CVE-2021-28844 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 via a do_graph_auth action without a session_id key.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/16/2021
The CVE-2021-28844 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. This vulnerability resides within the web application interface of these network devices, specifically in the authentication handling mechanism that processes POST requests to the apply_cgi endpoint with the do_graph_auth action. The flaw occurs when the system attempts to dereference a null pointer during the authentication process, creating a potential crash condition that can be exploited by remote attackers.
The technical implementation of this vulnerability stems from insufficient input validation within the web server component of the TRENDnet devices. When an attacker sends a crafted POST request containing the do_graph_auth action but omitting the required session_id parameter, the application fails to properly validate the presence of this critical authentication token. This oversight allows the system to proceed with processing a request that lacks proper session context, leading to a null pointer dereference when the application attempts to access memory locations that have not been properly initialized. The vulnerability manifests as an application crash or unexpected termination, effectively causing a denial of service condition that disrupts legitimate network operations.
From an operational perspective, this vulnerability presents significant security implications for organizations relying on these network devices. The remote exploitability means that attackers can potentially disrupt network services without requiring physical access or authentication credentials. The denial of service impact affects the availability of wireless network services, potentially causing network outages that can affect business operations, employee productivity, and customer access to network resources. The vulnerability affects the core authentication functionality of these devices, which means that legitimate users may be unable to access network services during exploitation attempts, while attackers can leverage the condition to gain unauthorized access or cause persistent service disruption.
The vulnerability aligns with CWE-476, which specifically addresses null pointer dereference conditions in software applications. This classification indicates that the flaw represents a fundamental programming error where the application fails to check for null pointers before dereferencing them, a common weakness in network device firmware implementations. From an attacker's perspective, this vulnerability can be categorized under ATT&CK technique T1499.004, which involves network disruption through denial of service attacks. The impact extends beyond simple service disruption as it can potentially provide a foothold for further exploitation attempts, especially if the device firmware lacks proper error handling and recovery mechanisms.
Mitigation strategies for CVE-2021-28844 should prioritize immediate firmware updates from TRENDnet to address the null pointer dereference condition. Network administrators should implement network segmentation and access controls to limit exposure of these devices to untrusted networks, while also monitoring for unusual traffic patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and error handling in embedded network devices, emphasizing the need for robust security practices in firmware development. Additionally, organizations should consider implementing intrusion detection systems to monitor for crafted POST requests targeting the affected endpoints and establish incident response procedures to address potential exploitation attempts.