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

A critical security flaw in Fortinet FortiMail is being actively exploited in attacks, prompting the US Cybersecurity and Infrastructure Security Agency to add it to its Known Exploited Vulnerabilities catalog. The vulnerability allows unauthenticated attackers to write arbitrary files on the underlying system. It has a high CVSS score of 9.8, indicating a severe impact. The issue is related to improper handling of certain operations. The vulnerability is identified as CVE-2026-104286. Active exploitation of this flaw has been reported, posing a significant risk to affected systems.