How severe is CVE-2021-26091?

CVE-2021-26091 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2021-26091 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26091?

CVE-2021-26091 affects Fortinet Fortimail. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-26091?

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

Does CVE-2021-26091 have an EU (EUVD) identifier?

Yes. CVE-2021-26091 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-12912.

When was CVE-2021-26091 published?

CVE-2021-26091 was published on 2025-03-24 and last updated on 2026-06-17.

CVE-2021-26091

CVE-2021-26091 is a high-severity vulnerability in Fortinet Fortimail with a CVSS 3.x base score of 7.5. 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-338.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2021-12912
Weakness: CWE-338
Affected product: Fortinet Fortimail
Published: 2025-03-24
Last modified: 2026-06-17

Description

A use of a cryptographically weak pseudo-random number generator vulnerability in the authenticator of the Identity Based Encryption service of FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to infer parts of users authentication tokens and reset their credentials.

Frequently asked questions

What is CVE-2021-26091?: A use of a cryptographically weak pseudo-random number generator vulnerability in the authenticator of the Identity Based Encryption service of FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to infer parts of users authentication tokens and reset their credentials.
How severe is CVE-2021-26091?: CVE-2021-26091 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2021-26091 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26091?: CVE-2021-26091 affects Fortinet Fortimail. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-26091?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2021-26091 have an EU (EUVD) identifier?: Yes. CVE-2021-26091 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-12912.
When was CVE-2021-26091 published?: CVE-2021-26091 was published on 2025-03-24 and last updated on 2026-06-17.

References

https://fortiguard.com/advisory/FG-IR-21-031

Affected products (1)

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

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