Fortinet has issued a warning about a critical zero-day vulnerability in FortiMail, tracked as CVE-2026-104286 (CVSS 9.8), which is being actively exploited in the wild. The flaw allows unauthenticated attackers to write arbitrary files to the underlying system, potentially leading to remote code execution. CISA has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog, urging immediate patching. Organizations using FortiMail should prioritize applying the available security updates to prevent compromise.