CVE-2021-36173

Name: CVE-2021-36173
Creator: NVD / NIST
Published: 2021-12-08T19:15:09.787+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 1.44%

Last modified Jun 17, 2026

CVE-2021-36173 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. A heap-based buffer overflow in the firmware signature verification function of FortiOS versions 7.0.1, 7.0.0, 6.4.0 through 6.4.6, 6.2.0 through 6.2.9, and 6.0.0 through 6.0.13 may allow an attacker to execute arbitrary code via specially crafted installation images.. EPSS estimates a 1.44% chance of exploitation in the next 30 days.

Description

A heap-based buffer overflow in the firmware signature verification function of FortiOS versions 7.0.1, 7.0.0, 6.4.0 through 6.4.6, 6.2.0 through 6.2.9, and 6.0.0 through 6.0.13 may allow an attacker to execute arbitrary code via specially crafted installation images.

Metrics

CVSS 3.1

8.8/10

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

EPSS Probability

1.44%

69.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Fortinet	Fortios	>= 6.0.0, <= 6.0.13
Fortinet	Fortios	>= 6.2.0, <= 6.2.9
Fortinet	Fortios	>= 6.4.0, <= 6.4.6
Fortinet	Fortios	7.0.0
Fortinet	Fortios	7.0.1

References

https://fortiguard.com/advisory/FG-IR-21-115Patch, Vendor Advisory
https://fortiguard.com/advisory/FG-IR-21-115Patch, Vendor Advisory

Timeline

Published: Dec 8, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-36173?

How severe is CVE-2021-36173?

CVE-2021-36173 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 1.44% probability of exploitation in the next 30 days.

How do I fix CVE-2021-36173?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-36173?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST