Critical Zero-Day Vulnerability in FortiMail Allows Unauthenticated File Writes

Fortinet disclosed a critical zero-day vulnerability in its FortiMail email security product that is already being exploited in attacks. The flaw, tracked as CVE-2026-104286, affects the graphical user interface component and stems from improper sanitization of path traversal and NULL byte sequences. Attackers can craft malicious HTTP requests to write arbitrary files to the system without authentication. The vulnerability received a CVSS v3.1 base score of 9.8, classifying it as Critical. Fortinet discovered the issue internally but has also received reports of active exploitation. Planned patches include FortiMail 8.0.2, 7.6.7, and 7.4.9, while users on the 7.2 branch are advised to migrate to 7.4 or later.

Security NEXTTranslated from Japanese

Read at source

Fortinet has disclosed a critical zero-day vulnerability in its FortiMail email security product that is already being actively exploited in the wild.

The company published a security advisory on October 1, 2026, detailing the flaw tracked as CVE-2026-104286. The issue resides in the graphical user interface component and results from inadequate neutralization of path traversal sequences and NULL bytes or NULL characters.

Successful exploitation allows an unauthenticated attacker to craft malicious HTTP requests and write arbitrary files to the underlying system. The vulnerability carries a CVSS v3.1 base score of 9.8 and is rated Critical, the highest severity level.

Although Fortinet discovered the flaw internally, the company confirmed reports of real-world exploitation. It plans to release fixed versions including FortiMail 8.0.2, FortiMail 7.6.7, and FortiMail 7.4.9. Organizations running the FortiMail 7.2 branch are instructed to migrate to the 7.4 release or newer.

Meridian digestThe week's most consequential security stories, distilled into one briefing.See the digest

More in Vulnerabilities & Exploits

Telegram for Android Patches Voice Call Vulnerability Enabling Code Execution
Yandex Patches Millions of Stations After eMudhra Certificate Keys Compromised
Cisco ASA and FTD Face DoS Vulnerability in SSL VPN Already Exploited in the Wild