CVE-2021-24020: Fortinet FortiMail

Critical severity, CVSS 9.8. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Fortinet FortiMail: from 6.2.0, up to and including 6.2.7; from 6.4.0, before 6.4.5 (fixed in 6.4.5)

Published 2021-07-09. Last modified 2026-06-17.