Troubleshooting Tip: Unable to log in to the FortiGate GUI after upgrading to v7.6.4

[lkumar]

Description	This article describes the steps to resolve the issue of being unable to log in to the FortiGate firewall GUI. The issue occurs when the firewall is upgraded to version 7.6.4, and the user is unable to log in to the firewall GUI, despite being able to log in via the CLI.
Scope	FortiGate v7.6.4.
Solution	When the user attempts to log in through the firewall's GUI, an 'Authentication failure' error appears. However, the same credentials work successfully when logging in via the CLI. Note: The issue occurs only while accessing the device via the management interface. Successful authentication can be verified using the following debugs: diagnose debug application httpsd -1 diagnose debug application http_authd -1 diagnose debug enable Workaround: Log in to the FortiGate firewall via the CLI using the same credentials that are used for the GUI. Disable the post-login banner, which is enabled in the global settings using the below command: config system global     set post-login-banner disable end After disabling the banner, the user should be able to log in to the firewall GUI. This issue has been resolved in: v7.6.5. v8.0.0 (scheduled to be released in March 2026). These timelines for firmware release are estimated and may be subject to change. Related article: Technical Tip: Unable to log in to FortiGate GUI after upgrading to v7.6.4 with post-login banner