Executive Summary
CVE-2026-39808 is a second OS command injection vulnerability (CWE-78) in Fortinet FortiSandbox, disclosed alongside CVE-2026-25089 and added to CISA’s Known Exploited Vulnerabilities catalogue on the same date (16 July 2026). Like CVE-2026-25089, it allows an unauthenticated attacker to execute unauthorized system commands via crafted HTTP requests. The two vulnerabilities are documented under separate Fortinet PSIRT advisories — FG-IR-26-100 for this CVE and FG-IR-26-141 for CVE-2026-25089 — indicating they affect different code paths in the FortiSandbox application.
The simultaneous addition of two unauthenticated command injection CVEs in the same product to CISA KEV signals that FortiSandbox has been under active attack, with multiple entry points being exploited. Organizations running FortiSandbox must patch against both vulnerabilities; addressing only one leaves the second exploitable.
CISA’s BOD 26-04 remediation deadline for CVE-2026-39808 is 19 July 2026.
Affected Versions
CVE-2026-39808 affects FortiSandbox. The Fortinet PSIRT advisory at https://fortiguard.fortinet.com/psirt/FG-IR-26-100 specifies the exact affected version branches and the minimum patched version for each.
Unlike CVE-2026-25089, the CISA KEV description for CVE-2026-39808 references FortiSandbox only, without explicitly listing the cloud and PaaS variants. Organizations using FortiSandbox Cloud or FortiSandbox PaaS should consult Fortinet directly to determine if FG-IR-26-100 scope extends to those platforms.
Treat both FortiSandbox CVEs (CVE-2026-25089 and CVE-2026-39808) as affecting the same product family until Fortinet’s advisories definitively scope otherwise.
Vulnerability Details
CVE-2026-39808 shares the same vulnerability class (CWE-78, OS command injection) as CVE-2026-25089, but the distinct PSIRT identifiers confirm separate vulnerable code paths. Two command injection flaws in the same product often arise from:
- Different functional areas of the application — for example, one vulnerability in file analysis request handling and another in reporting or system management functions
- Different input vectors — one via request body parameters, another via HTTP headers or URL path components
- Independent development teams implementing similar functionality without shared input validation libraries
The practical implication: a patch for one vulnerability does not remediate the other. Each flaw has its own vulnerable function, its own attack path, and its own patch commit. Organizations that applied a partial update targeting only CVE-2026-25089 remain exposed to CVE-2026-39808 if they did not install the full remediation package.
The exploitation mechanics are the same class as CVE-2026-25089. An attacker crafts an HTTP request with shell metacharacters embedded in the parameter or field affected by this specific CVE. The FortiSandbox web application passes this input to a shell command without sanitisation, and the injected commands execute on the host OS with the privileges of the web server process — elevated in a sandbox product.
Exploitation in the Wild
Both FortiSandbox command injection CVEs were added to CISA KEV simultaneously, suggesting they were discovered in the context of the same exploitation activity. Attackers probing FortiSandbox instances likely identified multiple injectable parameters and multiple exploitable endpoints during the same campaign, accounting for why two separate CVEs reached the KEV threshold at the same time.
The threat actors most likely to exploit FortiSandbox vulnerabilities are those who specifically target security operations infrastructure:
- Nation-state actors seeking counterintelligence value (understanding what a target organization’s security tools can detect)
- Operators focused on disabling security controls before deploying ransomware or conducting destructive operations
- APT groups that have specifically targeted Fortinet products in previous campaigns
FortiSandbox’s position in the analysis pipeline means that compromising it gives attackers visibility into what samples the security team is analyzing, potentially allowing them to adjust malware to evade the specific detection capabilities in use. This intelligence value is distinct from the network access value of a typical infrastructure compromise.
Patch and Remediation
Apply the full patch package covering both CVE-2026-25089 (FG-IR-26-141) and CVE-2026-39808 (FG-IR-26-100). Verify against the Fortinet Support portal that the installed FortiSandbox version is patched against both PSIRT advisories, not just one.
After applying the update, confirm the installed version against both advisory documents before removing the CVEs from your tracking queue.
If immediate patching is not possible, apply the same interim mitigations as CVE-2026-25089:
- Restrict management interface access to specific administrative source IPs via firewall rules
- Disable remote administration access that is not operationally required
- Place FortiSandbox management interfaces behind a VPN or jump host requiring authentication before the management interface is accessible
Do not assume that mitigating CVE-2026-25089 also mitigates CVE-2026-39808. They are separate vulnerabilities requiring separate patches.
Detection
Detection guidance for CVE-2026-39808 follows the same pattern as CVE-2026-25089, applied to the different affected endpoint:
Broad signature: Any HTTP request to the FortiSandbox management interface containing shell metacharacters (;, &&, |, `, $(...)) in parameter values, headers, or URL paths should be flagged for investigation.
Process anomalies: Unexpected child processes of the FortiSandbox web server process, particularly command interpreters (sh, bash) or network utilities (wget, curl, nc), indicate successful injection regardless of which CVE was exploited.
Dual vulnerability coverage: IDS/IPS signatures for FortiSandbox command injection should be applied broadly across all FortiSandbox management endpoints, not just the endpoints associated with either individual CVE. Attackers exploit whichever path works; detection should cover the full attack surface.
Forensics: If exploitation is suspected, preserve full HTTP access logs from the FortiSandbox management interface and system process creation logs before applying the patch. The commands injected and the subsequent attacker actions (establishing persistence, lateral movement) are reconstructable from these log sources.
Correlation: Cross-reference FortiSandbox logs with network logs for outbound connections from the FortiSandbox management host. Reverse shell establishment and download cradle activity from the FortiSandbox host, correlated with recent inbound management interface requests, provides high-confidence exploitation confirmation.