What is CVE-2021-24020?

CVE-2021-24020 is a high-severity vulnerability in Fortinet Fortimail, classified under Improper Verification of Cryptographic Signature. CVSS score: 7.5/10. Published 2021-07-09.

How severe is CVE-2021-24020?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Fortinet Fortimail

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.

Published 2021-07-09 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.5th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Fortinet Fortimail
Fortinet Fortimail — versions FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

fortiguard.com/advisory/FG-IR-21-027 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-24020?: CVE-2021-24020 is a high-severity vulnerability in Fortinet Fortimail, classified under Improper Verification of Cryptographic Signature. CVSS score: 7.5/10. Published 2021-07-09.
How severe is CVE-2021-24020?: High severity. CVSS v3 base score is 7.5 out of 10.