Fortinet Warns July-Disclosed SSL VPN Flaw is Being Used to Bypass 2FA
Published
Key Takeaways
- Active exploitation: Fortinet says attackers are abusing a long-standing SSL VPN flaw.
- Authentication protections: Misconfigurations can allow logins without completing two-factor authentication.
- Legacy systems at risk: Unpatched or poorly configured deployments remain exposed.
Fortinet has issued a new security advisory confirming that threat actors are actively exploiting a vulnerability in FortiOS SSL VPN. Tracked as CVE-2020-12812, it allows bypass two-factor authentication under specific configurations.
The company said the issue affects systems using remote authentication backends where username case handling is inconsistent. The July 2020 vulnerability allows attackers with valid credentials to authenticate without completing the second factor.
Impact, Mitigations, and Broader Context
Although the flaw was originally identified several years ago, it continues to pose a risk in environments that have not applied updates or corrected authentication settings. The vulnerability “may result in a user being able to log in successfully without being prompted for the second factor of authentication (FortiToken) if they changed the case of their username,” PSIRT cautioned.
They urged organizations to review logs for suspicious authentication activity. The vulnerability highlights how configuration weaknesses in deployed perimeter devices can undermine security controls such as multi-factor authentication.
Fortinet recommended disabling affected authentication behaviors, tightening group mappings, updating to supported versions, and resetting credentials where exposure is suspected.
The warning posted on December 24 follows a series of recent Fortinet-related exploitation reports. VPN and edge security devices remain high-value targets for attackers who seek persistent access into enterprise networks.
How the Authentication Bypass Can Occur
FortiGate handles usernames as case-sensitive by default, while LDAP directories typically do not enforce case sensitivity.
The issue arises when users are configured locally on FortiGate with two-factor authentication and are also members of LDAP groups that are referenced in authentication or VPN policies.
If a user logs in using a different capitalization of the same username, FortiGate may fail to match the 2FA user and instead authenticate against LDAP alone, bypassing the second factor.
This could enable unauthorized access to VPN or administrative systems where two-factor authentication is expected.
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