CVE-2026-3867

Executive Summary

CVE-2026-3867 is an improper ownership management vulnerability in Moxa Secure Routers. A low-privileged authenticated user can access an exported configuration file containing the hashed administrative password. This allows an attacker to obtain sensitive credentials offline. The vulnerability requires the configuration file to have been exported, limiting exploitation to specific post‑export scenarios. No public exploit code or proof‑of‑concept is currently available.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects Moxa’s proprietary firmware and hardware.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a full vector. Based on the description:

• Attack Vector (AV): Local (requires authenticated access to the router)
• Attack Complexity (AC): Low (exported file is accessible)
• Privileges Required (PR): Low (authenticated user)
• User Interaction (UI): None
• Scope (S): Changed (confidentiality impact to admin credentials)
• Confidentiality (C): High (hashed admin password exposed)
• Integrity (I): None
• Availability (A): None

Estimated CVSS v3.1 Score: 6.5 (Medium) – based on local access and high confidentiality impact.

Deep Dive & Mechanics

The vulnerability stems from improper ownership management of exported configuration files. When a low‑privileged user exports the router’s configuration, the file retains permissions that allow that user to read it. The file contains the hashed password of the administrative account. An attacker with low‑privileged access can:

1. Export the configuration file (if not already exported).
2. Read the file and extract the hashed admin password.
3. Perform offline password cracking (e.g., using hashcat) to recover the plaintext password.

The vulnerability does not affect system integrity or availability, and no subsequent system impact has been identified.

Vulnerable vs. Patched Code

No patched code is available. The vulnerable behavior is in the configuration export functionality where file ownership/permissions are not properly restricted. A hypothetical fix would enforce that exported configuration files are owned by the admin user or have restricted read permissions (e.g., 0600).

Exploitation & Lab Setup

Red Team

1. Prerequisites: Authenticated low‑privileged user on a Moxa Secure Router.
2. Steps:
   • Export the configuration file via the web interface or CLI.
   • Locate the exported file (e.g., /tmp/config.bak or similar).
   • Read the file and extract the hashed admin password.
   • Use a tool like hashcat to crack the hash offline.
3. Example command (after obtaining hash):

   hashcat -m 1000 hash.txt /usr/share/wordlists/rockyou.txt
   

Blue Team

1. Detection: Monitor for unauthorized configuration exports via logs (e.g., config export events).
2. Prevention: Restrict low‑privileged users from exporting configurations. Implement file integrity monitoring on exported files.
3. Response: If an export is detected, immediately rotate the admin password and review user permissions.

Indicators of Compromise (IOCs)

• File: Exported configuration file (e.g., config.bak, router_config.txt)
• Hash: MD5 or SHA256 of the exported file (unknown specific values)
• Log Entry: User [username] exported configuration or similar
• Network: No network‑based IOCs (local file access)

Detection Engineering

YARA Rule

rule Moxa_Config_Export_Admin_Hash {
    meta:
        description = "Detects exported Moxa Secure Router config files containing admin password hash"
        author = "Valters IT"
        date = "2025-04-14"
        reference = "CVE-2026-3867"
    strings:
        $admin_hash = /admin_password_hash\s*=\s*[a-f0-9]{32,}/ nocase
        $config_header = "Moxa Secure Router Configuration" nocase
    condition:
        $admin_hash and $config_header
}

Sigma Rule

title: Moxa Secure Router Configuration Export
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects export of configuration file by low-privileged user
logsource:
    product: moxa
    service: secure_router
detection:
    selection:
        EventID: 1001  # hypothetical export event
        User: "*"
        Action: "export configuration"
    condition: selection
falsepositives:
    - Legitimate admin exports
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"Moxa Config Export Attempt"; flow:to_server; content:"export"; nocase; content:"config"; nocase; within:50; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Restrict low‑privileged users from exporting configuration files. Use RBAC to limit export to admin only.
2. Short‑term: Monitor for unauthorized exports and rotate admin passwords if an export is detected.
3. Long‑term: Apply firmware patch from Moxa when available. Implement file permission controls on exported files.
4. Workaround: Disable configuration export for non‑admin users via CLI or web interface.

Valters IT – Securing your digital frontier.

{/* [Security Hash: 718C326BEF0F54D93670A004] */}