Researchers spotted a hidden backdoor in Chinese IoT devices from the firm DblTek

Security experts at Trustwave have discovered a hidden backdoor in Internet of Things devices manufactured by the Chinese firm DblTek.

Researchers from Trustwave have discovered a backdoor in IoT devices manufactured by a Chinese vendor that is refusing to fix it.

The backdoored devices are produced by the VoIP firm Dbltek, the researchers speculate the backdoor was introduced for debugging purposes.

The experts discovered that the Telnet interface of the GoIP has an undocumented user, namely “dbladm,” which provides root level shell access on the device. The account is not protected by a password, instead, it is protected by a proprietary challenge-response authentication scheme.

When the attacker tries to Telnet into the device as dbladm, the IoT component tries to connect to UDP port 11000 on 192.168.2.1 on the local network. If the flawed device receives a valid response, it grants access.

“Trustwave recently reported a remotely exploitable issue in the Telnet administrative interface of numerous DblTek branded devices. The issue permits a remote attacker to gain a shell with root privileges on the affected device due to a vendor backdoor in the authentication procedure.” reads the analysis published by Trustwave.

The researchers ethically reported the issue to the IoT vendor, but the manufacturer issued a new firmware with minor changes that leave the access open.

Dbltek then has closed any contact with Trustwave that has continued the analysis of the backdoor and has written the PoC exploits for the backdoors in both the old and new firmware versions.

The flawed firmware is present in almost all Dbltek GSM-to-VoIP devices that are mostly used by small to medium size businesses.

An internet scan for vulnerable devices revealed the existence of hundreds of devices online.

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Pierluigi Paganini

(Security Affairs – Dbltek, VoIP )