Fortinet warns of critical FortiMail flaw exploited in zero-day attacks

Fortinet is warning customers of a critical FortiMail vulnerability, tracked as CVE-2026-104286, that is being actively exploited in zero-day attacks to execute unauthorized code or commands on vulnerable devices.

The vulnerability is rated critical, with a CVSS score of 9.8, and affects the FortiMail management interface.

"An Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') [CWE-22] and Improper Neutralization of NULL Byte or NULL Character [CWE-158] vulnerability may allow an unauthenticated attacker to write arbitrary files on the underlying system via crafted HTTP or HTTPS requests," Fortinet said in an advisory published Thursday.

Gwendal Guégniaud of Fortinet's Product Security team discovered the vulnerability internally, and it affects FortiMail 8.0.0 through 8.0.1, FortiMail 7.6.0 through 7.6.6, FortiMail 7.4.0 through 7.4.8, and FortiMail 7.2.0 through 7.2.9.