Daily Insight: Control Plane | 2FA Bypass Through Username Case Mismatch

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Assumption Retired 2FA is a reliable perimeter control when properly configured.

Insight Fortinet disclosed active exploitation of FG-IR-19-283 (CVE-2020-12812): a five-year-old FortiOS SSL VPN flaw that bypasses two-factor authentication through username case manipulation. FortiGate treats usernames as case-sensitive; LDAP does not. When local users with 2FA are also members of LDAP groups used in authentication policies, entering a case variant ("Jsmith" instead of "jsmith") prevents local user matching. Under specific configurations, FortiGate then evaluates secondary authentication policies and authenticates against LDAP without enforcing the token. The flaw was patched in July 2020. Fortinet confirmed observed abuse in the wild on December 24, 2025.

Unresolved Edge How many organizations have local users with 2FA referencing LDAP and secondary group policies they forgot existed?