CVE-2026-39808: Fortinet FortiSandbox OS Command Injection Vulnerability

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Yes, if you run Fortinet FortiSandbox. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-07-16, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-07-19; treat that as the outer limit, not the target.
• EPSS 47.4%, percentile 99: FIRST’s model estimates a 47.4% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Editorial verdict: Act now. FortiSandbox: Two Exploited Pre-Auth Command Injections — If any FortiSandbox runs 4.2, 4.4 below 4.4.9 or 5.0 below 5.0.6, upgrade now and check it for compromise: both bugs need no login, one has a public exploit, and attacks began in June.

What it is

A improper neutralization of special elements used in an os command ('os command injection') vulnerability in Fortinet FortiSandbox 4.4.0 through 4.4.8 may allow attacker to execute unauthorized code or commands via

CISA’s summary

Fortinet FortiSandbox contains an OS command injection vulnerability that could allow an unauthenticated attacker to execute unauthorized code or commands via crafted HTTP requests.

Weakness type: CWE-78.

Product: Fortinet FortiSandbox · Assigned by: fortinet · Published: 2026-04-14

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: added 2026-07-16; federal due date 2026-07-19. Known ransomware use: Unknown.
• CISA 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). 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.
• CISA SSVC assessment: exploitation active, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 47.36% probability of exploitation activity in the next 30 days; percentile 99.

Timeline

• 2026-04-14 — CVE record published by fortinet
• 2026-04-14 — erroneo.us brief: FortiSandbox: Two Exploited Pre-Auth Command Injections
• 2026-07-16 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2026-07-17 — CVE record last updated
• 2026-07-19 — CISA remediation deadline for US federal agencies

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (fortiguard.fortinet.com) fortiguard.fortinet.com

Vulnerability records

1. CVE.org record CVE-2026-39808 cve.org
2. NVD entry CVE-2026-39808 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
2. Listed in CISA KEV notes (cisa.gov) cisa.gov
3. Listed in CISA KEV notes (cisa.gov) cisa.gov

Other references from the CVE record and advisory

1. github.com github.com

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