High severity · published Dec 8, 2021
CVE-2021-36173
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…
8.8
CVSS
1.5%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.5% · higher than 75% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FO
FortiOS · Fortinet
6.0.0 through 6.0.13; 6.2.0 through 6.2.9; 6.4.0 through 6.4.6; 7.0.0; 7.0.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-36173
CVE.org
https://www.cve.org/CVERecord?id=CVE-2021-36173
Patch
https://fortiguard.com/advisory/FG-IR-21-115
More from FortiOS
9.8
CVE-2026-24858
Fortinet Multiple Products Authentication Bypass Using an Alternate Path or Channel Vulnerability
9.8
CVE-2025-25249
Fortinet Multiple Products Heap-based Buffer Overflow Vulnerability
9.8
CVE-2025-59718
Fortinet Multiple Products Improper Verification of Cryptographic Signature Vulnerability
9.8
CVE-2024-55591
Fortinet FortiOS and FortiProxy Authentication Bypass Vulnerability
9.8
CVE-2024-23113
Fortinet Multiple Products Format String Vulnerability