A targeted campaign delivering the ZLoader banking trojan is spreading via Google AdWords, and is using a mechanism to disable all Windows Defender modules on victim machines. According to SentinelLabs, hackers are lowering rates of detection by using an infection chain for the campaign that also includes the use of a signed dropper with a backdoored version of the Windows utility wextract.exe to embed the ZLoader payload itself.
ZLoader is not new, but tis exploit addition is. It has been noted as typical a banking trojan which implements web injection to steal cookies, passwords and any sensitive information. It attacks users of financial institutions all over the world and has also been used to deliver ransomware families like Egregor and Ryuk. It also provides backdoor capabilities and acts as a generic loader to deliver other forms of malware.
ZLoader Infection Chain Starts with Google AdWords To target victims, the malware is spread from a fake Google advertisement (published through Google AdWords) for various software; the lures include Discord, Java plugins, Microsoft’s TeamViewer and Zoom.
For example, when someone Googles “Team Viewer download” a fake advert appears in AdWords (advert has already been taken down, but it does indicate that diligence is need to make sure the URL and company is correct for any downloads), an advertisement shown by Google on the search engine, that redirects the clicker to a fake TeamViewer site under the attacker’s control. From there, the user can be tricked into downloading a fake installer in a signed MSI format. Current versions have a signed timestamp of Aug. 23, but this is likely to change as it is exposed.
SentinelLabs advise that “It appears that the cybercriminals managed to obtain a valid certificate issued by Flyintellect Inc., a Software company in Brampton, Canada”; “[t]he company was registered on 29 June 2021, suggesting that the threat actor possibly registered the company for the purpose of obtaining those certificates”.
Bypassing and disabling Windows Defender check The downloaded and legitimately signed .MSI file is of course not an installer for legitimate software, but is rather the first-stage dropper for the malware. It runs an installation wizard that creates the following directory: C:Program Files (x86)Sun Technology NetworkOracle Java SE, and saves a .BAT file appropriately called “setup.bat” and then executes the built-in Windows cmd.exe function to execute that file. Users often see the flash of a cmd prompt as Microsoft often use it during windows updates, so do not suspect anything. The executed .BAT then begins stage two and downloads a second-stage dropper that initiates the third stage of infection by executing a script called “updatescript.bat”.
The third stage dropper contains logic impairment to shutdown defenses of the machine by disabling all the Windows Defender modules through the PowerShell cmdlet Set-MpPreference. It then adds exclusions, such as regsvr32, *.exe, *.dll, with the cmdlet Add-MpPreference to hide all the components of the malware from Windows Defender.
Once completed, stage four is executed with the download of the .EXE from URL (hxxxURL://pornofilmspremium.com/tim.exe) which is saved and executed through the Windows explorer.exe function.
At this point the attacker is able to break the parent/child correlation often used by endpoint detection and response (EDRs). As the The tim.exe binary is actually a backdoored version of the legitimate Windows utility wextract.exe but with the hackers additional code, hackers can now legitimately execute the malicious batch file with the name “tim.bat” that runs a short script to download the final ZLoader DLL payload, with the name tim.dll. This final payload is executed using the legitimate Windows function regsvr32, which allows the attackers to proxy the execution of the DLL through a signed binary by Microsoft and execute the functions to exploit the machine.
Tim.bat also downloads another script, called “nsudo.bat” to perform multiple operations to elevate privileges on the system and impair defenses as follows:
- It checks if the current context of execution is privileged by verifying the access to the SYSTEM hive.
- It implements an auto elevation VBScript that aims to run an elevated process in order to make system changes.
The snippet of the script in charge of the UACPrompt feature is as follows:
:UACPrompt echo Set UAC = CreateObject^("Shell.Application"^) > "%temp%getadmin.vbs" set params = %*:"=" echo UAC.ShellExecute "cmd.exe", "/c %~s0 %params%", "", "runas", 1 >> "%temp%getadmin.vbs" "%temp%getadmin.vbs" del "%temp%getadmin.vbs" exit /B
- Once the elevation occurs, the script is run with elevated privileges to perform the steps of disabling Windows Defender on a persistent basis by making sure that the “WinDefend” service is deleted at the next boot through the utility NSudo, and completely disables Microsoft’s User Account Control (UAC) security.
The nsudo.bat script also completely disables UAC by setting the following registry key to 0 (zero):
- After executing these functions it forces a system restart, so that the changes take place and users are unaware.
The purpose of the exploits is to tie the machine into the botnet for bitcoin mining and other operations including DDos attack's as the following extract of DDos URL's show:
@https://commerzbank.de @https://.de//entry* @https://.de/banking-/portal?* @https://.de/banking-/portal;* @https://.de/portal/portal @https://.de/privatkunden/ @https://.deabmelden* @https://.de/de/home @https://.de/en/home @https://.de/fi/home @https://banking.sparda.de @https://banking.sparda- @https://banking.sparda.de/wps/loggedout.jsp @https://meine.deutsche-bank.de/trxm/db* @https://banking.berliner-bank.de/trxm* @https://meine.norisbank.de/trxm/noris @https://targobank.de @https://banking4.anz.com/IBAU/BANKAWAY @https://banking.westpac.com.au/ @https://www1.my.commbank.com.au/netbank/Portfolio/Home/ @https://ibanking.stgeorge.com.au/ibank/ @https://ibanking.banksa.com.au/ibank/ @https://ibanking.bankofmelbourne.com.au/ibank/ @https://online.macquarie.com.au/ @https://ob.cua.com.au/ib/ @https://banking.bendigobank.com.au/banking @https://internetbanking.suncorpbank.com.au/ @https://www.ing.com.au/securebanking/ @https://ib.nab.com.au/ @https://online.beyondbank.com.au/ @https://ib.greater.com.au @www.independentreserve.com @www.coinspot.com.au
Google advise that if you come across any advert that redirects you should report it via the following:
- At all time use an adblocker software to aid in disruption of this exploit.
I realize Google will not be happy about this, but until the system is fixed from such exploits, it is better to be safe. Google should consider formal verification, not just address location verification for advertisers. Perhaps verifying and monitoring advertising URLS may also be something they should consider?
- Do not click on ads. Manually go to the advertisers company rather than clicking on the advert.
Again Google will be unhappy as this is their revenue source. But until its fixed, and confirmed safe, AdWords is currently just another tool in the hackers toolbox
- Verify the domain name and download link before clicking on a URL. Don't assume it is correct.