Cryptominer z0Miner Uses Newly Discovered Vulnerability CVE-2021-26084 to Its Advantage Threats Analyst Threats Analyst

Recently, we discovered that the cryptomining trojan z0Miner has been taking advantage of the Atlassian’s Confluence remote code execution (RCE) vulnerability assigned as CVE-2021-26084, which was disclosed by Atlassian in August. Given the increasing popularity of the cryptocurrency market, we expect malware authors behind trojans like z0Miner to constantly update the techniques and entry vectors they use to gain a foothold within a system.

This trojan was initially observed exploiting Oracle’s WebLogic Server RCE, CVE-2020-14882, late last year. Since then, z0Miner has been gaining attention by utilizing different unauthorized RCE vulnerabilities, such as the ElasticSearch RCE bug, aka CVE-2015-1427.

Infection chain

Based on our investigation, we found that the infection chain that leverages the new CVE-2021-26084 flaw (Figure 1) is identical to previous findings on z0Miner, as reported by 360 Netlab and Tencent Security.

Once the Confluence vulnerability is successfully exploited, z0Miner deploys web shells that will download the following malicious files:

• hxxp://213[.]152[.]165[.]29/x[.]bat: detected by Trend Micro as Trojan.BAT.TINYOMED.ZYII
• hxxp://213[.]152[.]165[.]29/uninstall[.]bat: detected by Trend Micro as Trojan.BAT.SVCLAUNCHER.ZYII
• hxxp://213[.]152[.]165[.]29/vmicguestvs[.]dll: detected by Trend Micro as Trojan.Win64.TINYOMED.ZYII
• hxxp://27[.]1[.]1[.]34:8080/docs/s/sys[.]ps1: detected by Trend Micro as Trojan.PS1.Z0MINER.YXAIJ

Figure 1. The infection chain of z0Miner

Evasion mechanisms

The malware has been known to use several persistence and defense evasion mechanisms, one of which is the installation of the file vmicvguestvs.dll that z0Miner disguises as a legitimate integration service called “Hyper-V Guest Integration” (Figure 2).

Figure 2. The creation of the fraudulent “Hyper-V Guest Integration” service

One of the downloaded scripts will also create a scheduled task called .NET Framework NGEN v4.0.30319 32 that poses as a .NET Framework NGEN task, as shown in Figure 3. This scheduled task is designed to download and execute a script from Pastebin every five minutes. However, as of this writing, the contents of the Pastebin URL have already been taken down.

Figure 3. The creation of the scheduled task

The z0Miner trojan will proceed to collect its own mining tools from URLs contained in the file ok.bat, as shown in Figure 4. It also downloads another script named clean.bat to find and delete any cryptocurrency mining payloads from other competitors (Figure 5).

Figure 4. The URLs and file paths of z0Miner’s mining components from the file ok.bat

Figure 5. The clean.bat file that locates and deletes other cryptominers

Security recommendations

Although Atlassian has already released a patch addressing the Confluence vulnerability, users can take further steps to minimize their system’s exposure to threats like z0Miner. Regularly updating their systems and applications with the latest patches plays a critical role in mitigating the risks for end users, ensuring that these security gaps can’t be abused for malicious activities.

To assist with patch management, users can turn to solutions such as Trend Micro™ Deep Security™ and Trend Micro Cloud One™ – Workload Security, which provide virtual patching that protects servers and endpoints from threats that abuse vulnerabilities in critical applications. Trend Micro ™ Deep Discovery™ offers detection, in-depth analysis, and a proactive response to attacks using exploits and other similar threats through specialized engines, custom sandboxing, and seamless correlation across the entire attack life cycle, allowing it to detect threats even without any engine or pattern update.

Similarly, Workload Security defends systems and detects  vulnerabilities and malware with the broadest hybrid cloud security capabilities for a mixed environment of virtual, physical, cloud, and containers. Using techniques like machine learning (ML) and virtual patching, Workload Security also protects new and existing workloads even against unknown threats. It also shields users from exploits that target the Confluence vulnerability via the following rule:

• 1011117 – Atlassian Confluence Server Remote Code Execution Vulnerability (CVE-2021-26084)

Users can also benefit from theTippingPoint® Threat Protection System, which uses comprehensive and contextual awareness analysis for advanced threats that exploit vulnerabilities. Threat intelligence from sources such as Digital Vaccine Labs (DVLabs) and Zero Day Initiative (ZDI) provides maximum threat coverage and virtual patching shields vulnerabilities against exploits. TippingPoint protects customers through the following rule:

• 40260: HTTP: Atlassian Confluence Server and Data Center OGNL Injection Vulnerability     

MITRE ATT&CK Tactics and Techniques

The following are the MITRE ATT&CK tactics and techniques associated with CVE-2021-26084 bundled with z0Miner:

Tactic	Technique
Execution	T1569.002: System Services: Service Execution
Persistence	T1053.005: Scheduled Task T1543.003: Create or Modify System Process: Systems Service
Defense Evasion	T1112: Modify Registry T1489: Service Stop T1562.001: Impair Defenses: Disable or Modify Tools T1036.004: Masquerade Task or Service T1070.004: File Deletion
Discovery	T1033: System Owner/User Discovery T1049: System Network Connections Discovery T1069.001: Permission Groups Discovery: Local Groups T1069.002: Permission Groups Discovery: Domain Groups T1082: System Information Discovery T1087: Account Discovery T1087.001: Account Discovery: Local Account T1087.002: Account Discovery: Domain Account T1124: System Time Discovery
Impact	T1496: Resource Hijacking

Indicators of Compromise (IOCs)

File name	SHA-256 Hash	Detection name
error.jsp	49f3d06419d9578551e584515f44b2ee714e1eef96b94e68ea957f2943deca5a	Possible_SMASPWEBSHELL
504page.jsp empty.jsp		Possible_SMWEBSHELLD
jspath.jsp
jspath.jsp
new3.jsp
new2.jsp	cb339d08c0ad7c4d07b06cae5d7eae032fb1bb1178d80b2a1997a8b8257b5bea	Backdoor.Java.WEBSHELL.SBJKTK
uninstall.bat	a254a26a27e36de4d96b6023f2dc8a82c4c4160a1d72b822f34ffdd5e9a0e0c9	Trojan.BAT.SVCLAUNCHER.SMZTID-A
wxm.exe	0663d70411a20340f184ae3b47138b33ac398c800920e4d976ae609b60522b01	PUA.Win64.Xmrig.KBL
network02.exe	a5604893608cf08b7cbfb92d1cac20868808218b3cc453ca86da0abaeadc0537	Coinminer.Win64.MALXMR.SMA
security.jsp		Backdoor.Java.WEBSHELL.SMC
oxc.vbs		VBS_PSYME.AVH
oxc.vbs		VBS_PSYME.AVH
.solrg	f176d69f18cde008f1998841c343c3e5d4337b495132232507a712902a0aec5e	Trojan.SH.Z0MINER.YXAIJ
1.jpg		Trojan.SH.Z0MINER.YXAIJ
sys.ps1	4a2fbe904e4665939d8517c48fb3d5cb67e9b1482195c41fe31396318118cfc8	Trojan.PS1.Z0MINER.YXAIJ
sys.ps1	e9ba929949c7ea764a298e33af1107ff6feefe884cabf6254ff574efff8a2e40	Trojan.PS1.Z0MINER.YXAIJ
1.jpg		Trojan.BAT.Z0MINER.YXAIJ
clean.bat	7d8b52e263bc548891c1623695bac7fb21dab112e43fffb515447a5cc709ac89	Trojan.BAT.KILLMINE.YXAIJ

URLs

• hxxp://209.141.40.190/oracleservice.exe
• hxxp://209.141.40.190/wxm.exe
• hxxp://27.1.1.34:8080/docs/s/config.json
• hxxp://27.1.1.34:8080/examples/clean.bat
• hxxp://27.1.1.34:8080/docs/s/sys.ps1
• hxxp://222.122.47.27:2143/auth/xmrig.exe
• hxxp://pastebin.com/raw/bcFqDdXx
• hxxp://pastebin.com/raw/g93wWHkR
• hxxp://164.52.212.196:88/eth.jpg
• hxxp://66.42.117.168/BootCore_jsp
• hxxp://164.52.212.196:88/1.jpg
• hxxp://209.141.40.190/xms
• hxxp://172.96.249.219:88/.jpg
• hxxp://172.96.249.219:88/1.jpg 1.bat
• hxxp://172.96.249.219:88/.jpg
• hxxps://zgpay.cc/css/kwork.sh
• hxxps://raw.githubusercontent.com/alreadyhave/thinkabout/main/kwork.sh
• hxxp://209.141.40.190/oracleservice.exe
• hxxp://213.152.165.29/vmicguestvs.dll
• hxxp://213.152.165.29/uninstall.bat
• hxxp://213.152.165.29/x.bat

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