CVE-2021-20159 in AC2600 TEW-827DRU
Summary
by MITRE • 12/31/2021
Trendnet AC2600 TEW-827DRU version 2.08B01 is vulnerable to command injection. The system log functionality of the firmware allows for command injection as root by supplying a malformed parameter.
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-20159 affects Trendnet AC2600 TEW-827DRU routers running firmware version 2.08B01 and represents a critical command injection flaw that allows attackers to execute arbitrary commands with root privileges. This vulnerability specifically targets the system log functionality within the router's firmware, creating an attack vector where malicious input can be processed without proper sanitization. The flaw stems from inadequate input validation mechanisms that fail to properly filter or escape user-supplied parameters before they are passed to underlying system commands. The vulnerability has been categorized under CWE-77 as "Command Injection," which is a well-documented weakness in software applications where untrusted data is incorporated into system command calls without proper validation or sanitization. This type of vulnerability is particularly dangerous in network infrastructure devices as it provides attackers with elevated privileges typically reserved for system administrators or firmware developers.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass complete system compromise and potential network infiltration. Attackers can leverage this command injection flaw to execute arbitrary commands as the root user, effectively granting them full administrative control over the affected router. This level of access enables adversaries to modify router configurations, install malicious firmware, redirect network traffic, establish persistent backdoors, or use the compromised device as a pivot point for attacking other systems within the local network. The vulnerability affects the router's logging functionality, which is typically used for monitoring system activities and debugging purposes, but becomes a critical attack surface when input parameters are not properly validated. The exploitation requires minimal privileges and can be achieved through web interface interactions, making it particularly dangerous for unpatched devices that are widely deployed in residential and small office environments.
From a threat modeling perspective, this vulnerability aligns with several ATT&CK techniques including T1059.001 for Command and Scripting Interpreter and T1566.001 for Phishing. The attack surface is particularly concerning because it allows for remote code execution without requiring authentication, and the root-level privileges provide complete control over network traffic routing and device configuration. The vulnerability exists due to insufficient input validation and sanitization practices in the firmware codebase, where user-controllable parameters are directly incorporated into system commands without proper escaping or filtering mechanisms. Network security professionals should note that this vulnerability affects not only the specific Trendnet model but potentially other devices in the same product line that utilize similar firmware components. The impact is amplified by the widespread deployment of these routers in residential networks where users may not regularly update firmware or implement additional security controls. Organizations and individuals should immediately assess their network infrastructure for affected devices and implement mitigations including firmware updates, network segmentation, and monitoring for suspicious log entries that might indicate exploitation attempts.
The remediation approach for this vulnerability requires immediate firmware updates from Trendnet to address the command injection flaw in the system logging component. Security administrators should also implement network monitoring to detect potential exploitation attempts through unusual log entries or command execution patterns. Additional mitigations include disabling unnecessary services, implementing strict access controls, and deploying network intrusion detection systems that can identify malicious input patterns targeting the vulnerable logging functionality. The vulnerability demonstrates the critical importance of input validation in embedded systems and firmware development, particularly in network infrastructure devices where the attack surface can have significant implications for overall network security. Regular firmware updates and security assessments of network equipment are essential practices to prevent exploitation of similar vulnerabilities in other network devices.