The vulnerability CVE-2020-12812 is an improper authentication flaw in Fortinet FortiOS SSL VPN that allows bypassing two-factor authentication (2FA) due to inconsistent case sensitivity handling between FortiGate local user entries and LDAP directories. FortiGate treats usernames as case-sensitive, while LDAP directories are case-insensitive. When 2FA is enabled on local users referencing LDAP, and these users belong to LDAP groups configured in authentication policies, logging in with a username variant differing only in case causes FortiGate to fail matching the local user entry. Consequently, FortiGate falls back to authenticating directly against LDAP, bypassing 2FA and local user restrictions, including disabled accounts. This flaw requires a specific configuration: local users with 2FA referencing LDAP, membership in LDAP groups, and group-based authentication policies. Fortinet released patches in 2020 (FortiOS 6.0.10, 6.2.4, 6.4.1) and later versions added commands to disable username case sensitivity (e.g., 'set username-case-sensitivity disable'). Active exploitation has been observed recently, though detailed attack vectors and success rates remain undisclosed. The vulnerability enables attackers to authenticate as administrative or VPN users without 2FA, potentially gaining unauthorized access to critical systems. Fortinet recommends disabling username case sensitivity, removing unnecessary LDAP groups, resetting credentials upon suspected compromise, and contacting support for assistance. This vulnerability is particularly concerning for organizations relying on FortiGate SSL VPNs with LDAP-based 2FA configurations.

For European organizations, this vulnerability poses a significant risk to the confidentiality and integrity of sensitive systems accessed via FortiGate SSL VPNs. Unauthorized bypass of 2FA can lead to unauthorized administrative access, data breaches, lateral movement within networks, and disruption of VPN services. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that rely on Fortinet SSL VPNs for secure remote access are especially vulnerable. The ability to bypass 2FA undermines a critical security control, increasing the likelihood of successful credential-based attacks and insider threats. Given the widespread use of Fortinet products in Europe, the vulnerability could facilitate espionage, data theft, or ransomware attacks. The impact on availability is moderate but could escalate if attackers leverage access to deploy malware or disrupt VPN services. The complexity of the exploit is moderate, requiring specific configurations but no advanced user interaction beyond credential submission. The scope includes all FortiGate devices with vulnerable FortiOS versions and affected configurations, potentially impacting thousands of European enterprises and public sector entities.

European organizations should immediately verify if their FortiGate SSL VPN deployments are running vulnerable FortiOS versions and configurations involving local users with 2FA referencing LDAP groups. They must apply Fortinet patches released in 2020 or later versions that address this vulnerability. If patching is not immediately feasible, administrators should disable username case sensitivity using the commands 'set username-case-sensitivity disable' on FortiOS versions prior to 7.0.1 or 'set username-sensitivity disable' on 7.0.1 and later. Removing secondary LDAP groups from authentication policies, if not required, can eliminate the attack vector by preventing fallback LDAP authentication. Organizations should audit authentication logs for unusual login attempts with case-variant usernames and reset credentials for any accounts suspected of compromise. Implementing strict username normalization policies and monitoring for anomalous authentication patterns can help detect exploitation attempts. Additionally, enforcing network segmentation and limiting administrative VPN access reduces potential damage. Coordination with Fortinet support for incident response and guidance is advised. Regular security awareness training emphasizing the importance of 2FA and credential hygiene complements technical controls.