CVE-2018-9149 in Multy X AC3000
Summary
by MITRE
The Zyxel Multy X (AC3000 Tri-Band WiFi System) device doesn't use a suitable mechanism to protect the UART. After an attacker dismantles the device and uses a USB-to-UART cable to connect the device, he can use the 1234 password for the root account to login to the system. Furthermore, an attacker can start the device's TELNET service as a backdoor.
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Analysis
by VulDB Data Team • 01/20/2020
The CVE-2018-9149 vulnerability affects the Zyxel Multy X AC3000 Tri-Band WiFi System, representing a critical security flaw in embedded device design that exposes sensitive system interfaces through inadequate physical security measures. This vulnerability demonstrates a fundamental failure in the device's hardware security architecture, where the UART (Universal Asynchronous Receiver-Transmitter) interface remains accessible without proper protection mechanisms. The flaw allows physical attackers to gain unauthorized access to the device's underlying operating system through straightforward hardware manipulation techniques. The vulnerability specifically targets the device's boot process and system initialization, where default credentials are hardcoded and easily discoverable, creating an immediate path to root-level access.
The technical exploitation of this vulnerability involves physical access to the device, where an attacker must dismantle the hardware enclosure and establish a connection using a standard USB-to-UART cable. This approach aligns with attack patterns described in the MITRE ATT&CK framework under the T1018 technique for Valid Accounts and T1059 for Command and Scripting Interpreter, as it leverages default credentials and system interfaces to achieve unauthorized access. The default password "1234" for the root account represents a severe configuration flaw that violates security best practices and industry standards such as those outlined in NIST SP 800-125B. This hardcoded credential creates an unauthenticated path to full system control, enabling attackers to execute arbitrary commands with the highest privileges available within the device's operating system.
The operational impact of CVE-2018-9149 extends beyond simple unauthorized access to encompass complete system compromise and potential network infiltration. Once an attacker gains root access through the UART interface, they can activate the device's TELNET service, creating a persistent backdoor that allows remote access without requiring additional physical access. This backdoor capability transforms a single device compromise into a potential network-wide threat, as the attacker can use the compromised device as a pivot point to access other networked systems. The vulnerability affects the device's integrity and availability, as the attacker can modify system configurations, install malicious software, or use the device as a staging point for further attacks. This represents a violation of the principle of least privilege and demonstrates how physical security failures can undermine network security controls.
Mitigation strategies for this vulnerability must address both the immediate hardware access issue and the broader security configuration problems. Organizations should implement physical security measures such as tamper-evident seals and secure device enclosures to prevent unauthorized hardware access. The device firmware should be updated to remove hardcoded default credentials and implement proper authentication mechanisms. Network segmentation and monitoring should be deployed to detect anomalous TELNET activity that might indicate a compromised device. Security standards such as those defined in ISO/IEC 27001 and NIST SP 800-125B recommend implementing robust access controls and regular security assessments to prevent similar vulnerabilities. The vulnerability also highlights the importance of secure boot processes and hardware-based security features that can prevent unauthorized access to low-level system interfaces, as recommended in the CWE catalog under CWE-255 for Credentials Management. Regular firmware updates and security audits are essential to address such hardware-level vulnerabilities that may not be apparent through traditional network-based security measures.