CVE-2020-14079 in TEW-827DRU
Summary
by MITRE
TRENDnet TEW-827DRU devices through 2.06B04 contain a stack-based buffer overflow in the ssi binary. The overflow allows an authenticated user to execute arbitrary code by POSTing to apply.cgi via the action auto_up_fw (or auto_up_lp) with a sufficiently long update_file_name key.
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Analysis
by VulDB Data Team • 06/15/2020
The TRENDnet TEW-827DRU wireless router firmware version 2.06B04 contains a critical stack-based buffer overflow vulnerability in the ssi binary component that presents significant security risks for network administrators and end users. This vulnerability resides within the device's web interface handling mechanism where the firmware processes HTTP POST requests to the apply.cgi endpoint. The specific trigger occurs when an authenticated user submits a POST request containing the action parameter set to either auto_up_fw or auto_up_lp, coupled with a maliciously crafted update_file_name key that exceeds the allocated buffer size. The vulnerability stems from inadequate input validation and bounds checking within the ssi binary's string handling routines, creating an exploitable condition that can be leveraged by attackers who have already gained authentication credentials to the device.
The technical flaw manifests as a classic stack-based buffer overflow where the update_file_name parameter is copied into a fixed-size stack buffer without proper bounds checking. When the input exceeds the buffer capacity, adjacent memory locations including return addresses and control data become overwritten, potentially allowing an attacker to manipulate program execution flow. The ssi binary's insufficient validation allows arbitrary data to be written beyond the intended buffer boundaries, creating a condition where the attacker can inject and execute malicious code with the privileges of the web server process. This type of vulnerability is categorized under CWE-121 Stack-based Buffer Overflow, which represents one of the most common and dangerous classes of software vulnerabilities in embedded systems and network devices. The vulnerability's exploitation requires only authentication access to the device, making it particularly concerning as it can be leveraged by both internal and external attackers who have obtained valid credentials through social engineering, credential theft, or other means.
The operational impact of this vulnerability extends beyond simple code execution, as it fundamentally compromises the device's integrity and can lead to complete system compromise. An attacker who successfully exploits this vulnerability can gain persistent access to the router's network, potentially establishing a backdoor for continued unauthorized access, redirecting traffic through malicious proxies, or using the device as a launching point for attacks against other systems on the local network. The router's role as a network gateway makes it a prime target for attackers seeking to establish persistent presence within a network environment, as it provides access to internal network resources and can serve as a pivot point for lateral movement. Additionally, the vulnerability can be exploited to modify the device's configuration, disable security features, or install malicious firmware that can persist across reboots, making the compromise extremely difficult to detect and remediate. This aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1078 for Valid Accounts, as the exploitation requires legitimate authentication but results in unauthorized persistent access and execution capabilities.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security posture improvements. Device owners should immediately upgrade to firmware versions that contain patches addressing the buffer overflow condition, as TRENDnet has released updated firmware versions that resolve this issue. Network administrators should implement network segmentation and access control measures to limit exposure of such devices to untrusted networks, while also monitoring for unusual network traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of secure coding practices in embedded systems, particularly the necessity of implementing proper input validation, bounds checking, and stack canaries to prevent similar conditions. Organizations should also consider implementing network monitoring solutions that can detect anomalous behavior patterns associated with exploitation attempts, such as unusual POST request patterns or attempts to upload large files to web interfaces. Regular security assessments and vulnerability scanning of network infrastructure should be conducted to identify similar issues in other network devices, as embedded systems often contain multiple such vulnerabilities due to resource constraints and legacy code bases. The vulnerability serves as a reminder of the critical importance of firmware security updates and the need for comprehensive security testing of network infrastructure components.