Network-attached storage (NAS) devices are being targeted by Mukashi, a variant of the Mirai malware, in an effort to launch large-scale distributed denial-of-service (DDoS) attacks, researchers warn.

The attacks, which Palo Alto Networks says have already been spotted in the wild, use brute-force techniques against default credentials in order to access NAS products from Zyxel running firmware 5.21.

Mukashi is attempting to take advantage of a critical vulnerability that would allow cybercriminals to execute code. Researchers said Mukashi, like Mirai, could then be used to aim DDoS attacks at a particular target, or several targets.

Phony Protection Messages

Those who monitor consoles during a Mukashi attack will be greeted with the message, “Protecting your device from further infections.”

In reality, the botnet is stealthily decoding strings such as credentials and command-and-control (C&C) commands before making brute-force attempts to see if default credentials are based on commonly used passwords. Having scanned TCP port 23 on random hosts, Mukashi ensures only a single instance is running on a machine following the initial infection by binding itself to TCP port 23448.

Researchers said Mukashi’s capabilities were equal to that of Mirai, despite some differences in code. Given the latter’s success in causing shutdowns across the internet in 2016, the report said Mukashi should be taken as a serious threat.

Patch, Then Check Passwords

The vulnerability Mukashi targets, also known as CVE-2020-9054, was only discovered in February, which means those behind the attacks will probably be trying to find those who haven’t already dealt with it.

Zyxel has already issued a patch for the flaw, so the first step is ensuring it’s been applied if your organization runs any of those NAS devices or connects to them.

Next, take a second look at your default passwords and make sure they’re not so simple or weak that they could easily be guessed via automation. This is more important than ever as the internet of things (IoT) expands and IoT devices become more essential to organizations in a wide variety of industries.

Mirai was a successful piece of malware — Mukashi is just more proof that cybercriminals will continue to learn from it.