How severe is CVE-2021-36166?

CVE-2021-36166 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-36166 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-36166?

CVE-2021-36166 primarily affects Fortinet Fortimail. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-36166?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-36166 published?

CVE-2021-36166 was published on 2022-03-01 and last updated on 2026-06-17.

CVE-2021-36166

CVE-2021-36166 is a critical-severity vulnerability in Fortinet Fortimail with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-330.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 1% (70th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-330
Affected product: Fortinet Fortimail
Published: 2022-03-01
Last modified: 2026-06-17

Description

An improper authentication vulnerability in FortiMail before 7.0.1 may allow a remote attacker to efficiently guess one administrative account's authentication token by means of the observation of certain system's properties.

Frequently asked questions

What is CVE-2021-36166?: An improper authentication vulnerability in FortiMail before 7.0.1 may allow a remote attacker to efficiently guess one administrative account's authentication token by means of the observation of certain system's properties.
How severe is CVE-2021-36166?: CVE-2021-36166 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-36166 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-36166?: CVE-2021-36166 primarily affects Fortinet Fortimail. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-36166?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-36166 published?: CVE-2021-36166 was published on 2022-03-01 and last updated on 2026-06-17.

References

https://fortiguard.com/psirt/FG-IR-21-028

Affected products (2)

cpe:2.3:a:fortinet:fortimail:*:*:*:*:*:*:*:*
cpe:2.3:a:fortinet:fortimail:7.0.0:*:*:*:*:*:*:*

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