CVE-2025-6893

Executive Summary

CVE-2025-6893 is a privilege escalation vulnerability in Moxa network security appliances and routers. The flaw resides in the /api/v1/setting/data endpoint, where a broken access control mechanism allows a low-privileged authenticated user to call the API without the required permissions. This enables the attacker to access or modify sensitive system configuration data, potentially leading to full system compromise. The vulnerability has a high impact on the affected device itself, though no loss of confidentiality or integrity is reported for 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 due to the potential for privilege escalation and system configuration modification. The attack vector is network-based, requires low privileges, and has high impact on confidentiality, integrity, and availability of the affected device.

Deep Dive & Mechanics

The vulnerability is a classic case of broken access control (CWE-269). The /api/v1/setting/data endpoint is designed to be accessible only by high-privileged users (e.g., administrators). However, due to a flaw in the authorization logic, a low-privileged authenticated user can successfully call this endpoint. This allows the attacker to:

• Read sensitive system configuration data (e.g., network settings, user credentials, firewall rules).
• Modify system configuration data (e.g., change admin passwords, disable security features, alter network routing).
• Escalate privileges to a higher level (e.g., root or admin), potentially gaining full control over the device.

The attack is performed over the network, requiring only a valid low-privileged session. The endpoint likely does not properly validate the user's role or permissions before processing the request.

Vulnerable vs. Patched Code

No specific code or patch is available. The vulnerability is in the access control logic of the /api/v1/setting/data endpoint. A patched version would include proper authorization checks, such as verifying the user's role (e.g., admin) before allowing access to the endpoint.

Exploitation & Lab Setup

Red Team

1. Setup: Deploy a vulnerable Moxa device (e.g., Moxa EDS-405A, Moxa NPort 5150) in a lab environment. Obtain a low-privileged user account (e.g., "user" with password "user").
2. Reconnaissance: Authenticate to the device's web interface and obtain a session token (e.g., cookie or JWT).
3. Exploitation: Send a crafted HTTP request to the /api/v1/setting/data endpoint with the low-privileged session token.

   GET /api/v1/setting/data HTTP/1.1
   Host: <target_ip>
   Cookie: session=<low_priv_session_token>
   

4. Privilege Escalation: If successful, the response will contain sensitive configuration data. Modify the request to POST or PUT to change settings (e.g., change admin password).

   POST /api/v1/setting/data HTTP/1.1
   Host: <target_ip>
   Cookie: session=<low_priv_session_token>
   Content-Type: application/json
   
   {"admin_password": "newpassword123"}
   

5. Post-Exploitation: Use the escalated privileges to access other sensitive endpoints or install backdoors.

Blue Team

1. Detection: Monitor for unusual API calls to /api/v1/setting/data from low-privileged users. Look for anomalies in the request patterns (e.g., high frequency, unusual payloads).
2. Logging: Ensure all API requests are logged with user context (username, role, IP address). Enable detailed logging for the /api/v1/setting/data endpoint.
3. Honeypot: Create a fake endpoint that mimics the vulnerable one to detect scanning or exploitation attempts.
4. Network Segmentation: Isolate Moxa devices on a separate VLAN with strict access controls. Limit exposure to the internet.
5. Patch Management: Monitor Moxa's security advisories for patches. Apply them immediately when available.

Indicators of Compromise (IOCs)

• Network: HTTP requests to /api/v1/setting/data from low-privileged users.
• Logs: Unauthorized access attempts to the endpoint, especially from unexpected IP addresses.
• System: Changes to system configuration files or user accounts without proper authorization.
• File: New or modified files in /etc/ or /var/ directories on the device.

Detection Engineering

YARA Rule

rule CVE_2025_6893_Moxa_API_Access {
    meta:
        description = "Detects exploitation attempts of CVE-2025-6893 in Moxa devices"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-6893"
    strings:
        $api_endpoint = "/api/v1/setting/data"
        $low_priv_user = "user" // Example low-privileged username
    condition:
        $api_endpoint and $low_priv_user
}

Sigma Rule

title: CVE-2025-6893 Moxa API Privilege Escalation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects low-privileged users accessing the /api/v1/setting/data endpoint on Moxa devices
author: Valters IT
date: 2025/04/10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-6893
logsource:
    category: web
    product: moxa
detection:
    selection:
        cs-uri-stem: "/api/v1/setting/data"
        cs-username: "user" // Example low-privileged username
    condition: selection
falsepositives:
    - Legitimate admin access (should be filtered by role)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-6893 Moxa API Privilege Escalation Attempt";
    flow:to_server,established;
    content:"/api/v1/setting/data"; http_uri;
    content:"Cookie: session="; http_header;
    pcre:"/Cookie:\s*session=[a-zA-Z0-9]+/";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

1. Immediate: Restrict access to the /api/v1/setting/data endpoint to only high-privileged users (e.g., administrators). Implement proper role-based access control (RBAC).
2. Short-term: Monitor logs for any unauthorized access attempts. Isolate affected devices from the internet.
3. Long-term: Apply patches from Moxa when available. Consider replacing vulnerable devices with newer models that have proper access controls.
4. Compensating Controls: Use a Web Application Firewall (WAF) to block requests to the vulnerable endpoint from low-privileged users. Implement network segmentation.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert