CVE-2025-6949

Executive Summary

CVE-2025-6949 is a critical privilege escalation vulnerability in Moxa network security appliances and routers. The flaw resides in the API authorization mechanism, allowing an authenticated, low-privileged user to create new administrator accounts, including accounts with usernames identical to existing users. This can lead to full administrative control over the affected device and potential account impersonation. The vulnerability impacts the confidentiality, integrity, and availability of the device itself, but does not extend to subsequent systems. No public exploit code or patch is currently available.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the description, the vulnerability would likely score high (8.0-9.0) due to the following factors:

• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (API-based)
• Privileges Required (PR): Low (authenticated user)
• User Interaction (UI): None
• Scope (S): Unchanged (device only)
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High

Threat Level: Critical. Exploitation could lead to full device compromise and lateral movement within the network.

Deep Dive & Mechanics

The vulnerability is an authorization flaw in the API of Moxa devices. The API likely lacks proper checks to prevent low-privileged users from performing administrative actions, such as creating new users. The ability to create accounts with usernames identical to existing users suggests a lack of uniqueness validation, enabling account impersonation.

Attack Flow:

1. Attacker gains initial access with low-privileged credentials (e.g., via default credentials, phishing, or other means).
2. Attacker sends a crafted API request to create a new administrator account.
3. The API processes the request without verifying the user's privileges, creating an admin account.
4. Attacker logs in with the new admin account, gaining full control over the device.

Vulnerable vs. Patched Code

No specific code snippets are available. However, the vulnerability likely exists in the API endpoint responsible for user management. A patched version would include:

• Proper authorization checks (e.g., verifying the requesting user has admin privileges).
• Input validation to prevent duplicate usernames.
• Role-based access control (RBAC) enforcement.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Moxa device with a low-privileged account.
• Network connectivity to the device's API endpoint.

Exploitation Steps:

1. Identify the API endpoint for user creation (e.g., /api/users).
2. Craft a POST request with a low-privileged session token:

   {
     "username": "admin",
     "password": "newpassword",
     "role": "administrator"
   }
   

3. Send the request and verify the new admin account is created.
4. Log in with the new admin credentials.

Example cURL command:

curl -X POST https://target-device/api/users \
  -H "Authorization: Bearer <low-priv-token>" \
  -H "Content-Type: application/json" \
  -d '{"username":"admin","password":"P@ssw0rd!","role":"administrator"}'

Blue Team

Detection:

• Monitor API logs for unauthorized user creation attempts.
• Alert on creation of accounts with duplicate usernames.
• Monitor for privilege escalation events.

Mitigation:

• Restrict API access to trusted IPs.
• Implement strict RBAC.
• Enable logging and alerting for all user management actions.

Indicators of Compromise (IOCs)

• Network: Unusual API requests to user management endpoints from low-privileged users.
• System: New administrator accounts appearing in the user database.
• Logs: API logs showing POST /api/users with low-privileged tokens.
• File: Modified configuration files related to user accounts.

Detection Engineering

YARA Rule

rule CVE_2025_6949_Moxa_PrivEsc {
    meta:
        description = "Detects exploitation attempts for CVE-2025-6949"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $api_endpoint = "/api/users" ascii wide nocase
        $admin_role = "administrator" ascii wide nocase
        $low_priv_token = "Bearer" ascii wide nocase
    condition:
        $api_endpoint and $admin_role and $low_priv_token
}

Sigma Rule

title: Moxa Privilege Escalation via API
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects unauthorized user creation via Moxa API
author: Valters IT
logsource:
    category: web
    product: moxa
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/api/users'
        cs-username: 'low_priv_user'
    condition: selection
falsepositives:
    - Legitimate admin actions
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-6949 Moxa Privilege Escalation Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/api/users"; http_uri;
    content:"administrator"; http_client_body;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Restrict API access to trusted IPs only.
2. Implement strict RBAC and enforce least privilege.
3. Enable detailed logging for all API requests.
4. Monitor for unauthorized user creation.

Long-term Fix:

• Apply vendor patch when available.
• Conduct a security audit of the API authorization logic.
• Implement input validation to prevent duplicate usernames.

Workarounds:

• Disable API access if not required.
• Use network segmentation to isolate Moxa devices.

Valters IT