CVE-2021-28845 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, which could let a remote malicious user cause a denial of service by sending the POST request to apply_cgi via the lang action without a language key.
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Analysis
by VulDB Data Team • 08/15/2021
The CVE-2021-28845 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-based management interface of these devices and stems from improper input validation during the processing of HTTP POST requests. The flaw specifically manifests when the system attempts to handle a POST request directed to the apply_cgi endpoint with the lang action parameter, but without providing a required language key value.
The technical implementation of this vulnerability allows for a remote code execution path that ultimately results in a system crash and subsequent denial of service condition. When an attacker sends a malformed POST request containing the lang action parameter without the corresponding language key, the device's web server process attempts to dereference a null pointer, causing an immediate system termination. This type of vulnerability falls under CWE-476 which specifically addresses null pointer dereference conditions in software implementations. The attack vector is particularly concerning as it requires no authentication credentials and can be executed remotely over the network, making it an attractive target for automated exploitation campaigns.
From an operational perspective, this vulnerability poses significant risks to network availability and business continuity for organizations relying on these wireless access points. The denial of service condition effectively renders the affected devices inoperable, disrupting wireless network access for all connected clients. Network administrators may experience extended downtime while troubleshooting the issue, as the affected devices will require manual intervention including power cycling or firmware reinstallation to restore functionality. The vulnerability also creates opportunities for persistent attack scenarios where adversaries might repeatedly exploit the flaw to maintain network disruption. According to ATT&CK framework, this vulnerability aligns with T1499.004 which covers network disruption techniques, and potentially T1566.001 related to spearphishing with malicious attachments, as attackers might leverage this flaw in broader attack campaigns targeting network infrastructure.
The mitigation strategy for CVE-2021-28845 requires immediate attention from network administrators and security teams. The primary remediation involves applying the latest firmware updates provided by TRENDnet, which should address the input validation flaw in the web server component. Organizations should also implement network segmentation to isolate these vulnerable devices from critical network segments and consider disabling unnecessary web management interfaces. Additionally, monitoring network traffic for suspicious POST requests targeting the apply_cgi endpoint with malformed lang parameters can help detect potential exploitation attempts. Security teams should also review and implement proper access controls, ensuring that only authorized personnel can access the device management interfaces, and establish regular vulnerability assessment procedures to identify similar flaws in other network infrastructure components. The vulnerability demonstrates the importance of robust input validation and proper error handling in embedded web server implementations, particularly in network appliances where availability is paramount to business operations.