CVE-2026-104286: Fortinet FortiMail exploitation alert

CVE-2026-104286: what changed

CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 2026-10-01. Inclusion indicates evidence of exploitation; it does not establish that your own systems have been compromised.

Affected product

Fortinet FortiMail. Confirm affected versions against the vendor advisory.

CISA description

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.

Recommended response

Inventory affected deployments, check vendor guidance for fixes or mitigations, and verify the update was applied. Review available logs and incident-response guidance when exploitation is suspected.

Catalog context

CISA lists a remediation due date of 2026-10-04. Federal directive deadlines have a defined scope; other organizations should prioritize according to their exposure and risk. Ransomware campaign use is listed as unknown; “unknown” does not mean exploitation is absent.

Sources

• CISA Known Exploited Vulnerabilities catalog
• CVE-2026-104286 reference

Automated security brief based on CISA catalog data. Catalog addition date: 2026-10-01.