The US Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2026-104286, a Fortinet FortiMail Path Traversal Vulnerability, to its Known Exploited Vulnerabilities (KEV) catalog on October 1, 2026. CISA adds a flaw to the catalog when it has reliable evidence that attackers are exploiting it in the wild.
What CISA says
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.
— CISA KEV catalog entry for CVE-2026-104286
Key facts
| CVE | CVE-2026-104286 |
|---|---|
| Vendor / product | Fortinet FortiMail |
| Added to KEV | October 1, 2026 |
| Federal deadline | October 4, 2026 |
| Known ransomware use | Unknown |
| Weakness (CWE) | CWE-22, CWE-158 |
| CISA forensic triage | Yes |
Who has to act, and by when
US federal civilian executive branch agencies are required to remediate the vulnerability by October 4, 2026. CISA urges all organizations to prioritize KEV-listed flaws as part of their vulnerability management.
CISA’s required action for this entry:
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.
References
- CISA Known Exploited Vulnerabilities Catalog https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- NIST NVD — CVE-2026-104286 https://nvd.nist.gov/vuln/detail/CVE-2026-104286
- fortiguard.fortinet.com https://fortiguard.fortinet.com/psirt/FG-IR-26-175
- www.cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- www.cisa.gov https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk