CVE-2021-36166Network attack vector

Administrative account takeover via predictable authentication token

Published Mar 1, 2022 · Updated Oct 25, 2024

Improper authentication in Fortinet FortiMail before 7.0.1 allows remote attackers to guess an administrator's authentication token. The authentication flow uses observable system properties in a way that makes one administrative account's token efficiently guessable, but Fortinet has not disclosed the affected endpoint or token-generation routine. Network access to the affected authentication service is sufficient, and a recovered token grants that administrative account's access.

CVSS severity9.8
Critical
EPSS probability1.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Fortinet FortiMail before 7.0.1 allows remote attackers to guess an administrator's authentication token. The authentication flow uses observable system properties in a way that makes one administrative account's token efficiently guessable, but Fortinet has not disclosed the affected endpoint or token-generation routine. Network access to the affected authentication service is sufficient, and a recovered token grants that administrative account's access.

The record

CVE
CVE-2021-36166
Published
Mar 1, 2022
Updated
Oct 25, 2024
Vendor
Fortinet
Product
FortiMail
Classifications
CWE-287, CWE-330, T1110
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 1, 2022CVE 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=FortiMail before 7.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fortinet · FortiMailversion=FortiMail before 7.0.1

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8FortinetCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
CWE-330Use of Insufficiently Random Values
T1110Brute Force

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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