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Introduction:
The Gentlemen ransomware-as-a-service (RaaS) operation, which surfaced in mid-2025, has already claimed over 332 victims in the first five months of 2026 by systematically exploiting exposed Fortinet FortiGate VPN appliances and Cisco edge devices. Rather than deploying sophisticated endpoint malware, this group weaponizes the very trust that organizations place in perimeter infrastructure—turning VPN gateways, firewalls, and remote access systems into initial compromise vectors. Understanding how to harden these edge devices and redesign network trust models is now critical for any security team facing modern ransomware.
Learning Objectives:
- Identify common misconfigurations and patch gaps in Fortinet and Cisco edge devices that RaaS affiliates exploit.
- Implement specific hardening commands and policies for FortiGate, Cisco ASA, and Firepower appliances.
- Apply zero-trust segmentation and privilege isolation to contain lateral movement after perimeter compromise.
You Should Know:
- Why Edge Devices Are the New RaaS Goldmine – The Trust Gateway Problem
The Gentlemen group’s success stems from a fundamental architectural flaw: centralized perimeter trust. When a VPN appliance or firewall is compromised, all network trust collapses because the device is implicitly trusted to pass traffic, authenticate users, and enforce policy. Attackers don’t need to break every system—just the one at the edge.
Step‑by‑step attacker methodology observed in the wild:
- Scan for exposed Fortinet SSL-VPN (port 443) or Cisco AnyConnect (port 8443) interfaces.
- Exploit unpatched vulnerabilities (e.g., CVE-2024-21762, CVE-2023-27997 for Fortinet; CVE-2023-20269 for Cisco ASA).
- Use valid credentials obtained via brute-force or phishing to log in legitimately.
- Disable logging or create a second admin account.
- Tunnel internal scanning traffic through the compromised edge device to map the network.
- Deploy ransomware laterally using PsExec, WMI, or scheduled tasks.
To detect if your edge device may already be targeted, run these checks:
Linux (from internal jump host scanning your edge public IP):
Check for open VPN ports on your public range nmap -p 443,8443,4443 --script ssl-enum-ciphers <your_public_fortinet_IP> Test for known SSL-VPN path exposure curl -k https://<your_fortinet_IP>/remote/login?lang=en -I
Windows (PowerShell test for Cisco ASA responsive services):
Test-NetConnection -ComputerName <cisco_public_IP> -Port 8443 (Invoke-WebRequest -Uri "https://<cisco_IP>/+CSCOE+/logon.html" -SkipCertificateCheck).StatusCode
- Hardening Fortinet FortiGate Appliances – Commands and Configurations
FortiGate devices are prime targets because SSL‑VPN and management interfaces are often left exposed. The Gentlemen group’s affiliates scan for FortiOS versions older than 7.0.12 or 7.2.5, which contain known pre‑auth RCE flaws.
Step‑by‑step FortiGate lockdown:
1. Restrict administrative access to trusted IPs only:
config system admin set trusthost1 <internal_mgmt_subnet> 255.255.255.0 set trusthost2 <SOC_IP> 255.255.255.255 end
- Disable SSL‑VPN if not absolutely required. If needed, enforce MFA and limit cipher suites:
config vpn ssl settings set servercert "Your_Cert" set force-two-factor-auth enable set ssl-max-proto-ver tls1-2 set banned-cipher "AES256-SHA:AES128-SHA" end
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Enable logging to a remote SIEM so an attacker cannot locally erase traces:
config log setting set remote-logging enable set remote-format syslog end config log syslogd setting set status enable set server "10.10.10.50" (your SIEM IP) end
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Check for unauthorized admin accounts (common after compromise):
show system admin | grep -A 5 "edit" diagnose system admin list
5. Verify current firmware and known vulnerabilities:
get system status | grep "Version" Compare against Fortinet PSIRT advisories
- Cisco Edge Device Hardening – ASA, Firepower, and IOS Commands
Cisco edge devices (ASA with AnyConnect, Firepower Threat Defense) are similarly abused. The Gentlemen group looks for devices with outdated software, default local authentication, or weak VPN group policies.
Step‑by‑step Cisco ASA/Firepower hardening:
- Enforce certificate‑based or MFA for VPN – disallow password-only authentication:
tunnel-group <group_name> general-attributes authentication-server-group (your_radius_server) LOCAL secondary-predefined-auth-method LOCAL
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Limit VPN session timeouts and concurrent logins to hinder lateral movement:
group-policy <policy_name> attributes vpn-session-timeout 28800 (8 hours) vpn-idle-timeout 30 vpn-simultaneous-logins 1
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Restrict management access to dedicated interfaces and enable logging:
logging host inside 10.10.10.50 logging trap informational no logging monitor access-list mgmt_access extended permit tcp host <SOC_IP> any eq ssh access-group mgmt_access in interface management
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Check for backdoor accounts or privilege escalation after suspected compromise:
show running-config | include username show aaa local user show vpn-sessiondb detail anyconnect
5. Review running config for exposed webvpn endpoints:
show running-config webvpn Remove any unnecessary "url-list" or "port-forward" entries
- Network Segmentation – Stopping Lateral Movement from the Edge
Once a Fortinet or Cisco edge device is compromised, attackers move laterally using internal trust. The Gentlemen group uses standard tools like nmap, crackmapexec, and impacket. Stop them with micro-segmentation and host-based firewalls.
Linux – Implement strict iptables rules on internal servers:
Allow only specific jump hosts to SSH and SMB iptables -A INPUT -p tcp --dport 22 -s 192.168.10.0/24 -j ACCEPT iptables -A INPUT -p tcp --dport 445 -s 192.168.20.0/24 -j ACCEPT iptables -A INPUT -j DROP Persist (Ubuntu/Debian) apt-get install iptables-persistent; netfilter-persistent save
Windows – Use PowerShell to restrict inbound RDP and SMB to authorized subnets:
Block RDP (port 3389) except from management subnet New-NetFirewallRule -DisplayName "Block RDP except mgmt" -Direction Inbound -Protocol TCP -LocalPort 3389 -Action Block -RemoteAddress "10.0.0.0/8" New-NetFirewallRule -DisplayName "Allow RDP from mgmt" -Direction Inbound -Protocol TCP -LocalPort 3389 -Action Allow -RemoteAddress "192.168.100.0/24"
VLAN isolation (step‑by‑step on Cisco switch):
vlan 100 name USER-NET vlan 200 name SERVER-NET interface vlan 100 ip access-group BLOCK_TO_SERVER in ip access-list extended BLOCK_TO_SERVER deny tcp any any eq 445 deny tcp any any eq 3389 permit ip any any
- Visibility and Continuous Monitoring – Detecting Edge Compromise Early
Most organizations discover the Gentlemen only after ransomware deploys. Proactive monitoring of edge device logs and netflow can cut dwell time.
FortiGate – Enable real‑time SSL‑VPN anomaly detection:
config log memory setting set status enable set severity warning end Check for multiple failed login spikes diagnose vpn ssl statistics | grep "login failed"
Cisco ASA – Monitor for unusual VPN session origination:
show logging | include "User %s locked out" | include "VPN" Watch for simultaneous sessions from same source but different users
Linux – Collect netflow data using nfdump:
sudo apt-get install nfdump Capture traffic to/from edge device IP nfcapd -w -D -l /var/flows/ -p 9995 -e nfdump -r /var/flows/nfcapd.202605180000 -s ip -S 192.168.1.1 (edge IP)
Windows – Monitor sysmon events for SMB enumeration:
Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-Sysmon/Operational'; ID=3} | Where-Object {$<em>.Message -like "445" -and $</em>.Message -like "192.168."}
- Incident Response – Detecting Compromise on Edge Devices
If you suspect The Gentlemen have already hit your Fortinet or Cisco edge, immediate triage is required.
FortiGate response commands:
List all admin sessions (including hidden ones) diagnose system admin list Show all active SSL-VPN tunnels with internal IP mappings diagnose vpn ssl list Check for unexpected outbound connections from the FortiGate itself diagnose sys connection list | grep -E "ESTABLISHED|SYN_SENT" Review system events for config changes execute log display | grep -i "config change"
Cisco ASA response:
show users (lists all current CLI sessions) show vpn-sessiondb summary show processes cpu | include ssh|vpn show logging | include "%ASA-4-406001" (FTP bounce attack)
Check for persistence mechanisms – look for scheduled tasks or cron jobs on edge devices that call out to C2:
On FortiGate (advanced diagnostic) dia sys cfs show schedule On Cisco more system:running-config | include event
- Zero‑Trust Architecture – Reducing Trust Exposure Beyond the Perimeter
As Marius Barczak noted, this is an architectural exposure problem. Relying on stronger detection is insufficient. Implement survivable design principles:
- Operational segmentation – No device should trust another solely because they are on the same “inside” network.
- Privilege isolation – Use JIT (just-in-time) admin access via PAM systems for edge devices.
- Minimized trust exposure – Host any VPN termination on separate jump boxes, not on the core firewall.
- Hardened access boundaries – Require client certificates with hardware binding for VPN authentication.
Step‑by‑step micro-segmentation using open-source tools:
- Install OpenZiti (zero-trust overlay) on internal servers – no open inbound ports needed:
Ubuntu – enroll server into overlay network curl -sSL https://get.openziti.io/quickstart/install.sh | bash ziti-edge-tunnel enroll --jwt <server_jwt>
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Create a deny-by-default firewall policy on Windows using PowerShell:
Set-NetFirewallProfile -All -DefaultInboundAction Block Set-NetFirewallProfile -All -DefaultOutboundAction Allow Then explicitly allow only required flows New-NetFirewallRule -DisplayName "DNS" -Direction Inbound -Protocol UDP -LocalPort 53 -Action Allow
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Force all administrative access to edge devices through a bastion host – no direct SSH/HTTPS from user VLANs.
What Undercode Say:
- Attackers are no longer targeting endpoints; they target “trust gateways” – VPNs, firewalls, and edge appliances – because compromising one trusted component collapses network trust and accelerates lateral movement.
- Operational inconsistency (slow patching, weak auth, stale configs, poor segmentation) is easier to exploit than well-managed environments. RaaS groups scale because enterprises fail at consistent hygiene, not because of advanced zero‑days.
- Future ransomware operators will increasingly use AI to automate edge device fingerprinting and tailor exploits to specific firmware versions, reducing time‑to‑ransom from weeks to hours. The only sustainable defense is to redesign infrastructure around minimized trust exposure and survivable architecture principles, not stronger detection alone.
Prediction:
Within the next 12–18 months, RaaS operations like The Gentlemen will shift from opportunistic scanning to AI‑driven, adaptive edge exploitation – automatically identifying Fortinet and Cisco appliances with patch latency, brute‑forcing credentials via leaked password databases, and even generating custom exploit chains on the fly. Organizations that continue to treat edge devices as trusted perimeters will see breach dwell times drop below 24 hours. However, those adopting zero‑trust overlays, micro‑segmentation, and Just‑In‑Time privilege access will force attackers to find new attack surfaces. The cybersecurity industry will see a wave of “edge disconnection” frameworks where VPNs are replaced by application‑layer tunnels with per‑packet authentication. The arms race will move from patching CVEs to eliminating implicit trust entirely – otherwise, the Gentlemen’s 332 victims will be just a rounding error.
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