A recently discovered botnet that attacks organizations through Internet of things (IoT) vulnerabilities has added brute-forcing and distributed denial-of-service (DDoS) attack vectors, as well as the ability to exploit new flaws to its growing arsenal, Microsoft security analysts have found. 

The updates to Zerobot, a malware first observed earlier this month by Fortinet researchers, pave the way for more advanced attacks as the threat continues to evolve, according to the Microsoft Security Threat Intelligence Center (MSTIC). As a note, Zerobot is not to be confused with ZeroBot.ai, which is a legitimate chatbot.

MSTIC revealed in a blog post on Dec. 21 that the threat actors have updated Zerobot to version 1.1, which can now target resources through DDoS and make them inaccessible, widening the possibilities for attack and further compromise.

"Successful DDoS attacks may be used by threat actors to extort ransom payments, distract from other malicious activities, or disrupt operations," the researchers wrote in the post. "In almost every attack, the destination port is customizable, and threat actors who purchase the malware can modify the attack according to their target."

Brute-Forcing and Other Tactics

Fortinet researchers already had tracked two previous versions of Zerobot — one that was quite basic and another that was more advanced. The botnet's principal mode of attack originally was to target various IoT devices — including products from D-Link, Huawei, RealTek, TOTOLink, Zyxel, and more — through flaws found in those devices, and then spread to other assets connected on the network that way to propagate the malware and grow the botnet.

Microsoft researchers now have observed the botnet getting more aggressive in its attacks on devices, using a new brute-force vector to compromise weakly secured IoT devices rather than just trying to leverage a known vulnerability, the researchers revealed.

"IoT devices are often internet-exposed, leaving unpatched and improperly secured devices vulnerable to exploitation by threat actors," they wrote in the post. "Zerobot is capable of propagating through brute-force attacks on vulnerable devices with insecure configurations that use default or weak credentials."

The malware attempts to to gain device access by using a combination of eight common usernames and 130 passwords for IoT devices over SSH and telnet on ports 23 and 2323 to spread to devices, the researchers wrote. In their observations alone, the MSTIC team identified numerous SSH and telnet connection attempts on default ports 22 and 23, as well as attempts to open ports and connect to them by port-knocking on ports 80, 8080, 8888, and 2323.

An Expanded Security Vulnerability Exploit List

Zerobot hasn't abandoned its original way to access devices, however, and has even expanded this practice. Prior to its new version, Zerobot already could exploit more than 20 flaws in assorted devices, including routers, webcams, network-attached storage, firewalls, and other products from a host of well-known manufacturers.

The botnet has now added seven new exploits for flaws to its quiver, found in Apache, Roxy-WI, Grandstream, and other platforms, the researchers found.

MSTIC also found new evidence that Zerobot propagates by compromising devices with known vulnerabilities that are not included in the malware binary, such as CVE-2022-30023, a command injection vulnerability in Tenda GPON AC1200 routers, they added.

Zerobot's Post-Compromise Behavior

Researchers also observed more about Zerobot's behavior once it gains device access. For one, it immediately injects a malicious payload — which may be a generic script called "zero.sh" that downloads and attempts to execute the bot, or a script that downloads the Zerobot binary of a specific architecture, they said.

"The bash script that attempts to download different Zerobot binaries tries to identify the architecture by brute-force, attempting to download and execute binaries of various architectures until it succeeds," the researchers wrote.

Once Zerobot achieves persistence, it scans for other devices exposed to the Internet that it can infect, by randomly generating a number between 0 and 255 and scanning all IPs starting with this value.

"Using a function called new_botnet_selfRepo_isHoneypot, the malware tries to identify honeypot IP addresses, which are used by network decoys to attract cyberattacks and collect information on threats and attempts to access resources," the Microsoft researchers wrote. "This function includes 61 IP subnets, preventing scanning of these IPs."

Zerobot 1.1 uses scripts targeting various architectures, including ARM64, MIPS, and x86_64. The researchers also have observed samples of the botnet on Windows and Linux devices, exhibiting different persistence methods based on the OS.

Protecting the Enterprise

Fortinet researchers already had stressed the importance of organizations immediately updating to the latest versions of any devices affected by Zerobot. Given that businesses are losing up to $250 million a year on unwanted botnet attacks, according to a report published last year from Netacea, the danger is real.

To help identify if an organization is vulnerable, Microsoft researchers included an updated list of CVEs that Zerobot can exploit in their post. The MSTIC team also recommended that organizations use security solutions with cross-domain visibility and detection capabilities to detect Zerobot malware variants and malicious behavior related to the threat.

Enterprises should also adopt a comprehensive IoT security solution that allows for visibility and monitoring of all IoT and operational technology (OT) devices, threat detection and response, and integration with SIEM/SOAR and extended detection and response (XDR) platforms, according to Microsoft.

As part of this strategy, they should ensure secure configurations for devices by changing default passwords to strong ones and blocking SSH from external access, as well as use least-privileges access including VPN service for remote access, the researchers said.

Another way to avoid compromise by Zerobot is to harden endpoints with a comprehensive security solution that manages the apps that employees can use and provides application control for unmanaged solutions, they said. This solution also should perform timely cleanup of unused and stale executables sitting on an organization's devices.