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📌 Overview

CVE-2026-39813 is a critical path traversal vulnerability affecting Fortinet FortiSandbox.

The vulnerability arises due to improper validation of user-supplied file paths, allowing attackers to manipulate directory traversal sequences such as ../ to access unauthorized files outside the intended directory structure.

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⚠️ Affected Versions

This issue affects the following versions:

• FortiSandbox 4.4.0 – 4.4.8
• FortiSandbox 5.0.0 – 5.0.5

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🧠 Technical Details

The vulnerability is caused by insufficient sanitization of file path inputs in a backend API component.

Root Causes:

• Lack of input validation on file path parameters
• Improper handling of directory traversal patterns (../)
• Weak access control enforcement in file handling logic

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📸 Demo

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💥 Impact

Successful exploitation may allow an attacker to:

• 📂 Access sensitive system files
• 🔐 Retrieve confidential data
• ⚙️ Escalate privileges
• 🧨 Compromise system integrity

CVSS Score: 9.8 (Critical)

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🛠️ Mitigation

Recommended Actions:

• Upgrade FortiSandbox to the latest patched version
• Restrict access to administrative APIs
• Implement strict input validation and sanitization
• Apply allowlist-based file path controls
• Monitor logs for suspicious traversal attempts

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🔒 Security Best Practices

To prevent similar issues:

• Never trust user input for file paths
• Use canonical path validation
• Apply least privilege principles
• Keep systems regularly updated
• Enable intrusion detection and monitoring

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📎 References

• Fortinet Security Advisory
• CVE Database: CVE-2026-39813
• National Vulnerability Database (NVD)

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⚡ Disclaimer

This document is intended for educational and defensive security research purposes only.
No exploit code or malicious instructions are included or supported.

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