CVE-2020-14074 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 kick_ban_wifi_mac_allow with a sufficiently long qcawifi.wifi0_vap0.maclist 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. This vulnerability exists within the web interface handling mechanism and specifically affects the apply.cgi script when processing POST requests with the kick_ban_wifi_mac_allow action. The flaw manifests when an authenticated user submits a crafted request containing an excessively long qcawifi.wifi0_vap0.maclist key parameter, which triggers the buffer overflow condition in the ssi binary.
The technical implementation of this vulnerability stems from improper input validation and memory management within the router's firmware. The ssi binary fails to properly bounds-check the incoming qcawifi.wifi0_vap0.maclist parameter before copying it into a fixed-size stack buffer. This classic buffer overflow condition allows an attacker to overwrite adjacent stack memory locations, potentially including return addresses and function pointers. The vulnerability is particularly concerning because it requires only authentication to exploit, meaning that any user with valid credentials can leverage this flaw to execute arbitrary code on the device.
From an operational perspective, this vulnerability presents significant security implications for network administrators and end users. An authenticated attacker can gain complete control over the router's operation, potentially enabling them to modify network settings, redirect traffic, install malware, or use the device as a pivot point for attacking other systems on the network. The attack vector is relatively straightforward since it only requires access to the router's web interface with valid user credentials, making it accessible to both internal and external threat actors who have obtained legitimate login information. This vulnerability directly maps to CWE-121 Stack-based Buffer Overflow and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as it enables arbitrary code execution through the affected binary.
The impact extends beyond immediate device compromise as the affected router could serve as a persistent threat actor foothold within a network infrastructure. Network segmentation may be bypassed if the attacker uses the compromised router to establish command and control channels or to perform man-in-the-middle attacks. The vulnerability also poses risks to the broader network ecosystem since wireless routers often serve as gateways to internal networks and may contain sensitive configuration data or act as network access points for multiple users. Organizations should immediately implement mitigations including firmware updates, network segmentation, and monitoring for unusual network activity patterns that could indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and memory safety practices in embedded systems, particularly those handling user-provided data through web interfaces.