CVE-2021-28842 in TEW-755AP
Summary
by MITRE • 08/11/2021
Null Pointer Deference vulnerability exists 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 os service by sending the POST request to apply_cgi via action do_graph_auth without login_name key.
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Analysis
by VulDB Data Team • 08/15/2021
The CVE-2021-28842 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 running firmware versions 1.11B03. This vulnerability resides within the web interface authentication handling mechanism and specifically impacts the apply_cgi endpoint that processes POST requests for the do_graph_auth action. The flaw occurs when the system attempts to process a request without the required login_name parameter, leading to an unhandled null pointer reference that results in system termination.
The technical implementation of this vulnerability demonstrates a classic null pointer dereference pattern where the application fails to properly validate input parameters before attempting to access memory locations. When a remote attacker sends a crafted POST request to the apply_cgi endpoint with the do_graph_auth action, the system's authentication routine attempts to access the login_name field without first verifying its existence or validity. This condition falls under CWE-476 which specifically addresses null pointer dereference vulnerabilities in software applications. The absence of proper input validation and parameter checking creates a path where the application's execution flow encounters a null reference that cannot be handled gracefully, ultimately leading to a system crash or denial of service condition.
From an operational impact perspective, this vulnerability provides remote attackers with a straightforward method to disrupt service availability on affected TRENDnet devices. The attack requires only a simple HTTP POST request to the vulnerable endpoint, making it accessible to any attacker with network connectivity to the device. The denial of service effect manifests as complete service interruption, rendering the wireless access point unusable until manual reboot or firmware recovery is performed. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under the ATT&CK technique T1499.1 for network denial of service attacks. The vulnerability affects devices that are typically deployed in enterprise and home networking environments, potentially creating widespread service disruption across multiple network segments.
Mitigation strategies for this vulnerability should focus on immediate firmware updates from TRENDnet, as the manufacturer has likely released patches addressing this specific null pointer dereference issue. Network segmentation and access control measures can provide temporary protection by limiting direct internet access to these devices, though this approach does not eliminate the vulnerability itself. Implementing network monitoring to detect unusual POST request patterns targeting the apply_cgi endpoint can help identify potential exploitation attempts. Additionally, organizations should conduct thorough inventory assessments to identify all affected devices and prioritize remediation efforts based on network criticality and exposure levels. The vulnerability highlights the importance of input validation and proper error handling in embedded web applications, particularly those managing network access control and authentication functions.