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'DoubleDoor' IoT Botnet Uses Two Backdoor Exploits

A newly discovered Internet of Things (IoT) botnet is using two exploits to ensure it can not only bypass authentication on targeted devices, but also render additional protections useless, NewSky Security has discovered. 

Dubbed DoubleDoor, the botnet allows attackers to takeover devices even if the user has authentication enabled and has added a firewall for additional protection. Specifically, the malware abuses CVE-2015–7755, a Juniper Networks SmartScreen OS exploit, and CVE-2016–10401, a Zyxel modem backdoor exploit (also abused by the Hide ‘N Seek botnet).

What NewSky Security discovered was that the botnet first deploys the infamous Juniper Networks exploit, which essentially allows it to get past firewall authentication. The backdoor was initially discovered in the ScreenOS software running on NetScreen firewalls. 

Through this backdoor, the telnet and SSH daemons of Netscreen firewalls become accessible with the hardcoded password <<< %s(un=’%s’) = %u  and any username, regardless of whether a valid one or not. In the initial attack cycle of DoubleDoor, the attack was implemented using the username “netscreen,” NewSky's researchers say. 

Next, the botnet attempts to deploy the backdoor for ZyXEL PK5001Z devices, which is pretty straight forward as well, using a hardcoded su password as zyad5001. This is a privilege escalation exploit, and the botnet’s operators were also observed performing a “password based attack to get a basic privilege account like admin:CenturyL1nk before going for the superuser,” the researchers say. 

The DoubleDoor botnet was also observed performing reconnaissance to ensure the attack was successful and control of the IoT device was achieved. 

“DoubleDoor botnet takes care of this, by using a randomized string in every attack. Lack of any standard string will make sure it is not very easy to classify the recon activity as malicious. The strings have one thing in common though, they are always 8 in length,” the security researchers note. 

The botnet is currently in a nascent phase, with attacks observed only between Jan. 18 and Jan. 27, 2018. Most of the attacks were observed originating from South Korean IPs. The botnet’s attacks are expected to remain low, mainly because they are only effective if the victim runs a specific unpatched version of Juniper ScreenOS firewall and uses unpatched Zyxel modems. 

“Double layer of IoT protection is more common in corporate environments, which don’t rely on built-in IoT authentication and like to protect it with another layer of firewall. Although such corporate devices can be lesser in number, getting control of corporate environment routers can be more valuable for an attacker as it can lead to targeted IoT attacks,” the researchers say. 

Related: Backdoor in Juniper Firewalls Enables Remote Access

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