CVE-2021-20156

Vulnerability

In the Trendnet AC2600 TEW-827DRU router running firmware version 2.08B01, the firmware update mechanism does not perform any cryptographic signature validation. This improper access control configuration [1] allows an attacker to install firmware that may be malicious, as there is no verification that the update originates from a known and trusted source [1]. The vulnerability covers both manual firmware installation and the automated "check for updates" feature in the admin interface [1].

Exploitation

An attacker must be in a network position capable of masquerading as the legitimate firmware update server, for example through a man-in-the-middle (MITM) attack on the connection used by the device to check for updates. No authentication or user interaction beyond the standard update process is required. When the device performs an automated update check, the attacker can serve a crafted malicious firmware image, which the device will accept without verification [1].

Impact

Successful exploitation allows the attacker to install arbitrary firmware on the device, achieving full compromise of the router's operating system and all its functions. This can lead to complete loss of confidentiality, integrity, and availability (CIA), as the attacker can execute arbitrary code, modify network traffic, exfiltrate data, or render the device inoperable [1].

Mitigation

No fixed firmware version has been released or disclosed in the available references [1]. Users should monitor Trendnet's official support site for updates. As a workaround, ensure that the device is not accessible from the WAN interface and that its update process is performed over a trusted network. The device has reached a status where no further security patches are known to be available [1].