CVE-2021-20161 in AC2600 TEW-827DRU
Summary
by MITRE • 12/31/2021
Trendnet AC2600 TEW-827DRU version 2.08B01 does not have sufficient protections for the UART functionality. A malicious actor with physical access to the device is able to connect to the UART port via a serial connection. No username or password is required and the user is given a root shell with full control of the device.
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-20161 affects Trendnet AC2600 TEW-827DRU routers running firmware version 2.08B01 and represents a critical security flaw in the device's physical security design. This issue stems from inadequate protection mechanisms surrounding the Universal Asynchronous Receiver-Transmitter (UART) interface, which serves as a communication port typically used for debugging and maintenance purposes during device development. The flaw exposes the router to unauthorized access through a physical connection point that should remain secured and inaccessible to unauthorized parties. The vulnerability falls under the category of insufficient physical security controls and represents a failure in the device's security by design principles.
The technical implementation of this vulnerability allows an attacker with physical access to establish a serial connection to the router's UART port without requiring any authentication credentials. This means that anyone possessing the physical device can directly connect to the router's serial console and obtain immediate root shell access to the system. The lack of authentication requirements for UART access represents a fundamental security failure where the device's built-in debugging interface remains perpetually accessible. This vulnerability is classified as a CWE-254 weakness, specifically related to security features that are not properly implemented or are completely absent. The exposure of a root shell provides complete control over the device, enabling attackers to modify firmware, access network traffic, alter device configurations, and potentially use the compromised router as a pivot point for further attacks within the network.
The operational impact of this vulnerability is severe and far-reaching, as it completely undermines the security posture of the affected routers. An attacker with physical access can exploit this vulnerability to gain unrestricted access to the device's operating system, potentially leading to complete network compromise. The vulnerability can be exploited in various scenarios including insider threats, lost or stolen devices, or unauthorized physical access to network equipment. The affected device becomes a potential entry point for attackers to conduct reconnaissance, establish persistent access, or use the router as a platform for launching attacks against other networked systems. This represents a critical failure in the principle of least privilege and demonstrates how physical security vulnerabilities can lead to complete system compromise. The impact aligns with ATT&CK technique T1059.004 for command and script interpreter, where an attacker gains access to a command shell to execute arbitrary code. The vulnerability also maps to T1018 for remote system discovery, as the compromised device can be used to gather network information and map the surrounding network topology.
Mitigation strategies for this vulnerability require immediate action from device administrators and network security teams. The primary recommendation is to update the firmware to the latest version provided by Trendnet, as this vulnerability has been addressed in subsequent firmware releases. Organizations should implement strict physical access controls to prevent unauthorized individuals from gaining access to network equipment, including securing device locations and implementing proper asset management procedures. Network administrators should also consider implementing device monitoring and anomaly detection to identify potential unauthorized access attempts. The vulnerability highlights the importance of secure device design and the need for manufacturers to implement proper physical security measures, including disabling or securing UART interfaces in production devices. Additionally, organizations should conduct regular security assessments of their network equipment to identify similar vulnerabilities and ensure proper configuration management practices are in place to prevent unauthorized access to critical infrastructure components.