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Fortinet reports that attackers are exploiting CVE-2026-104286 in the wild. The critical, unauthenticated flaw affects FortiMail’s publicly reachable web GUI and can let a remote attacker write arbitrary files to the system. Administrators should identify their FortiMail branch and move to its fixed release; devices on the 7.2 branch should be upgraded to 7.4 or later.
What the FortiMail vulnerability does
MS-ISAC describes CVE-2026-104286 as a path-traversal vulnerability combined with NULL byte injection. An attacker can send crafted HTTP or HTTPS requests to FortiMail’s publicly reachable graphical user interface without logging in. Successful exploitation can write arbitrary files to the underlying system; that access could potentially lead to arbitrary command execution, but command execution is not established as an outcome in every incident.
The Canadian Centre for Cyber Security reported on October 1, 2026, that CISA had added the vulnerability to its Known Exploited Vulnerabilities (KEV) catalog. The government advisory says, “Fortinet indicates that CVE-2026-104286 is exploited in the wild.” Canadian Centre for Cyber Security advisory AV26-989; MS-ISAC advisory 2026-108.
Which FortiMail versions are affected, and what should you install?
The Canadian Centre for Cyber Security lists these fixed-release thresholds. MS-ISAC enumerates the affected ranges shown below. Confirm Fortinet’s current upgrade path and the appropriate target release for your specific deployment before scheduling an upgrade.
#1 Best Overall
- Fortinet FortiMail-VM virtual appliance for all supported platforms. 1 x vCPU cores
- Fortinet SW FML-VM01
- Manufacturer Part: FML-VM01
| Installed branch | Affected versions listed by MS-ISAC | Upgrade guidance from the Canadian Centre for Cyber Security |
|---|---|---|
| FortiMail 8.0 | 8.0.0–8.0.1 | 8.0.2 or later |
| FortiMail 7.6 | 7.6.0–7.6.6 | 7.6.7 or later |
| FortiMail 7.4 | 7.4.0–7.4.8 | 7.4.9 or later |
| FortiMail 7.2 | 7.2.0–7.2.9 | Upgrade to branch 7.4 or later |
Sources: Canadian Centre for Cyber Security advisory AV26-989 and MS-ISAC advisory 2026-108. The listed ranges and thresholds are advisory guidance, not a substitute for checking Fortinet’s current release and upgrade-path instructions for the device.
Quick Recap
Best Value
- Fortinet FortiMail-VM virtual appliance for all supported platforms. 2 x vCPU cores
- Fortinet SW FML-VM02
- Manufacturer Part: FML-VM02
Rank #4
- Fortinet FortiMail-VM virtual appliance for all supported platforms. 4 x vCPU cores
- Fortinet SW FML-VM04
- Manufacturer Part: FML-VM04
Rank #3
- FortiMail is a top-rated secure email gateway that stops volume-based and targeted cyber threats to help secure the dynamic enterprise attack surface, prevents the loss of sensitive data and helps
- High performance physical and virtual appliances deploy on-site or in the public cloud to serve any size organization - from small businesses to carriers, service providers, and large enterprises
- Threat Prevention Powerful antispam and antimalware, are complemented by advanced techniques like outbreak protection, content disarm and reconstruction, sandbox analysis, impersonation detection
- Data Protection Robust data loss prevention, identitybased email encryption and archiving help prevent the inadvertent loss of sensitive information and maintain compliance with corporate and
- Security Fabric Integration Integrations with Fortinet products as well as third-party components help customers adopt a proactive approach to security by sharing IoCs across a seamless Security
Rank #2
- FortiMail is a top-rated secure email gateway that stops volume-based and targeted cyber threats to help secure the dynamic enterprise attack surface, prevents the loss of sensitive data and helps
- High performance physical and virtual appliances deploy on-site or in the public cloud to serve any size organization - from small businesses to carriers, service providers, and large enterprises
- Threat Prevention Powerful antispam and antimalware, are complemented by advanced techniques like outbreak protection, content disarm and reconstruction, sandbox analysis, impersonation detection
- Data Protection Robust data loss prevention, identitybased email encryption and archiving help prevent the inadvertent loss of sensitive information and maintain compliance with corporate and
- Security Fabric Integration Integrations with Fortinet products as well as third-party components help customers adopt a proactive approach to security by sharing IoCs across a seamless Security
What administrators should do now
- Check installed version and branch. Inventory FortiMail appliances and identify whether any run a version in the affected ranges above, including internet-facing systems.
- Plan the vendor-supported upgrade. Use Fortinet’s current upgrade path and confirm the precise target release for the appliance and deployment. For 7.2 installations, the cited guidance is to move to branch 7.4 or later.
- Investigate possible compromise if warranted. Because exploitation is reported in the wild, follow your organization’s incident-response process if an affected system may have been exposed or shows suspicious activity. The cited advisories do not provide detailed indicators of compromise.
- Do not assume an unverified workaround closes the risk. The reviewed advisories recommend vendor updates but do not specify a temporary workaround or compensating configuration control for systems that cannot yet be upgraded.
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