Fortinet sounds the alarm over actively exploited FortiMail zero-day

Fortinet is warning customers to lock down FortiMail after attackers started exploiting a critical bug that lets them write files to vulnerable systems without logging in. The flaw, tracked as CVE-2026-104286, carries a CVSS score of 9.8 and affects multiple versions of Fortinet's email security platform. Fortinet describes the vulnerability as a combination of path traversal and improper handling of null characters in FortiMail's web interface.