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. An unauthenticated attacker can exploit it using specially crafted HTTP or HTTPS requests to write arbitrary files to the underlying system. Writing files to certain locations could allow an attacker to execute code or commands on the appliance. Fortinet says the flaw affects FortiMail versions 8.0.0 through 8.0.1, 7.6.0 through 7.6.6, 7.4.0 through 7.4.8, and 7.2.0 through 7.2.9. The vendor's advisory says CVE-2026-104286 "is being exploited in the wild," although it doesn't say when the attacks began, who is behind them, or how many customers may have been compromised. …