CVE-2020-12812: 
FortiOS vulnerability analysis and mitigation

An improper authentication vulnerability (CVE-2020-12812) was discovered in FortiOS SSL VPN affecting versions 6.4.0, 6.2.0 to 6.2.3, 6.0.9 and below. The vulnerability allows users to bypass two-factor authentication by simply changing the case of their username during the login process (NVD, FortiGuard).

The vulnerability has been assigned a CVSS v3.1 base score of 9.8 (Critical), with high impact scores across confidentiality, integrity, and availability. The attack vector is network-accessible, requires low complexity, needs no privileges, and can be executed without user interaction. The vulnerability stems from an improper authentication mechanism in the SSL VPN where the system fails to properly validate username case sensitivity during the two-factor authentication process (NVD).

When exploited, this vulnerability allows attackers to bypass the FortiToken second factor of authentication by manipulating the case of their username. This could lead to unauthorized VPN access to internal networks, potentially exposing corporate services that are typically protected behind VPN infrastructure. The impact is particularly severe as it provides attackers with authorized internal network access from an external position (AttackerKB).

Organizations should immediately update their FortiOS installations to versions newer than those affected (6.4.0, 6.2.0 to 6.2.3, 6.0.9 and below). Additionally, implementing proper network segmentation and secondary access controls can help mitigate some of the risks associated with this vulnerability (FortiGuard).