CVE DatabaseCVE-2020-12812

Updated 2026-10-02한국어 권고문 →

CVE-2020-128129.8/CRITICALCISA KEVCWE-178CWE-287CWE-287

Fortinet FortiOS SSL VPN Multi-Factor Authentication (MFA) Bypass Vulnerability (CVE-2020-12812)

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Affected Vendors

fortinet

Affected Components

fortios

Published Date

2020-07-24

CVSS v3.1

9.8

CRITICAL

EPSS (30d)

45.4%

FIRST.org

CISA KEV

Exploited

NVD Source ↗

Executive & SecOps Summary

SECOPS ASSESSMENT

Affected Scope

SSL VPN service running on FortiOS 6.4.0, 6.2.0 to 6.2.3, and 6.0.9 and below

Impact

Attackers can bypass the second-factor authentication (FortiToken) and gain unauthorized access to the internal network by altering the case of the username

Mitigation

Immediately upgrade FortiOS to the patched versions (6.4.1, 6.2.4, 6.0.10 or higher) and audit SSL VPN access logs

Affected Products & Version Scope

FortiOS 6.4.0, FortiOS 6.2.0 to 6.2.3, FortiOS 6.0.9 and below (with SSL VPN enabled)

Remediation & Live Workaround Commands

PATCH & WORKAROUND

1. Official Patch & Version Upgrade Commands

Upgrade the FortiOS firmware to a patched version (6.4.1, 6.2.4, 6.0.10, or higher) as recommended by the vendor. Verify the current version and perform the upgrade via CLI.

bash

# Check current FortiOS system status and version
get system status

# Restore/Upgrade firmware image via TFTP server (replace with appropriate image name and TFTP IP)
execute restore image tftp FGT_60E-v6-build1142-FORTINET.out 192.168.1.99

2. Temporary Workaround & Hardening Configuration

If an immediate upgrade is not feasible, restrict SSL VPN access to trusted source IP addresses to minimize the attack surface.

bash

# Restrict SSL VPN source address in firewall policy
config firewall policy
    edit 10
        set srcaddr 'Trusted_IP_Range'
        set dstaddr 'all'
        set action accept
    next
end

3. Log Audit & IoC Verification Commands

Audit SSL VPN connection logs to identify potential exploitation attempts where usernames with unusual casing successfully established tunnels.

bash

# Filter and display VPN tunnel-up logs to inspect username casing anomalies
show log fortianalyzer filter
execute log filter category vpn
execute log filter field action tunnel-up
execute log display

Interactive SecOps Remediation Checklist

0/4 (0%)

Recommended Security Control & Mitigation Partner

NordLayer / Zero-Trust Network Access

As this vulnerability is actively exploited in the wild (CISA KEV), immediately upgrade all affected FortiOS gateways to the patched releases.

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Technical Root Cause & Exploitation Mechanics

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2020-12812) is an improper authentication issue (CWE-287) combined with case-sensitivity handling errors (CWE-178) within the SSL VPN daemon of Fortinet FortiOS. While the primary authentication mechanism (e.g., LDAP/Active Directory) is case-insensitive and successfully validates the user credentials, the secondary multi-factor authentication (MFA/FortiToken) logic fails to properly handle case mismatches, leading to a logical bypass of the token verification step.

2. Exploitation Mechanics & Attack Scenario

An attacker possessing valid primary credentials (username and password) can exploit this flaw during the SSL VPN login process.

The attacker submits the login request with modified casing in the username (e.g., entering 'John.Doe' instead of the registered 'john.doe').
The FortiOS SSL VPN gateway forwards the credentials to the external authentication server, which successfully authenticates the user regardless of the casing.
The FortiOS MFA engine detects a string mismatch between the configured username and the input username, causing a logical error that skips the FortiToken prompt entirely.
The attacker successfully establishes a VPN tunnel without providing the required second-factor token.

3. Infrastructure & Business Impact

With a CVSS score of 9.8 (Critical) and its inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog, this vulnerability poses an extreme risk. Since SSL VPNs serve as the primary gateway to internal corporate networks, successful exploitation allows external threat actors to bypass MFA controls, establish a persistent foothold, and execute lateral movement, potentially leading to ransomware deployment and sensitive data exfiltration.

Official Vendor Advisories & References

NVD Original English Description

An improper authentication vulnerability in SSL VPN in FortiOS 6.4.0, 6.2.0 to 6.2.3, 6.0.9 and below 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.

https://fortiguard.com/psirt/FG-IR-19-283

Source: psirt@fortinet.com · Vendor Advisory

https://fortiguard.com/psirt/FG-IR-19-283

Source: af854a3a-2127-422b-91ae-364da2661108 · Vendor Advisory

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-12812

Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0 · US Government Resource

Frequently Asked SecOps Questions (CVE-2020-12812)

FAQ

Q1. How critical is CVE-2020-12812 and is it actively exploited in the wild?

CVE-2020-12812 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 45.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.

Q2. Which vendors and products are affected by CVE-2020-12812?

Primary impacted vendors include fortinet across fortios. Scope summary: FortiOS 6.4.0, FortiOS 6.2.0 to 6.2.3, FortiOS 6.0.9 and below (with SSL VPN enabled)

Q3. What temporary mitigations or workarounds exist for CVE-2020-12812 before patching?

[Mitigation] Immediately upgrade FortiOS to the patched versions (6.4.1, 6.2.4, 6.0.10 or higher) and audit SSL VPN access logs Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.

SECOPS WORKBENCH INTEGRATION