🔴 Critical FortiMail Zero-Day Flaw Exploited in Attacks Allows Unauthenticated Arbitrary File Writes

The U.S. Cybersecurity and Infrastructure Security Agency (CISA), on Thursday, added a critical security flaw impacting Fortinet FortiMail to its Known Exploited Vulnerabilities (KEV) catalog, following reports of active exploitation.

The vulnerability, tracked as CVE-2026-104286 (CVSS score: 9.8), allows unauthenticated attackers to write arbitrary files on the underlying system.

"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.