPN Subnet (FortiBleed Pivot)

Neharika Razdan@UrzuLaxjoo

•updated Jun 22, 2026•5•0•57

Detects Active Directory logons (Event IDs 4624, 4768, 4769) originating from the Fortinet SSL VPN IP pool. In the context of the FortiBleed credential-harvesting campaign, attackers utilize compromised Fortinet VPN credentials to immediately pivot into internal Active Directory environments. Because pure Sigma rules evaluate a single log source, this rule targets the Windows AD telemetry. To achieve the highest fidelity, this rule should be correlated in your SIEM with FortiGate SSL VPN tunnel-up events (e.g., Event Code 32130, 39424) originating from anomalous external IPs for the same principal within a short time window.