CVE-2020-12812 — Fortinet FortiOS SSL VPN Improper Authentication Vulnerability

In brief

Severity · CVSS: Critical9.8CVSS 3.1, Critical
EPSS: 49%
CISA KEV: Known exploited, listed since 3 Nov 2021
CERT-FR: No advisory or alert referenced in the catalog
Vendor: Fortinet
Published · Modified: 24 Jul 2020 · 12 Aug 2026
Last verified: 1 Oct 2026 at 09:30 UTC

Summary

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.

Weakness: CWE-178, CWE-287

Title, description and the vendor's statements are quoted from the CVE record; a vendor's advisory is summarised in Patcharo's words, with a link.

Affected and fixed versions

Per product and release branch, as the vendor's CVE record and official advisory state them. A fixed release is shown only when a document names it: the vendor's, or CERT-FR's for Check Point, with its source.

No precise fixed release is published in the sources Patcharo follows.

Fortinet FortiOS

Source: CVE-2020-12812

—
Affected versionsFortiOS 6.4.0, 6.2.0 to 6.2.3, 6.0.9 and below
First fixed releaseNot published in the sources followed

No precise fixed release is published for this product in the sources Patcharo follows.

Remediation

Vendor guidance

CISA KEV required action

Apply updates per vendor instructions.

CISA due date: 3 May 2022

SourceCISA KEV

Vendor advisory

The vendor has published an advisory for this CVE: check it for fixed releases and mitigations.

SourceFortiGuard FG-IR-19-283

Last verified 1 Oct 2026 at 09:30 UTC

Known exploitation

Added to CISA KEV on 3 Nov 2021

Federal remediation due date: 3 May 2022

Known use in ransomware campaigns

The CISA required action is shown under Remediation.

49% probability of exploitation in the next 30 days (percentile 99%).

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CERT-FR

No CERT-FR advisory or alert of the last two years references this CVE, for the vendors Patcharo covers.

Timeline

24 Jul 2020Published by the source
3 Nov 2021Added to CISA KEV
3 May 2022CISA remediation due date
12 Aug 2026Source record last modified
28 Sept 2026EPSS score computed
1 Oct 2026Last verified by Patcharo

Official sources

Fortinet (CVE record)retrieved 1 Oct 2026 at 09:30 UTC
CISA Known Exploited Vulnerabilitiesretrieved 1 Oct 2026 at 09:28 UTC
NVDretrieved 27 Sept 2026 at 23:44 UTC
FIRST EPSSretrieved 29 Sept 2026 at 03:17 UTC
FortiGuard FG-IR-19-283retrieved 1 Oct 2026 at 09:30 UTC

References

Fortinet · CISA Known Exploited Vulnerabilities · NVD · FIRST EPSS · FortiGuard FG-IR-19-283

How Patcharo reads this

Affected and fixed releases come from the vendor's structured statements and are matched against exact versions; CVSS from NVD, exploitation from CISA KEV and the vendor's own advisory, probability from FIRST EPSS. Missing data stays Unknown and never becomes Not affected.

Read the methodology Read the guide: FortiOS version numbering: branches, patch releases and the Feature and Mature labels