CVE-2026-7257

Executive Summary

CVE-2026-7257 is a vulnerability in the Zyxel WRE6505 v2 wireless range extender, specifically in firmware version V1.00(ABDV.3)C0. The flaw involves insecure storage of sensitive information within the device's configuration file. A local attacker with administrator privileges can download and decrypt a backup configuration file, potentially exposing credentials, network keys, and other sensitive data. The product is marked as "UNSUPPORTED WHEN ASSIGNED," meaning it is end-of-life and no patches will be provided. The CVSS score is 4.4 (Medium), with a local attack vector and high privileges required.

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.

CVSS Breakdown & Threat Level

• CVSS Score: 4.4 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N
• Attack Vector: Local (AV:L) – The attacker must have physical or local network access to the device.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: High (PR:H) – Administrator-level access is needed.
• User Interaction: None (UI:N) – No user action is required.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – Sensitive data (e.g., Wi-Fi passwords, admin credentials) can be exposed.
• Integrity Impact: None (I:N) – Data integrity is not compromised.
• Availability Impact: None (A:N) – Service availability is not affected.

Threat Level: Medium. While the impact on confidentiality is high, the requirement for local administrator privileges significantly reduces the attack surface. However, in environments where these devices are still in use, an insider threat or an attacker who has already compromised the device could extract sensitive data.

Deep Dive & Mechanics

The vulnerability resides in the backup configuration file mechanism of the Zyxel WRE6505 v2. The device allows administrators to create a backup of the configuration, which is stored in a file. This file contains sensitive information such as:

• Administrator credentials (username and password)
• Wi-Fi SSID and pre-shared key (PSK)
• Network settings (IP addresses, DHCP configurations)
• Possibly other secrets (e.g., SNMP community strings)

The core issue is that the configuration file is either stored in plaintext or uses a weak, reversible encryption algorithm that can be easily decrypted by an attacker with local access. The attacker, having administrator privileges, can download this file via the web interface or command-line interface (CLI). Once obtained, the file can be decrypted offline using publicly known methods or tools.

The vulnerability is classified under CWE-922 (Insecure Storage of Sensitive Information). The product is end-of-life, meaning no firmware updates will be released to fix this issue.

Vulnerable vs. Patched Code

Since the product is end-of-life and no patch exists, there is no patched code to compare. The vulnerable code is the firmware's backup/restore functionality. A hypothetical fix would involve:

• Encrypting the backup file with a strong, device-specific key (e.g., derived from a hardware security module or a unique device secret).
• Storing the encryption key in a secure, non-extractable location.
• Implementing access controls to prevent unauthorized download of the backup file.

Vulnerable Code (Conceptual):

# Pseudocode for vulnerable backup
def create_backup():
    config = read_config()
    backup_file = base64_encode(config)  # Weak encoding
    save_to_file(backup_file)

Patched Code (Conceptual):

# Pseudocode for patched backup
def create_backup():
    config = read_config()
    key = get_device_secret()
    encrypted_config = aes_encrypt(config, key)
    backup_file = base64_encode(encrypted_config)
    save_to_file(backup_file)

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Local network access to the Zyxel WRE6505 v2.
• Administrator credentials (default or obtained via other means).

Steps:

1. Access the device: Connect to the device's web interface (typically http://192.168.1.1 or similar).
2. Login: Use administrator credentials.
3. Navigate to backup: Go to the "Maintenance" or "Backup & Restore" section.
4. Download backup: Click the "Download" button to save the configuration file (e.g., config.bin).
5. Decrypt the file: Use a tool or script to decrypt the file. For example, if the encryption is a simple XOR or base64, reverse it.

Example Decryption Script (Python):

import base64

def decrypt_backup(file_path):
    with open(file_path, 'rb') as f:
        data = f.read()
    # Assuming base64 encoding
    decoded = base64.b64decode(data)
    # Further decryption if needed (e.g., XOR with a known key)
    # For demonstration, we assume plaintext after base64
    return decoded

backup_data = decrypt_backup('config.bin')
print(backup_data.decode('utf-8', errors='ignore'))

Blue Team (Defender)

Detection:

• Monitor for unauthorized access to the device's web interface.
• Log and alert on backup file downloads.
• Use network monitoring to detect unusual traffic to/from the device.

Mitigation:

• Replace the device with a supported model.
• If replacement is not possible, restrict network access to the device (e.g., VLAN segmentation, firewall rules).
• Change default credentials and use strong, unique passwords.
• Disable remote management if not needed.

Indicators of Compromise (IOCs)

• File Hashes (SHA-256): (Example – actual hash depends on device)
  • config.bin: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
• Network Traffic:
  • HTTP GET requests to /cgi-bin/backup.cgi or similar endpoints.
  • Outbound connections from the device to unknown IPs (if exfiltrated).
• Logs:
  • Successful login from unusual IP addresses.
  • Backup file download events in the device logs.

Detection Engineering

YARA Rule

rule CVE_2026_7257_Zyxel_Backup {
    meta:
        description = "Detects Zyxel WRE6505 backup configuration files"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-7257"
    strings:
        $header = "ZYXEL_CONFIG" ascii wide nocase
        $magic = { 5A 59 58 45 4C 5F 43 4F 4E 46 49 47 } // "ZYXEL_CONFIG" in hex
    condition:
        $header or $magic
}

Sigma Rule

title: Zyxel WRE6505 Backup File Download
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects download of backup configuration file from Zyxel WRE6505
author: Valters IT
date: 2025/04/10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-7257
logsource:
    category: webserver
    product: apache
    service: httpd
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem:
            - '/cgi-bin/backup.cgi'
            - '/backup/config.bin'
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-7257 Zyxel WRE6505 Backup Download"; flow:to_server,established; content:"GET"; http_method; content:"/cgi-bin/backup.cgi"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Replace the device: Since the product is end-of-life, the only complete remediation is to replace the Zyxel WRE6505 v2 with a supported device.
2. Network segmentation: If replacement is not immediately possible, isolate the device on a separate VLAN with strict firewall rules.
3. Change credentials: Ensure all default passwords are changed to strong, unique values.
4. Disable remote management: If not required, disable remote access to the device's web interface.

Long-term Recommendations:

• Implement a device lifecycle management policy to ensure end-of-life devices are replaced.
• Regularly audit network devices for vulnerabilities.
• Use network monitoring tools to detect anomalous behavior.

Valters IT Signature

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters.it.