Old Wine in the New Bottle: Mirai Variant Targets Multiple IoT Devices
2023-5-25 21:0:26 Author: unit42.paloaltonetworks.com(查看原文) 阅读量:44 收藏
A pictorial representation of a Mirai variant like IZ1H9. A green robot is surrounded by devices. The Palo Alto Networks and Unit 42 logo are included.

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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:

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

Table of Contents

Campaign Overview
Threat Group Analysis
Malware Analysis
Botnet Client Configuration String Decryption
IZ1H9 Sample Spreading Through HTTP, SSH and Telnet Protocol
Conclusion
Indicators of Compromise
Artifacts
Infrastructure
Additional Resources
Appendix

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 has an inbuilt machine learning-based detection 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

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.

Figure 14 is a screenshot of the Zyxel remote code execution vulnerability. Included is the line that is exploited in the router, /b/zhttpd/.
Figure 14. Zyxel router exploit in the wild.

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