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Upgrade to ProDetect Fortinet FortiSandbox OS Command Injection (CVE-2026-39808) in Splunk
Detects potential exploitation of CVE-2026-39808, an OS command injection vulnerability (CWE-78) in Fortinet FortiSandbox that allows an authenticated or unauthenticated attacker to execute arbitrary OS commands via crafted requests to the FortiSandbox management interface. This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and is subject to BOD 26-04 remediation timelines. Detection focuses on anomalous shell/command execution patterns originating from FortiSandbox processes, suspicious HTTP requests to the management interface containing shell metacharacters, and unexpected child processes spawned by FortiSandbox web/API services observed via syslog, proxy, or EDR telemetry on adjacent/monitoring hosts.
MITRE ATT&CK
- Tactic
- Initial Access Execution
SPL Detection Query
index=network_proxy OR index=firewall sourcetype=cef OR sourcetype=fortinet:fortisandbox
| eval decoded_url=urldecode(request_url)
| regex decoded_url="(;|\||&&|`|\$\(|%0a|%0d|/bin/(ba)?sh|wget\s|curl\s|nc\s|chmod\s\+x)"
| where match(decoded_url, "(?i)(/api|/sys|/cgi-bin)")
| table _time, src_ip, dest_ip, decoded_url, http_method, status
| sort -_timeSearches Splunk-ingested firewall/proxy/CEF logs for requests to FortiSandbox API or management endpoints containing shell metacharacters or reverse-shell/download primitives indicative of OS command injection exploitation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Authorized vulnerability scanning traffic
- Encoded parameters from legitimate file-upload workflows
- Load balancer health checks with unusual query strings
Other platforms for CVE-2026-39808
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate command injection payload via HTTP request
Expected signal: Proxy/firewall log entry with RequestURL containing ';id' directed at a lab FortiSandbox API endpoint
- Test 2Simulate reverse-shell download attempt via injected command
Expected signal: Decoded URL parameter containing '&&wget' pattern logged in proxy/CEF logs; potential outbound connection to LAB-C2 in network logs
- Test 3Simulate suspicious child process spawn from FortiSandbox-named parent
Expected signal: EDR process-creation event showing ParentBaseFileName 'fsav_httpd' spawning /bin/bash with CommandLine containing the test string
References (4)
- https://fortiguard.fortinet.com/psirt/FG-IR-26-100
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-39808
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