Fortinet’s update servers have deprecated the 5.6 signature format. Fix: Disable the antivirus component of FortiClient in Control Panel > Programs > Modify. Leave VPN functionality enabled.
May 12, 2026 Last Updated: 5 minutes ago Target Audience: IT Administrators, Businesses on Legacy Hardware, VPN Users
Running an EOL VPN client is a significant security gamble. Forticlient 5.6.6 Download
FortiClient 5.6.6 does not support SAML-based SSO or Duo MFA push notifications. It works best with LDAP or local FortiGate users.
For an official, safe , go directly to Fortinet’s support FTP at ftp://ftp.fortinet.com/pub/forticlient/5.6/6/ or log into your Fortinet support portal. Avoid third-party download sites at all costs. Fortinet’s update servers have deprecated the 5
Have questions about migrating away from FortiClient 5.6.6? Fortinet offers a “Legacy VPN Client Migration Guide” for enterprises needing to preserve tunnels while upgrading endpoints. Contact a Fortinet partner for assistance.
Newer FortiClients aggressively push cloud management, ZTNA tags, and telemetry to FortiGate Cloud. Some secure environments (air-gapped, DoD, financial) forbid this. FortiClient 5.6.6 remains a standalone, on-prem VPN client. May 12, 2026 Last Updated: 5 minutes ago
The most secure way is through the Fortinet Customer Service & Support portal. This requires a registered account. to the Support Portal. Navigate to Support > Firmware Download . Select Product : Choose FortiClient from the dropdown.