CVE-2021-36173

Arbitrary code execution via malformed firmware image

Published Dec 8, 2021 · Updated Oct 25, 2024

Heap overflow in FortiOS 6.0.0 through 6.0.13, 6.2.0 through 6.2.9, 6.4.0 through 6.4.6, and 7.0.0 through 7.0.1 allows attackers to execute code. The firmware signature verification function writes beyond a heap buffer while processing a crafted installation image, corrupting memory. A user must initiate installation of the attacker-supplied image; successful exploitation runs code with the verifier's privileges.

CVSS severity8.0
High
EPSS probability1.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap overflow in FortiOS 6.0.0 through 6.0.13, 6.2.0 through 6.2.9, 6.4.0 through 6.4.6, and 7.0.0 through 7.0.1 allows attackers to execute code. The firmware signature verification function writes beyond a heap buffer while processing a crafted installation image, corrupting memory. A user must initiate installation of the attacker-supplied image; successful exploitation runs code with the verifier's privileges.

The record

CVE
CVE-2021-36173
Published
Dec 8, 2021
Updated
Oct 25, 2024
Vendor
Fortinet
Product
FortiOS
Classifications
CWE-787, T1204.002
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Oct 25, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=FortiOS 7.0.1, 7.0.0, 6.4.0 through 6.4.6, 6.2.0 through 6.2.9, 6.0.0 through 6.0.13

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Fortinet · FortiOSversion=FortiOS 7.0.1, 7.0.0, 6.4.0 through 6.4.6, 6.2.0 through 6.2.9, 6.0.0 through 6.0.13

Published CVSS scores

8.0FortinetCVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
8.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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