NOTE: The term “Zerobot” in this article refers to a specific malware variant. It is not in any way associated with zerobot.ai, an organization that offers a verbal chatbot service.
In November, FortiGuard Labs observed a unique botnet written in the Go language being distributed through IoT vulnerabilities. This botnet, known as Zerobot, contains several modules, including self-replication, attacks for different protocols, and self-propagation. It also communicates with its command-and-control server using the WebSocket protocol. Based on some IPS signatures trigger count (shown in Figure 1), this campaign started its distribution of the current version sometime after mid-November.
Affected platforms: Linux
Impacted parties: Any organization
Impact: Remote attackers gain control of the vulnerable systems
Severity level: Critical
This article details how this malware leverages vulnerabilities and examines its behavior once inside an infected device.
Infection
Zerobot targets several vulnerabilities to gain access to a device and then downloads a script for further propagation. The complete script is shown in Figures 2 and 3. Note that the downloading URL was changed from http[:]//zero[.]sudolite[.]ml/bins to http[:]//176[.]65.137[.]5/bins. This Zerobot variant targets the following architectures: i386, amd64, arm, arm64, mips, mips64, mips64le, mipsle, ppc64, ppc64le, riscv64, and s390x. It is saved using the filename “zero,” which is how the campaign name was derived.
Zerobot has two versions. The first one used before November 24 only contains basic functions. The current version has added a “selfRepo” module to reproduce itself and infect more endpoints with different protocols or vulnerabilities. The function list from the older version can be seen in Figure 4. However, the following technical analysis is based on the newer version.
Technical Analysis – Initialization
Zerobot first checks its connection to 1.1.1.1, the DNS resolver server from Cloudflare.
It then copies itself onto the targeted device based on the victim’s OS type. For Windows, it copies itself to the “Startup” folder with the filename “FireWall.exe”. Linux has three file paths: “%HOME% “, “/etc/init/”, and “/lib/systemd/system/”.
It then sets up an “AntiKill” module to prevent users from disrupting the Zerobot program. This module monitors a particular hex value and uses “signal.Notify” to intercept any signal sent to terminate or kill the process.
Technical Analysis – Commands
After initialization, Zerobot starts a connection to its C2 server, ws[:]//176[.]65[.]137[.]5/handle, using the WebSocket protocal.
The data sent from the victim is shown in Figure 9. Based on the WebSocket protocol, we can unmask it to get the JSON with the victim’s information:
{“Platform”:”linux”,”GCC”:”386″,”CPU”:1,”Payload”:”Direct”,”Version”:1}
After the communication channel setup, the client waits for a command from the server, including “ping”, “attack”, “stop”, “update”, “kill”, “disable_scan”, “enable_scan‘, and “command”. Details about the exploit in “enable_scan” is in next section.
Technical Analysis – Exploit
Zerobot includes 21 exploits. The list is shown in Figure 12, and the affected products in Figure 13 are listed below. In addition to some IoT vulnerabilities, it includes Spring4Shell, phpAdmin, F5 Big, etc., to increase its success rate.
The two exploits named “ZERO_xxxxx” at the top of Figure 12 were collected from the website “0day.today” (Figure 14). This site shares numerous exploits for “educational” purposes. The numbers “36290” and “32960” were assigned from this website.
The payload data injected in the exploit is the same as the script file shown in Figure 3.
Conclusion
Zerobot is a new botnet written in the Go programming language. It communicates via the WebSocket protocol. It first appeared on November 18 and is designed to target a variety of vulnerabilities. Within a very short time, it was updated with string obfuscation, a copy file module, and a propagation exploit module that make it harder to detect and gives it a higher capability to infect more devices. Users should be aware of this new threat, patch any affected systems listed in Figure 13 running on their network, and actively apply patches as they become available.
Fortinet Protections
This malware is detected and blocked by FortiGuard Antivirus as:
ELF/Zerobot.A!tr
The FortiGuard AntiVirus service is supported by FortiGate, FortiMail, FortiClient, and FortiEDR, and the Fortinet AntiVirus engine is a part of each of those solutions. Customers running current AntiVirus updates are protected.
Fortinet has released IPS signatures to proactively protect our customers from the threats contained in the exploit list.
The FortiGuard Web Filtering Service blocks the C2 server.
FortiGuard IP Reputation and Anti-Botnet Security Service proactively block these attacks by aggregating malicious source IP data from the Fortinet distributed network of threat sensors, CERTs, MITRE, cooperative competitors, and other global sources that collaborate to provide up-to-date threat intelligence about hostile sources.
IOCs
C2:
176[.]65[.]137[.]5
Files:
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