CVE-2021-28843 in TEW-755AP
Summary
by MITRE • 08/11/2021
Null Pointer Dereference vulnerability exists in TRENDnet TEW-755AP 1.11B03, TEW-755AP2KAC 1.11B03, TEW-821DAP2KAC 1.11B03, and TEW-825DAP 1.11B03 by sending the POST request to apply_cgi with an unknown action name.
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Analysis
by VulDB Data Team • 08/16/2021
The CVE-2021-28843 vulnerability represents a critical null pointer dereference flaw affecting several TRENDnet wireless access point models including TEW-755AP, TEW-755AP2KAC, TEW-821DAP2KAC, and TEW-825DAP all running firmware versions 1.11B03. This vulnerability resides within the web interface handling mechanism of these network devices, specifically when processing POST requests directed to the apply_cgi endpoint. The flaw manifests when an attacker sends a malicious POST request containing an unknown action name parameter, which triggers improper input validation and subsequent memory management errors within the device's firmware.
The technical implementation of this vulnerability stems from inadequate validation of user-supplied input parameters within the web application layer of the affected TRENDnet devices. When the system receives a POST request to the apply_cgi endpoint with an unrecognized action name, the firmware fails to properly handle the NULL pointer reference that occurs during the processing of this malformed input. This condition violates fundamental security principles and creates a potential denial of service scenario where the device may crash or become unresponsive. The vulnerability aligns with CWE-476 which describes null pointer dereference conditions that can lead to application instability and potential exploitation for more severe attacks.
From an operational standpoint, this vulnerability presents significant risks to network infrastructure security as it allows remote attackers to potentially disrupt network services without requiring authentication. The impact extends beyond simple service disruption since a successful exploitation could provide attackers with opportunities to gain deeper access to the device's internal systems, potentially leading to privilege escalation or further network compromise. The vulnerability affects devices that are commonly deployed in enterprise and small office environments where wireless access points serve as critical network entry points, making them attractive targets for adversaries seeking persistent network access.
The attack surface for this vulnerability is particularly concerning given that it operates at the application layer of the network stack, requiring only basic network connectivity to exploit. Attackers can leverage this flaw by crafting malicious POST requests that target the specific apply_cgi endpoint, potentially causing the affected devices to crash or reboot, thereby creating denial of service conditions that can disrupt legitimate network operations. According to ATT&CK framework, this vulnerability maps to T1499.004 which covers network disruption techniques, and could potentially be leveraged as a stepping stone for more sophisticated attacks. Organizations should consider implementing network segmentation and monitoring to detect anomalous traffic patterns that may indicate exploitation attempts. The recommended mitigations include applying firmware updates from TRENDnet, implementing network access controls to restrict unauthorized access to device management interfaces, and deploying intrusion detection systems to monitor for suspicious POST requests targeting the affected endpoints.