Fortios
CVE-2020-12812
CRITICAL
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2021 - Vulnerable and Outdated Components
ASVS 5.0
V14 - Configuration Dependency management, component inventory
|
| Impact | Critical risk (CVSS 9.8). This vulnerability completely undermines MFA enforcement on Fortinet VPN infrastructure. Any attacker with stolen passwords can bypass 2FA, making credential theft attacks fully effective. |
| Exploit ScenarioDerived | An attacker obtains VPN credentials through phishing or credential stuffing. The target has MFA enabled with FortiToken. The attacker simply changes the case of the username (e.g., 'USER@corp.com' instead of 'user@corp.com'), bypasses 2FA entirely, and gains VPN access to the corporate network. |
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Alert meAnalysisAIv1 – Mar 26, 2026
FortiOS SSL-VPN contains an improper authentication vulnerability that allows users to bypass two-factor authentication by changing the case of their username, undermining MFA security controls.
Earlier versions of this analysis (1)
An authentication flaw in FortiOS SSL-VPN allows users to bypass FortiToken two-factor authentication by submitting their username with altered case (e.g., uppercase instead of lowercase).
RemediationAI
Upgrade FortiOS immediately. Review VPN authentication logs for case-variant login attempts. Ensure all remote access requires properly enforced MFA that cannot be bypassed through case manipulation.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
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Technical ContextAI · show details
The CWE-178 case-sensitivity flaw means the 2FA lookup treats 'admin' and 'Admin' as different users. The password validation is case-insensitive (matching the AD backend), but the FortiToken association lookup is case-sensitive. Logging in with a different-case username passes password auth but skips the 2FA check.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
Lifecycle Timeline
2DescriptionNVD
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.
Executive ViewAI
CVE-2020-12812 presents critical security risk rated CVSS 9.8. Successful exploitation could critically impact the confidentiality, integrity, and availability of affected systems. This vulnerability is actively exploited in the wild (KEV-listed) and requires immediate remediation. Immediate patching is required per CISA KEV mandate.
Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.
Threat Intelligence Overview
NVD
CVE.org
CISA KEV
EPSS
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Affected Products (CPE)NVD
An authentication bypass using an alternate path or channel [CWE-288] in Fortinet FortiOS version 7.2.0 through 7.2.1 an
FortiOS and FortiProxy contain an authentication bypass via the Node.js websocket module allowing unauthenticated remote
A out-of-bounds write in Fortinet FortiOS versions 7.4.0 through 7.4.2, 7.2.0 through 7.2.6, 7.0.0 through 7.0.13, 6.4.0
A heap-based buffer overflow vulnerability [CWE-122] in FortiOS version 7.2.4 and below, version 7.0.11 and below, versi
Fortinet FortiAnalyzer before 5.0.12 and 5.2.x before 5.2.5; FortiSwitch 3.3.x before 3.3.3; FortiCache 3.0.x before 3.0
Buffer overflow in the Cookie parser in Fortinet FortiOS 4.x before 4.1.11, 4.2.x before 4.2.13, and 4.3.x before 4.3.9
Remote code execution in Fortinet FortiOS (6.4 through 7.6.3) and FortiSwitchManager (7.0.x/7.2.x) lets an attacker run
Path traversal vulnerability in Fortinet FortiOS, FortiProxy, FortiPAM, and FortiSwitchManager allows authenticated admi
Cross-site scripting (XSS) vulnerability in the sslvpn login page in Fortinet FortiOS 5.2.x before 5.2.3 allows remote a
FortiOS and FortiProxy contain an authentication bypass allowing unauthenticated attackers with knowledge of upstream/do
An Exposure of Sensitive Information to an Unauthorized Actor vulnerability [CWE-200] vulnerability in Fortinet FortiOS
Use of a hard-coded cryptographic key to cipher sensitive data in FortiOS configuration backup file may allow an attacke
GitHub PoC
Exploit-DB