CVE-2025-1977

Executive Summary

CVE-2025-1977 is a privilege escalation vulnerability affecting the Moxa NPort 6100-G2 and 6200-G2 Series serial-to-Ethernet device servers. The flaw resides in the MCC (Moxa CLI Configuration) tool, where an authenticated user with read-only privileges can perform unauthorized configuration changes. This is classified as an Execution with Unnecessary Privileges (CWE-250) issue, allowing a low-privileged attacker to modify device settings that should be restricted, potentially leading to full compromise of the device’s confidentiality, integrity, and availability. The attack can be carried out remotely over the network with low complexity and no user interaction, though it requires specific system conditions to be exploitable. No impact on other systems has been identified, but the device itself is at high risk.

This vulnerability is particularly concerning for industrial environments where Moxa devices are used for critical serial communication, such as in SCADA, manufacturing, and utility networks. The lack of a patch or official advisory from Moxa increases the urgency for defensive measures.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in Moxa’s proprietary software stack. No open-source package dependencies are affected.

CVSS Breakdown & Threat Level

CVSS Score: 9.9 (Critical) – based on the following vector:

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required beyond authentication.
• Privileges Required (PR): Low (L) – Attacker needs only read-only access.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – Only the vulnerable component is affected.
• Confidentiality (C): High (H) – Device configuration and data can be exposed.
• Integrity (I): High (H) – Device settings can be altered.
• Availability (A): High (H) – Device operation can be disrupted.

Threat Level: Critical. The combination of remote exploitability, low privileges required, and high impact makes this a severe risk for industrial control systems.

Deep Dive & Mechanics

The vulnerability stems from improper privilege enforcement in the MCC tool. The MCC is a command-line interface used for configuring Moxa NPort devices. It is designed to enforce role-based access control (RBAC), where read-only users should only be able to view settings, not modify them. However, due to a flaw in the authorization logic, the MCC tool does not properly validate user permissions for certain configuration commands. An authenticated read-only user can send specially crafted commands that bypass the intended restrictions, allowing them to change device parameters such as network settings, serial port configurations, and security policies.

The attack requires:

1. Network access to the device’s management interface (typically port 22/SSH or 23/Telnet, or the MCC-specific port).
2. Valid credentials for a read-only account (e.g., default credentials or compromised accounts).
3. The device must be in a state where the MCC tool is accessible (default configuration).

Once exploited, the attacker can:

• Modify network settings to redirect traffic or cause denial of service.
• Change authentication credentials to lock out legitimate users.
• Alter serial port parameters to disrupt connected equipment.
• Disable security features like encryption or logging.

The root cause is a missing or insufficient privilege check in the MCC command handler. The code likely uses a simple flag to indicate read-only access but fails to enforce it for all commands, allowing write operations to proceed.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, based on the vulnerability description, the vulnerable code likely resembles:

// Vulnerable pseudocode
void handle_command(user_t *user, char *cmd) {
    if (user->role == ROLE_READ_ONLY) {
        // Only check for read commands, but not all write commands
        if (strncmp(cmd, "show", 4) == 0) {
            execute_show(cmd);
        } else {
            // Missing check: write commands are allowed
            execute_write(cmd);
        }
    }
}

A patched version would enforce privilege checks for all commands:

// Patched pseudocode
void handle_command(user_t *user, char *cmd) {
    if (user->role == ROLE_READ_ONLY) {
        if (strncmp(cmd, "show", 4) == 0) {
            execute_show(cmd);
        } else {
            // Deny any non-read command
            printf("Permission denied\n");
        }
    }
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Moxa NPort 6100-G2 or 6200-G2 device with default or known read-only credentials.
• Network access to the device’s management interface (e.g., SSH on port 22 or Telnet on port 23).
• Python 3 and the paramiko library for SSH automation.

Exploitation Steps:

1. Identify the target: Use Shodan or Nmap to find Moxa devices with open management ports.

   nmap -p 22,23 --script banner <target_ip>
   

2. Authenticate with read-only credentials:

   import paramiko
   
   host = "192.168.1.100"
   username = "user"
   password = "user"
   
   client = paramiko.SSHClient()
   client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
   client.connect(host, username=username, password=password)
   

3. Execute unauthorized configuration change:

   # Send a command that should be restricted (e.g., change IP address)
   stdin, stdout, stderr = client.exec_command("set ip 192.168.1.200")
   print(stdout.read().decode())
   

4. Verify the change: The device’s IP address will be altered, confirming exploitation.

Note: No public exploit code is available. The above is a conceptual demonstration.

Blue Team

Detection and Prevention:

• Monitor for unusual configuration changes via syslog or SNMP traps.
• Restrict network access to management interfaces using firewalls or ACLs.
• Enforce strong, unique passwords for all user accounts.
• Disable unused management protocols (e.g., Telnet) and use SSH with key-based authentication.
• Implement network segmentation to isolate Moxa devices from untrusted networks.
• Regularly audit user accounts and remove unnecessary read-only access.

Honeypot Setup:

• Deploy a Moxa NPort emulator (e.g., using honeypy or custom script) to capture exploitation attempts.
• Log all commands sent to the MCC tool for analysis.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Unusual SSH/Telnet sessions from unexpected IP addresses.
  • Configuration change commands (e.g., set ip, set password) in logs.
  • Traffic to/from Moxa devices on non-standard ports.

• Host IOCs:

  • Device configuration changes without authorized user activity.
  • New user accounts or modified passwords.
  • Changes to network settings (IP, gateway, DNS).

• Log IOCs:

  • MCC logs showing commands executed by read-only users.
  • Authentication logs with repeated failed login attempts followed by success.

Detection Engineering

YARA Rule

rule CVE_2025_1977_Moxa_MCC_Privilege_Escalation {
    meta:
        description = "Detects exploitation attempts of CVE-2025-1977 in Moxa NPort devices"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-1977"
    strings:
        $cmd1 = "set ip" ascii wide nocase
        $cmd2 = "set password" ascii wide nocase
        $cmd3 = "set port" ascii wide nocase
        $cmd4 = "set security" ascii wide nocase
        $user = "user" ascii wide nocase
    condition:
        any of ($cmd*) and $user
}

Sigma Rule

title: Moxa NPort Unauthorized Configuration Change
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects attempts to change Moxa NPort device configuration by a read-only user
author: Valters IT
date: 2025-04-10
references:
    - CVE-2025-1977
logsource:
    product: moxa
    service: mcc
detection:
    selection:
        user_role: "read-only"
        command:
            - "set ip*"
            - "set password*"
            - "set port*"
            - "set security*"
    condition: selection
falsepositives:
    - Legitimate admin actions (if user role misconfigured)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"CVE-2025-1977 Moxa NPort Unauthorized Config Change"; flow:to_server,established; content:"set ip"; nocase; content:"user"; nocase; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Restrict network access: Use firewalls to limit management access to trusted IPs only.
2. Change default credentials: Ensure all accounts have strong, unique passwords.
3. Disable read-only accounts: If not needed, remove or disable read-only user accounts.
4. Monitor logs: Enable detailed logging and review for suspicious activity.

Long-term Fix:

• Await an official firmware patch from Moxa. Contact Moxa support for updates.
• If patching is not possible, consider replacing the device with a patched alternative or implementing additional network segmentation.

Workaround:

• Use SSH key-based authentication instead of passwords.
• Implement a jump host for management access to add an extra layer of authentication.

Valters IT