Vulnerabilities

Old Wine in the New Bottle: Mirai Variant Targets Multiple IoT Devices

8 min read

Executive Summary

On April 10, Unit 42 researchers observed a Mirai variant called IZ1H9, which used several vulnerabilities to spread itself. The threat actors use the following vulnerabilities to target exposed servers and networking devices running Linux:

CVE-2023-27076: Tenda G103 command injection vulnerability
CVE-2023-26801: LB-Link command injection vulnerability
CVE-2023-26802: DCN DCBI-Netlog-LAB remote code execution vulnerability
Zyxel remote code execution vulnerability

Compromised devices can be fully controlled by attackers and become a part of the botnet. Those devices can be used to conduct further attacks, such as distributed denial-of-service (DDoS) attacks.

Palo Alto Networks Next Generation Firewall customers receive protections through Cloud-Delivered Security Services such as IoT Security, Advanced Threat Prevention, WildFire and Advanced URL Filtering, which can help detect and block the exploit traffic and malware.

Related Unit 42 Topics	Mirai variant, IoT

Campaign Overview

Since November 2021, Unit 42 researchers have observed multiple campaigns using the Mirai IZ1H9 variant. Based on our analysis, we believe that these campaigns were operated by the same threat actor for the following reasons:

The malware shell script downloaders used in both campaigns are almost identical.
The botnet samples use the same XOR decryption key: 0xBAADF00D
The botnet client samples use almost identical functions.
Botnet client samples among those campaigns share the same infrastructure.

On April 10, 2023, Unit 42 researchers observed some abnormal traffic from our threat hunting system. This threat group tried to download and execute a shell script downloader lb.sh from IP 163.123.143[.]126.

If executed, the shell script downloader would first delete logs to hide its tracks. Then the following bot clients would be downloaded and executed, to accommodate different Linux architectures:

hxxp://163.123.143[.]126/bins/dark.x86
hxxp://163.123.143[.]126/bins/dark.mips
hxxp://163.123.143[.]126/bins/dark.mpsl
hxxp://163.123.143[.]126/bins/dark.arm4
hxxp://163.123.143[.]126/bins/dark.arm5
hxxp://163.123.143[.]126/bins/dark.arm6
hxxp://163.123.143[.]126/bins/dark.arm7
hxxp://163.123.143[.]126/bins/dark.ppc
hxxp://163.123.143[.]126/bins/dark.m68k
hxxp://163.123.143[.]126/bins/dark.sh4
hxxp://163.123.143[.]126/bins/dark.86_64

In the last step, the shell script downloader would block network connection from several ports including SSH, telnet and HTTP. It did so by modifying the device’s iptable rules, so that the victim wouldn’t be able to connect and recover the compromised device remotely, as depicted in Figure 1.

Figure one is a screenshot of the modified iptable rules. — Figure 1. Iptable modification.

Threat Group Analysis

Unit 42 researchers conducted analysis on the downloaded botnet client samples and found two URLs hosting more shell script downloaders:

hxxp://2.56.59[.]215/i.sh
hxxp://212.192.241[.]72/lolol.sh

Figure 2 is a diagram illustrating the campaign overview.

Figure 2 is a campaign overview diagram. It starts with the first IP address from April 10, 2023, and leads through the hosts, Mirai samples, the hosts, a shell script, and continues through the different downloaders. — Figure 2. Campaign overview diagram.

The shell script downloader from 2.56.59[.]215 would download botnet clients from hxxp://2.56.59[.]215/bins/. Those botnet client samples would contact a command and control (C2) server at 195.133.40[.]141 where there were URLs in the malware samples that hosted two shell scripts:

hxxp://31.210.20[.]100/lolol[.]sh
hxxp://212.192.241[.]72/lolol[.]sh

The shell script downloader from 212.192.241[.]72 would download botnet clients from hxxp://212.192.241[.]87/bins/, and those botnet client samples would contact the C2 domain dotheneedfull[.]club.

Malware Analysis

Based on behavior and patterns Unit 42 researchers observed during the analysis of the downloaded samples, we believe that they are a variant of the Mirai botnet called IZ1H9.

Discovered in August 2018, IZ1H9 is one of the most active Mirai variants. Just like the original Mirai, the IZ1H9 botnet client first checks the network portion of the infected device’s IP address. The client avoids execution for a list of IP blocks, including government networks, internet providers and large tech companies.

The botnet client makes its presence visible by printing the word “Darknet” to the console. The malware also contains a function that ensures the device is running only one instance of this malware. If a botnet process already exists, the botnet client will terminate the current process and start a new one, as depicted in Figure 3.

Figure 3 is a screenshot demonstrating how the botnet client terminates a current process, and then starts a new one. Included in the code is “instance already exists, overriding current process.” — Figure 3. IZ1H9 ensures there is only a single instance of execution.

The botnet client also contains a list of process names belonging to other Mirai variants and other botnet malware families. The malware checks the running process names on the infected host to terminate them.

The IZ1H9 variant tries to connect to a hard-coded C2 address: 193.47.61[.]75, as shown in Figure 4.

Figure 4 is a screenshot of the malware variant trying to connect to the hardcoded command and control (C2) IP address. — Figure 4. IZ1H9 malware C2 address.

Botnet Client Configuration String Decryption

For botnet client configuration strings, the IZ1H9 variant will first initialize an encrypted string table. It will then retrieve the encrypted strings through an index (as shown in Figures 5 and 6).

Figure 5 is a screenshot of the encrypted string table. Highlighted in red is table_init(). — Figure 5. Initializing the encrypted string table.

Figure 6 is a screenshot of the malware variant retrieving strings. Highlighted within a red box is the code val = table retrieve val (84, 0). This is Mirai retrieving strings by index. — Figure 6. IZ1H9 retrieving strings.

The IZ1H9 variant uses a table key during the string decryption process: 0xBAADF00D. For each encrypted character, the malware performs XOR decryption with the following bytewise operations:

cipher_char ^ 0xBA ^ 0xAD ^ 0xF0 ^ 0x0D = plain_char

According to the logic behind XOR operation, the configuration string key equals to

0xBA ^ 0xAD ^ 0xF0 ^ 0x0D = 0xEA

IZ1H9 Sample Spreading Through HTTP, SSH and Telnet Protocol

For SSH and telnet channels, IZ1H9 inherits the most significant feature from the original Mirai source code: a data section with embedded default login credentials for scanner and brute-force purposes.

The original Mirai and IZ1H9 also both encrypt their login credentials with a 1 byte XOR key. The keys vary in different versions, but this variant uses 0x54, as shown in Figure 7.

Figure 6. IZ1H9 retrieving strings. — Figure 7. IZ1H9 variant credentials XOR decryption.

This IZ1H9 variant initializes the table of nearly 100 pairs of telnet/SSH login credentials in the scanner function. It then spreads through brute forcing network devices’ weak username and password combinations.

For the HTTP channel, IZ1H9 uses four remote code execution vulnerabilities to get access to the vulnerable devices, and it executes the shellcode script downloader shown in Figure 8.

Figure 8 is a screenshot of the exploit scanner function. It shows the Zyxlel RCE, Blink, RCE, Netlog RCE, and the Tense RCE. — Figure 8. Exploit scanner function.

Notice that in the Tenda vulnerability exploit function, the payload downloads tenda.sh from the malware host server but executes netlog.sh, as shown in Figure 9. In this case, the exploit will not work.

Figure 9 is a screenshot of the source code for Mirai. Highlighted in red boxes is tenda.sh, which downloads, and netlog.sh, which executes. — Figure 9: Malware executes wrong downloader.

The malware will initialize all DDoS attack functions before the botnet client establishes a connection with the C2 server. According to the Mirai source code, the malware developer will define the attack method and assign a command code to represent the attack method, as depicted in Figure 10.

Figure 10 is a screenshot of the Mirai source code, with the definitions for all of the attack methods. — Figure 10. Mirai attack method definition.

In this IZ1H9 sample, the threat actor defines a set of attack methods, shown in Table 1.

Command	Attack Method	Description
0	attack_method_tcpsyn	TCP SYN flooding attack
1	attack_method_tcpack	TCP ACK flooding attack
2	attack_method_tcpusyn	TCP URG-SYN flooding attack
3	attack_method_tcpall	TCP DDoS with all options set
4	attack_method_tcpfrag	TCP fragmentation attack
5	attack_method_asyn	TCP SYN-ACK flooding attack
6	attack_method_udpgame	UDP attack targets online gaming servers
7	attack_method_udpplain	UDP flooding with fewer options
8	attack_method_greip	GRE IP flooding attack
9	attack_method_std	STD flooding attack
10	attack_method_udpdns	DNS flooding attack
11	attack_method_udpgeneric	UDP flooding attack
12	attack_app_http	HTTP flooding attack
13	attack_method_dnsamp	DNS amplification attack

Table 1. IZ1H9 attack method.

Conclusion

IoT devices have always been a lucrative target for threat actors, and remote code execution attacks continue to be the most common and most concerning threats affecting IoT devices and linux servers. Exposed vulnerable devices could lead to serious threats.

The vulnerabilities used by this threat are less complex, but this does not decrease their impact, since they could still lead to remote code execution. Once the attacker gains control of a vulnerable device, they can include the newly compromised devices in their botnet. This allows them to conduct further attacks such as DDoS.

To combat this threat, it is highly recommended that patches and updates are applied when possible.

Palo Alto Networks customers receive protection from the vulnerabilities and malware discussed above through the following products and services:

Next Generation Firewall with a Threat Prevention security subscription can help block the attacks with Best Practices via Threat Prevention signatures: 93386, 93718, 93721, 93722.
Advanced Threat Prevention provides inline machine learning that can detect vulnerability exploits in real time.
WildFire can help stop the malware with static signature detections.
Advanced URL Filtering and DNS Security are able to block the C2 domain and malware-hosting URLs.
The Palo Alto Networks IoT Security platform can leverage network traffic information to identify the vendor, model and firmware version of a device, and it can identify specific devices that are vulnerable to particular CVEs.
In addition, IoT Security has inbuilt machine learning-based anomaly detection that can alert the customer if a device exhibits nontypical behavior such as the sudden appearance of traffic from a new source, an unusually high number of connections, or an inexplicable surge of certain attributes typically appearing in IoT application payloads.

Indicators of Compromise

Artifacts

Shell Script Downloader

692a5d099e37cd94923ea2b2014d79e6e613fb061a985069736dd3d55d4330c4
e0b1c324298eeccd54ffc2ff48288ec51fbec44f5f82229537508785a9bda6de
931800d4f84bda7c0368c915dfd27721d63ed0ce6a9bc9f13e1417d4c2fe88f3
64a350a33757f6631dc375632de191967ae59c876b4718a087e299bd54f23844

Mirai Variant Sample

23190d722ba3fe97d859bd9b086ff33a14ae9aecfc8a2c3427623f93de3d3b14
00b151ff78a492b5eae0c8d3c769857f171f8424cf36c3b2505f7d7889109599
212b1af9fd1142d86b61956ac1198623f9017153153cfc20bfeab6a9fd44004a
38406b2effd9fc37ce41ee914fda798de9c9b0e239a0cc94b1464dc2a9984fe9
21185d9b7344edcd8d9c4af174e468c38cb3b061e6bd6bd64a4be9bd3fa27ff5
65a46cd29dad935d067a4289445d2efb2710d44d789bf1bf0efb29f94d20e531
06ef6c76e481d25aa09b3b15959d702be29c22d63bd35524766397e3d36d0d2e
7bfb02c563ae266e81ba94a745ea7017f12010d5491708d748296332f26f04f5
1e29f364f502b313f01f28f1ae85bf27114fae5eede6550809fe5bca58f59174

Infrastructure

Malware C2

193.47.61[.]75
195.133.40[.]141
dotheneedfull[.]club

Malware Host

163.123.143[.]126
2.56.59[.]215
212.192.241[.]72
212.192.241[.]87
31.210.20[.]100

Additional Resources

Mirai Variant V3G4 Targets IoT Devices - Unit 42, Palo Alto Networks
New Mirai Variant Targeting Network Security Devices - Unit 42, Palo Alto Networks
Mirai Variant MooBot Targeting D-Link Devices - Unit 42, Palo Alto Networks
Network Security Trends: August-October 2022 - Unit 42, Palo Alto Networks

Appendix

Campaign-related vulnerability information is listed below:

CVE-2023-27076: Tenda G103 Command Injection Vulnerability

This malicious traffic was first detected as a part of the IZ1H9 campaign on April 10, 2023. The command injection vulnerability is due to the failure to sanitize the value of the language parameter in the cgi-bin/luci interface of Tenda G103.

Figure 11 is a screenshot of the Tenda G103 command injection vulnerability. It shows the cgi-bin. — Figure 11. CVE-2023-27076 exploit in the wild.

CVE-2023-26801: LB-Link Command Injection Vulnerability

We captured this exploit traffic on April 10, 2023. The exploit targets a command injection vulnerability in the LB-Link wireless router’s /goform/set_LimitClinet_cfg component, which does not successfully sanitize the user input in the time1, time2 and mac parameters. This leads to arbitrary command execution.

Figure 12 is a screenshot of the LB-Link command injection vulnerability, including the component that is exploited. — Figure 12. CVE-2023-26801 exploit in the wild.

CVE-2023-26802: DCN DCBI-Netlog-LAB Remote Code Execution Vulnerability

The exploit was detected on April 10, 2023. The exploit works due to the Digital China Network DCBI-Netlog-LAB nsg_masq.cgi component failing to adequately sanitize the user-supplied input data, which leads to remote command execution.

Figure 13 is a screenshot of the DCN DCBI-Netlog-LAB Remote Code execution vulnerability. It shows the nsg_masq.cgi component in the first line of a screenshot. — Figure 13. CVE-2023-26802 exploit in the wild.

Zyxel Remote Code Execution Vulnerability

We observed this exploit traffic on Dec. 16, 2022. The exploit targets the Zyxel router’s /bin/zhttpd/ component. If insufficient input validation is found, the attacker can exploit the vulnerability to launch a remote code execution attack.