CVE-2021-28841 in TEW-755AP
Summary
by MITRE • 08/11/2021
Null Pointer Dereference vulnerability in TRENDnet TEW-755AP 1.11B03, TEW-755AP2KAC 1.11B03, TEW-821DAP2KAC 1.11B03, and TEW-825DAP 1.11B03, which could let a remote malicious user cause a denial of service by sending a POST request to apply_cgi via an action ping_test without a ping_ipaddr key.
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Analysis
by VulDB Data Team • 08/15/2021
This vulnerability represents a critical null pointer dereference flaw affecting multiple TRENDnet wireless access point models including TEW-755AP, TEW-755AP2KAC, TEW-821DAP2KAC, and TEW-825DAP versions 1.11B03. The issue manifests within the web application interface that handles network configuration commands through the apply_cgi script. When a remote attacker sends a specially crafted POST request containing an action parameter set to ping_test without including the required ping_ipaddr key, the application fails to properly validate input parameters before attempting to dereference a null pointer. This fundamental programming error occurs at the application level where the software assumes the presence of a required parameter without proper validation mechanisms.
The technical execution of this vulnerability leverages the web-based management interface of these network devices, making it particularly dangerous as it requires no physical access or authentication credentials to exploit. The attack vector specifically targets the apply_cgi endpoint which processes various network configuration commands including ping operations. When the ping_test action is invoked without the mandatory ping_ipaddr parameter, the application's memory management routines encounter a null pointer reference that results in an immediate application crash or termination. This behavior directly aligns with CWE-476, which defines null pointer dereference as a common software vulnerability where a program attempts to access memory through a null pointer reference.
From an operational impact perspective, this vulnerability creates a reliable denial of service condition that can be exploited by any remote attacker with network access to the affected devices. The affected TRENDnet models are commonly deployed in small office and home environments where network availability is critical for business operations and personal connectivity. The exploitation process is straightforward and requires minimal technical expertise, making it particularly concerning for widespread abuse. The device will likely become unresponsive to management requests and may require manual reboot to restore functionality, potentially disrupting network services for extended periods.
The vulnerability demonstrates poor input validation practices and inadequate error handling within the embedded web application framework of these network devices. According to ATT&CK framework category T1499, this represents a denial of service attack technique that can be executed remotely without authentication, making it a significant threat to network availability. The affected devices operate within environments where network reliability is paramount, and this vulnerability could be exploited by attackers to disrupt business operations or create opportunities for further attacks. Organizations should consider the broader implications of such vulnerabilities in their network infrastructure, particularly when these devices are deployed in critical environments where service availability is essential for operations.
Mitigation strategies should include immediate firmware updates from TRENDnet to address the null pointer dereference vulnerability, network segmentation to limit access to management interfaces, and implementation of intrusion detection systems to monitor for suspicious POST requests targeting the apply_cgi endpoint. Network administrators should also consider disabling unnecessary web management interfaces when not actively required and implementing proper access controls to limit who can submit configuration changes to these devices. The vulnerability highlights the importance of proper input validation and error handling in embedded network devices, as these systems often operate in environments where they are exposed to untrusted network traffic without adequate security boundaries.