CVE-2021-20156 in AC2600 TEW-827DRU
Summary
by MITRE • 12/31/2021
Trendnet AC2600 TEW-827DRU version 2.08B01 contains an improper access control configuration that could allow for a malicious firmware update. It is possible to manually install firmware that may be malicious in nature as there does not appear to be any signature validation done to determine if it is from a known and trusted source. This includes firmware updates that are done via the automated "check for updates" in the admin interface. If an attacker is able to masquerade as the update server, the device will not verify that the firmware updates downloaded are legitimate.
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-20156 affects Trendnet AC2600 TEW-827DRU routers running firmware version 2.08B01 and represents a critical improper access control configuration that undermines the device's security posture. This flaw stems from the absence of cryptographic signature validation mechanisms during firmware update processes, creating a pathway for malicious actors to compromise network infrastructure through unauthorized firmware installations. The vulnerability exists within the router's update mechanism that fails to authenticate the legitimacy of firmware sources, particularly when updates are downloaded through the automated "check for updates" functionality in the administrative interface. The lack of verification processes means that any firmware image, regardless of its source or integrity, can be installed on the device without proper authorization or validation.
This security weakness directly maps to CWE-284, which describes improper access control vulnerabilities where systems fail to properly enforce access restrictions and validation mechanisms. The vulnerability creates a significant attack surface that aligns with multiple tactics outlined in the MITRE ATT&CK framework, particularly focusing on T1547.001 for system service modification and T1078.004 for valid accounts. Attackers exploiting this vulnerability can leverage man-in-the-middle techniques to intercept update communications and replace legitimate firmware with malicious payloads, potentially gaining persistent access to the network infrastructure. The threat landscape surrounding such vulnerabilities is particularly concerning as routers serve as critical network gateways, making them attractive targets for adversaries seeking long-term network access and control.
The operational impact of CVE-2021-20156 extends beyond simple unauthorized firmware installation, as it enables sophisticated attack vectors including persistent backdoor installation, network traffic interception, and lateral movement within compromised networks. Once a malicious firmware update is installed, attackers can modify the router's behavior to redirect traffic, monitor network communications, or establish covert channels for data exfiltration. The vulnerability affects both manual and automated update processes, meaning that even users who do not actively seek to install modified firmware may unknowingly accept malicious updates. Organizations with multiple affected devices face significant risk of coordinated attacks that could compromise entire network perimeters through a single vulnerable router. The lack of signature validation creates a fundamental trust model failure where the device cannot distinguish between legitimate and malicious firmware sources, undermining the security of the entire network infrastructure.
Mitigation strategies for CVE-2021-20156 should prioritize immediate firmware updates from official Trendnet sources when available, though users must verify that the update process itself is not compromised through network monitoring or manual verification. Network administrators should implement additional protective measures including network segmentation to isolate affected devices, monitoring for unauthorized firmware installations, and implementing network-based intrusion detection systems to identify suspicious update traffic. The vulnerability highlights the importance of secure update mechanisms and proper cryptographic validation, which should be addressed through firmware development practices that include digital signature verification and secure boot processes. Organizations should also consider implementing network access controls and firewall rules that restrict update server communications to prevent unauthorized firmware sources from reaching affected devices, while maintaining detailed logs of all update activities for forensic analysis and security monitoring purposes.