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Upgrade to ProDetect Fortinet FortiSandbox OS Command Injection (CVE-2026-39808) in Elastic Security
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
Elastic Detection Query
network where event.dataset in ("fortinet.fortisandbox", "proxy.log") and
url.path : ("*api*", "*sys*", "*cgi-bin*") and
(url.original : "*;*" or url.original : "*|*" or url.original : "*&&*" or url.original : "*%60*" or url.original : "*wget*" or url.original : "*curl*" or url.original : "*/bin/sh*" or url.original : "*/bin/bash*")Elastic EQL rule to detect HTTP requests toward FortiSandbox API/system endpoints embedding shell metacharacters or download utilities associated with CVE-2026-39808 command injection.
Data Sources
Required Tables
False Positives & Tuning
- Automated scanning tools generating crafted payloads for testing
- Legitimate scripts embedding backticks or pipes in encoded query parameters
- Security research/purple-team validation traffic
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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