CVE-2020-12820

Under non-default configuration, a stack-based buffer overflow in FortiOS version 6.0.10 and below, version 5…

Severity: High8.8CVSS 3.1, High
EPSS: 0.89%
Published: 19 Dec 2024
Updated: 17 Jun 2026

Description

Title, description and vendor guidance are quoted from the source records.

Under non-default configuration, a stack-based buffer overflow in FortiOS version 6.0.10 and below, version 5.6.12 and below may allow a remote attacker authenticated to the SSL VPN to crash the FortiClient NAC daemon (fcnacd) and potentially execute arbitrary code via requesting a large FortiClient file name. We are not aware of proof of concept code successfully achieving the latter.

Weakness: CWE-121, CWE-787

Known exploited

Not listed in CISA KEV as of the last check.

Exploit prediction

0.89% probability of exploitation in the next 30 days (percentile 58%).

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

What the source states, per branch

Versions matched by Patcharo

Fortinet FortiOSSource: Fortinet (CVE record)

Branch	Affected	Fixed in
6.0	6.0.0 – 6.0.10	Fixed after 6.0.10
5.6	5.6.0 – 5.6.12	Fixed after 5.6.12

Versions not listed are stated unaffected by the vendor.

Workaround / Vendor remediation

Vendor remediation · FortiOS

Please upgrade to FortiOS versions 5.6.13 or above. Please upgrade to FortiOS versions 6.0.11 or above. FortiOS versions 6.2.0 and above are not impacted. FortiOS versions 6.4.0 and above are not impacted. Workaround: Please ensure that Fortiheartbeat and Endpoint-Compliance are not both enabled on the same interface. FortiHeartbeat and Endpoint-Compliance can be disabled on a particular interface by following the below CLI commands: config system interface edit interface set endpoint-compliance disable (<-- Disabled by default) set fortiheartbeat disable next end

References

https://fortiguard.fortinet.com/psirt/FG-IR-20-083(opens in a new tab)

Provenance

Every fact on this page comes from the sources below. Nothing is written by an AI.

Fortinet (CVE record): Fortinet (CVE record) · 27 Sept 2026, 23:46 UTC · Parser patcharo-cve5/1.1.0
NVD: NVD · 27 Sept 2026, 23:44 UTC · Parser patcharo-nvd/1.0.0
FIRST EPSS: FIRST EPSS · 27 Sept 2026, 23:46 UTC · Parser patcharo-epss/1.0.0

Last verified: 28 Sept 2026, 02:31 UTC