The vulnerability, identified as CVE-2020-12812 and tracked internally as FG-IR-19-283, exploits fundamental differences in how FortiGate processes usernames compared to LDAP directory services.
The authentication bypass occurs when FortiGate’s case-sensitive username handling conflicts with LDAP directories that treat usernames as case-insensitive.
Under specific configurations, this mismatch creates a critical security gap where attackers can circumvent 2FA requirements entirely.
| CVE ID | Vulnerability Type | Affected Product |
|---|---|---|
| CVE-2020-12812 | Authentication Bypass | FortiGate Firewalls |
The vulnerability requires several configuration elements to be present simultaneously. Organizations must have local user entries on FortiGate with 2FA enabled that reference back to LDAP accounts.
These same users need membership in LDAP server groups, such as ‘Domain Users’ or ‘Helpdesk’.
Additionally, at least one LDAP group containing two-factor users must be configured on the FortiGate and used in authentication policies for administrative access, SSL VPN, or IPsec VPN connections.
The exploitation mechanism is straightforward yet effective. When a legitimate user “jsmith” authenticates with proper capitalization, the token request functions correctly.
However, if an attacker uses variations like “Jsmith,” “jSmith,” or “JSMITH,” the FortiGate fails to match against the local user entry.
This mismatch triggers the system to seek alternative authentication options, falling back to LDAP group authentication without enforcing 2FA requirements.
Successful exploitation could grant unauthorized administrative privileges or VPN access without 2FA verification.
Fortinet emphasizes that if exploitation is suspected, organizations should consider their system configurations compromised and reset all credentials, including those used for LDAP/AD binding.
Fortinet addressed the vulnerability in FortiOS versions 6.0.10, 6.2.4, and 6.4.1, released in July 2020.
For organizations unable to upgrade immediately, mitigation involves disabling username case sensitivity on local accounts using the command “set username-case-sensitivity disable” or “set username-sensitivity disable” on newer versions (6.0.13+, 6.2.10+, 6.4.7+, 7.0.1+).
Security experts recommend removing unnecessary secondary LDAP groups to prevent authentication fallback, which eliminates the exploitation pathway entirely when no LDAP groups are configured.
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The post Hackers Abuse 3-Year-Old FortiGate Flaw to Bypass Firewall 2FA Protections appeared first on Cyber Security News.
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