How severe is CVE-2021-24020?

CVE-2021-24020 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-24020 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-24020?

CVE-2021-24020 affects Fortinet Fortimail. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-24020?

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.

When was CVE-2021-24020 published?

CVE-2021-24020 was published on 2021-07-09 and last updated on 2026-06-17.

CVE-2021-24020

CVE-2021-24020 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-347.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.5
EPSS exploit prediction: 1% (45th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-347
Affected product: Fortinet Fortimail
Published: 2021-07-09
Last modified: 2026-06-17

Description

A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to tamper with signed URLs by appending further data which allows bypass of signature verification.

Frequently asked questions

What is CVE-2021-24020?: A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to tamper with signed URLs by appending further data which allows bypass of signature verification.
How severe is CVE-2021-24020?: CVE-2021-24020 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-24020 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (45th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-24020?: CVE-2021-24020 affects Fortinet Fortimail. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-24020?: 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.
When was CVE-2021-24020 published?: CVE-2021-24020 was published on 2021-07-09 and last updated on 2026-06-17.

References

https://fortiguard.com/advisory/FG-IR-21-027

Affected products (1)

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

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