Technical Tip: Unable to log in to FortiGate GUI after upgrading to v7.6.4 with post-login banner

After upgrading to version 7.6.4, administrators are unable to log in to the GUI using either local or remote user accounts. After entering valid credentials, the GUI displays an authentication failure message.

This issue is triggered only when the post-login banner is enabled. Logging in through the CLI continues to work normally, even when the post-login banner is enabled.

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

This issue has been resolved in:

• v7.6.5 (available to download from the Fortinet Support portal).
• v8.0.0 (scheduled to be released in March 2026).

These timelines for firmware release are estimated and may be subject to change.

Workaround:

Disable the post-login banner with the CLI commands demonstrated below. Note that this workaround is only applicable if the administrator account is not using Multi-Factor Authentication (MFA).

1. Verify current settings:

get system global | grep post-login

2. Disable the banner:

config system global

    set post-login-banner disable

end

3. Confirm the change:

get system global | grep post-login