CVE-2025-53949: Fortinet FortiSandbox RCE Vulnerability

CVE-2025-53949 Overview

CVE-2025-53949 is an OS command injection vulnerability [CWE-78] affecting Fortinet FortiSandbox. The flaw stems from improper neutralization of special elements in operating system commands. An authenticated attacker can send crafted HTTP requests to execute unauthorized code on the underlying system.

The vulnerability affects FortiSandbox 5.0.0 through 5.0.2, 4.4.0 through 4.4.7, and all versions of the 4.2 and 4.0 branches. Fortinet published the advisory on December 9, 2025 and tracks the issue as FG-IR-25-479.

Critical Impact

Authenticated attackers can execute arbitrary OS commands on FortiSandbox appliances, compromising confidentiality, integrity, and availability of malware analysis infrastructure.

Affected Products

• Fortinet FortiSandbox 5.0.0 through 5.0.2
• Fortinet FortiSandbox 4.4.0 through 4.4.7
• Fortinet FortiSandbox 4.2 (all versions) and 4.0 (all versions)

Discovery Timeline

• 2025-12-09 - CVE-2025-53949 published to NVD
• 2025-12-09 - Fortinet publishes security advisory FG-IR-25-479
• 2025-12-09 - Last updated in NVD database

Technical Details for CVE-2025-53949

Vulnerability Analysis

The vulnerability resides in the HTTP request handling logic of FortiSandbox. Input passed through specific HTTP parameters reaches an OS command execution context without sufficient sanitization of shell metacharacters. An authenticated user can inject command separators or substitution sequences that the operating system shell interprets and executes.

FortiSandbox is a network-attached malware analysis appliance. Code execution on this platform can expose analyzed sample artifacts, integration credentials for FortiGate and FortiMail, and detonation results used to inform protective controls across the broader Fortinet deployment.

The attack vector is network-based with low complexity. The attacker requires valid authentication but no user interaction, and successful exploitation grants high impact across confidentiality, integrity, and availability.

Root Cause

The root cause is improper neutralization of special elements used in an OS command, classified under [CWE-78]. The application constructs a shell command incorporating attacker-controlled input from HTTP request fields without escaping or using a safe execution API such as parameterized process invocation.

Attack Vector

Exploitation requires an authenticated session against the FortiSandbox management interface. The attacker submits a crafted HTTP request containing shell metacharacters such as backticks, semicolons, or $() substitution sequences within a vulnerable parameter. The injected payload executes with the privileges of the web service process on the appliance.

No verified proof-of-concept code is publicly available at the time of publication. Refer to the Fortinet Security Advisory FG-IR-25-479 for vendor technical detail.

Detection Methods for CVE-2025-53949

Indicators of Compromise

• Unexpected child processes spawned by the FortiSandbox web service, particularly shell interpreters such as sh, bash, or /bin/busybox
• HTTP request logs containing shell metacharacters (;, |, &, `, $()) within parameter values
• Outbound network connections from the FortiSandbox appliance to unexpected destinations
• New or modified files in writable directories not associated with sample analysis

Detection Strategies

• Inspect FortiSandbox HTTP access logs for authenticated requests containing encoded command separators or substitution syntax
• Correlate authentication events with anomalous administrative actions occurring shortly after login
• Monitor for deviations from baseline process trees on the appliance management plane
• Hunt for lateral movement attempts originating from the FortiSandbox IP toward FortiGate, FortiManager, or AD infrastructure

Monitoring Recommendations

• Forward FortiSandbox syslog and HTTP audit logs to a centralized SIEM for correlation
• Alert on administrative HTTP endpoints accessed from unusual source IPs or accounts
• Establish a behavioral baseline for outbound traffic from sandbox appliances and flag deviations
• Track failed and successful authentication attempts against the FortiSandbox management interface

How to Mitigate CVE-2025-53949

Immediate Actions Required

• Upgrade FortiSandbox to a fixed release as specified in Fortinet Security Advisory FG-IR-25-479
• Restrict management interface access to trusted administrative networks using firewall policies
• Rotate credentials for all accounts with access to the FortiSandbox management plane
• Audit recent authenticated sessions and HTTP requests for evidence of exploitation

Patch Information

Fortinet has published remediation guidance in advisory FG-IR-25-479. Administrators should consult the advisory for fixed version numbers corresponding to each affected branch and apply upgrades according to vendor procedures. Refer to the Fortinet PSIRT advisory for the authoritative upgrade matrix.

Workarounds

• Limit administrative access to FortiSandbox to a dedicated management VLAN reachable only by authorized operators
• Enforce multi-factor authentication on all FortiSandbox administrative accounts to raise the bar for credential abuse
• Apply principle of least privilege by removing unnecessary administrative accounts and reviewing role assignments
• Monitor and alert on all administrative HTTP requests until patches are deployed

# Example: restrict FortiSandbox management access via FortiGate policy
config firewall policy
  edit 0
    set name "restrict-fortisandbox-mgmt"
    set srcintf "mgmt"
    set dstintf "sandbox-net"
    set srcaddr "admin-jumphosts"
    set dstaddr "fortisandbox-mgmt"
    set service "HTTPS" "SSH"
    set action accept
    set logtraffic all
  next
end