Thousands of Fortinet Firewalls Still at Risk Due to Long-Known MFA Weakness (Fortinet SSL-VPN CVE-2020-12812)
- Jan 3
- 2 min read
A significant number of Fortinet firewall devices connected to the internet are still exposed to a known authentication weakness (Fortinet SSL-VPN CVE-2020-12812), years after a fix was made available. Recent security scans show that many organizations continue to run vulnerable configurations, leaving remote access infrastructure open to potential abuse.
The issue affects FortiGate firewalls using FortiOS and relates to how multi-factor authentication is handled on SSL VPN portals. In certain configurations, the system does not properly validate username case sensitivity. This allows an attacker who already has valid credentials to bypass the second authentication factor by simply modifying the capitalization of the username during login.
While the vulnerability was disclosed several years ago and has since been patched by Fortinet, exposed devices continue to appear in large numbers during internet-wide scans. Security researchers tracking these systems report that the problem is not theoretical. Firewalls affected by this weakness are reachable directly from the internet and could be targeted by attackers seeking an initial foothold into corporate networks.
This type of access is especially valuable to threat actors involved in ransomware operations. Once VPN access is obtained, attackers can move laterally, escalate privileges, and deploy additional tools without immediately triggering alarms. The continued exposure of these devices highlights how unpatched perimeter systems remain one of the most common causes of enterprise compromise.
The affected firewalls are spread across multiple regions, with a high concentration in environments where SSL VPN services are publicly accessible. In many cases, organizations are running older FortiOS versions or have not revisited authentication configurations after initial deployment.
Security teams using Fortinet products are advised to review their firewall versions and ensure that all relevant patches have been applied. It is also important to reassess VPN exposure and authentication flows, particularly in environments combining local and external identity providers. Monitoring login activity for unusual patterns can help detect attempted abuse of authentication logic.
This situation serves as another reminder that vulnerabilities do not lose their impact simply because time has passed. Attackers continue to scan for old weaknesses, knowing that patching gaps are common. Keeping network edge devices fully updated remains one of the most effective ways to reduce the risk of intrusion.
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