Executive Summary
CVE-2026-25089 is a critical OS command injection vulnerability (CWE-78) in Fortinet FortiSandbox and its cloud variants. An unauthenticated attacker can execute arbitrary system commands on the FortiSandbox host by sending specially crafted HTTP requests to the management interface. No credentials are required.
CISA added CVE-2026-25089 to the Known Exploited Vulnerabilities catalogue on 16 July 2026, confirming active exploitation. The vulnerability affects the on-premises FortiSandbox appliance, FortiSandbox Cloud (managed cloud deployment), and FortiSandbox PaaS (platform-as-a-service offering) — meaning the exposed surface extends beyond on-premises deployments to cloud-hosted instances.
The vulnerability’s severity is compounded by its target: FortiSandbox is a security product designed to analyze and detonate suspicious files and URLs in isolation. Compromising the sandbox itself gives attackers access to the file samples submitted to it (potentially including sensitive malware intelligence and customer-submitted files), network visibility into sandbox analysis traffic, and in on-premises deployments, a foothold inside the security operations network segment.
Affected Versions
Based on the Fortinet PSIRT advisory FG-IR-26-141:
- FortiSandbox: Multiple versions prior to the patched release (see advisory for exact version ranges)
- FortiSandbox Cloud: Cloud-hosted instances not yet updated by Fortinet
- FortiSandbox PaaS: Platform-as-a-service instances pending vendor update
For exact affected version ranges, consult the Fortinet PSIRT advisory at https://fortiguard.fortinet.com/psirt/FG-IR-26-141. Fortinet’s versioning for FortiSandbox follows a major.minor.patch format; the advisory specifies which minor releases are affected and the minimum patched version for each branch.
Note that CVE-2026-39808 is a separate OS command injection vulnerability in FortiSandbox (PSIRT FG-IR-26-100) affecting a different code path. Organizations should treat both as requiring immediate remediation.
Vulnerability Details
OS command injection vulnerabilities occur when attacker-controlled input is concatenated into system command strings and passed to a shell without sanitisation. In web application contexts, this typically means an HTTP request parameter, header, or body field is passed directly to a system(), exec(), popen(), or equivalent function call.
FortiSandbox’s management interface processes HTTP requests that include administrative parameters — file submission paths, analysis configuration, reporting parameters, and system management functions. CVE-2026-25089 describes a code path reachable without authentication where request data is incorporated into a shell command without adequate sanitisation.
An attacker exploiting this vulnerability can inject shell metacharacters (;, &&, |, backticks, $(...)) into the affected parameter, causing the FortiSandbox host operating system to execute attacker-controlled commands. Because FortiSandbox runs with elevated privileges to perform sandbox analysis operations (including file execution and network monitoring), the commands typically execute with root or high-privilege access.
The attack requires only HTTP access to the FortiSandbox management interface. In typical deployments, the management interface is accessible from the SOC network and potentially exposed to management VLANs or restricted internet access for remote administration. Unauthenticated exploitation removes any protection provided by credential controls.
Fortinet’s PSIRT description confirms the attack vector: “unauthenticated attacker to execute unauthorized commands via specifically crafted HTTP requests.” This matches an unauthenticated pre-authentication injection in a web-facing management endpoint.
Exploitation in the Wild
CISA’s addition to KEV on 16 July 2026 confirms active exploitation. The three-day remediation deadline (due date 19 July 2026) aligns with BOD 26-04 requirements for vulnerabilities assessed as actively exploited with high criticality.
Fortinet products have been actively exploited by threat actors at a high rate in recent years. Documented exploitation of Fortinet management interfaces includes:
- Nation-state actors affiliated with China (including the group tracked as Volt Typhoon and UNC3886) have specifically targeted Fortinet management interfaces in campaigns against critical infrastructure
- CISA and the FBI have previously issued advisories warning that FortiOS and FortiGate vulnerabilities are among the most consistently exploited products for initial access into enterprise and government networks
- Ransomware operators including BlackCat/ALPHV, LockBit, and their successors have used Fortinet VPN and firewall vulnerabilities extensively for initial access
FortiSandbox’s specific position inside security operations networks makes it a high-value target for attackers seeking to understand what the victim organization’s defences can detect, exfiltrate submitted malware samples, or pivot into the security team’s operational infrastructure.
The cloud and PaaS variants (FortiSandbox Cloud, FortiSandbox PaaS) extend the exposure to Fortinet’s own cloud infrastructure. Whether the cloud instances are patched by Fortinet automatically or require customer action should be confirmed with Fortinet support.
Patch and Remediation
Apply the patch specified in Fortinet PSIRT advisory FG-IR-26-141 immediately. Federal agencies face a BOD 26-04 deadline of 19 July 2026.
Fortinet distributes patches through the Fortinet Support portal. The patch applies to on-premises FortiSandbox appliances; contact Fortinet to confirm the update status for FortiSandbox Cloud and PaaS instances.
If patching cannot be completed immediately:
- Restrict network access to the FortiSandbox management interface. The management interface should not be accessible from untrusted networks or the general internet. Enforce firewall rules restricting management interface access to known administrative source IPs.
- Review and disable any remote administration access that is not strictly required.
- Monitor for anomalous outbound connections from the FortiSandbox management host, which would indicate post-exploitation activity.
There is no workaround that removes the OS command injection attack surface without restricting management interface access. The patch is required.
Detection
Network monitoring: Look for HTTP requests to the FortiSandbox management interface from unexpected source IP addresses. Management interfaces should have a well-defined and narrow source IP whitelist; traffic from outside this range warrants investigation.
Request content: HTTP requests to the management interface containing shell metacharacters in parameter values (;, &&, |, backtick sequences, $(...)) indicate exploitation attempts.
Process monitoring: Unexpected shell processes (sh, bash, ash) spawned as child processes of the FortiSandbox web server process indicate successful injection. On FortiSandbox appliances running FortiOS derivatives, examine process trees for unusual execution chains.
Outbound connections: Exploitation often results in a reverse shell or download cradle. Monitor for outbound connections from the FortiSandbox host to external IP addresses on non-standard ports, particularly immediately following inbound HTTP requests to the management interface.
System logs: FortiSandbox maintains system logs under /var/log/. Review for command execution events at anomalous times or by the web server user account. The FortiGate logging format for management commands can help distinguish legitimate administrative activity from injected commands.
For organizations using FortiAnalyzer or FortiSIEM, create detection rules for the above patterns and alert on matches. The combination of an unauthenticated inbound request and an outbound connection shortly after is a high-confidence exploitation indicator.