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CVE-2026-104286

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Fortinet FortiMail. For every flaw being used in attacks, see Exploited flaws; for Fortinet’s, see Fortinet flaws being used in attacks.

CVE-2026-104286 is a security flaw in Fortinet FortiMail, Fortinet’s business security equipment. Attackers can reach parts of Fortinet FortiMail that should be locked to them from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 1 Oct 2026.[1]

Fortinet FortiMail is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fortinet has published a fix or advice.

Description

CISA calls it a path traversal in Fortinet FortiMail. In its words: “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.”[1]

The CVE record adds: “An improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiMail 8.0.0 through 8.0.1, FortiMail 7.6.0 through 7.6.6, FortiMail 7.4.0 through 7.4.8, FortiMail 7.2.0 through 7.2.9, FortiMail 7.0 all versions may allow an unauthenticated attacker to write arbitrary files on the underlying system via crafted HTTP or HTTPS requests.”[2]

The underlying weakness is path traversal (CWE-22), CWE-158, in MITRE’s list of common software weaknesses.

It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by the organisation that published the CVE using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Fortinet’s advisory has them[3]. CISA names the product as Fortinet FortiMail.

Most families won’t have Fortinet FortiMail; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 1 Oct 2026, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 4 Oct 2026 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 5%. That’s in the top 9% of the flaws it scores.[4]

CISA assesses it as automatable: attackers can run it against many targets at once.

CISA doesn’t say who was attacked, or how.

Fix

Fortinet has published a fix or advice.[3] CISA’s required action: “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).”[1]

  1. Check whether you use it.Fortinet FortiMail is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 4 Oct 2026 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 5%.[4]

See also

Other Fortinet flaws

  • CVE-2025-61624, Fortinet products: path traversal ·
  • CVE-2025-25249, Fortinet products: heap-based buffer overflow ·
  • CVE-2025-68686, Fortinet FortiOS: exposure of sensitive information to an unauthorized actor ·
  • CVE-2026-39808, Fortinet FortiSandbox: OS command injection ·
  • CVE-2026-25089, Fortinet FortiSandbox: OS command injection ·

Other path traversal flaws

  • CVE-2021-3199, ONLYOFFICE Docs: server path traversal ·
  • CVE-2026-93616, Check Point products: path traversal ·
  • CVE-2026-66384, JFrog Artifactory: improper limitation of a pathname to a restricted directory ·
  • CVE-2026-59310, Broadcom VMware vCenter: path traversal ·
  • CVE-2026-48282, Adobe ColdFusion: path traversal ·

Every Fortinet flaw on CISA’s list · Everything added in October 2026

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Fortinet FortiMail Path Traversal Vulnerability”. Known Exploited Vulnerabilities Catalog, added 1 Oct 2026.
  2. ^ National Institute of Standards and Technology. “CVE-2026-104286 Detail”. National Vulnerability Database, published 1 Oct 2026.
  3. ^ Fortinet. Advisories and fixes: fortiguard.fortinet.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.046, percentile 91.6, 31 Oct 2026.
  5. CVE Program. “CVE-2026-104286”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.