Known exploited · Fortinet
CVE-2026-104286: Fortinet FortiMail Path Traversal Vulnerability
What it is
Fortinet FortiMail contains a path traversal and an improper neutralization of NULL byte or NULL character vulnerability that may allow an unauthenticated attacker to write arbitrary files on the underlying system via crafted HTTP or HTTPS requests.
- Vendor
- Fortinet
- Product
- FortiMail
- Added to KEV
- October 1, 2026
- CISA due date
- October 4, 2026
- Ransomware use
- Unknown
What CISA requires
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Forensic triage
Yes
What to do now
- Find every instance of FortiMail you run, including the forgotten ones, and check its version against the vendor advisory.
- Apply the vendor's fix or mitigation, before October 4, 2026 if you are bound by CISA's deadline, sooner if it faces the internet.
- Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
- Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops path traversal attempts.
References
The Dome
Block it at the edge while you patch
The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops path traversal attempts before they reach your application.
See the DomeT Academy
Train the engineers who fix it
Security engineering on real hosts in the browser, every objective checked on the machine. The first two lessons of Linux 1 are free.
Start freeSource: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.