In the last few weeks, I’ve seen a significant uptick in systems infected with Chromeloader malware. This malware is a malicious extension for your browser, redirecting it to ad sites and hijacking searches. But with the success of this technique recently, I would not be surprised if others will take notice and switch to using it for other things. 

  

Initial infection 

 The user went to the malicious search results, where the query they searched for presented an ISO file for their search terms. Below is the results of a user that got infected 

https://alizebruisiacult[.]xyz/?cms=Mzg1ODEEDwwMCAYNDQwCAQsCDNDEDgcCDwwPAQAASQ%3D%3D&fn=Stroud%20-%20Advanced%20Engineering%20Mathematics%204e&extt=xpectthatmy.shop%2F%3Ftid%3D952736

 

C:\Users\user\Downloads\Stroud - Advanced Engineering Mathematics 4e.iso 

 

This ISO file contained the following files

files.zip

res.ico

Install.lnk

properties.bat

 

The user double clicked on the Properties.bat file that started the infection process.

Parent Process Name: cmd.exe

Parent Process Command Line: cmd.exe /c ""D:\properties.bat" "

Process Name: tar.exe

Process Command Line arguments: tar -xvf "files.zip" -C "C:\Users\user\AppData\Roaming"

They established persistence with CurrentVersion\Run key.

"opensubtitles-uploader.exe "k2eN"" /f. 

HKEY_CURRENT_USER\S-1-5-21-740110469-27406-3214746-20027\SOFTWARE\Microsoft\Windows\CurrentVersion\

C:\Users\user\AppData\Roaming\opensubtitles-uploader\opensubtitles-uploader.exe.

Connection to some malicious domains from happened from opensubtitles-uploader.exe.

C:\Users\user\AppData\Roaming\opensubtitles-uploader\opensubtitles-uploader.exe.

https://alizebruisiacult[.]xyz

https://raw.githubusercontent[.]com

 

Since the infection is coming from a user mounting and executing files in an ISO, the best way to stop this is to prevent a user from mounting the ISO by double clicking. Users are still able to Burn a CD from within windows if needed. If you have power users that need to open ISOs they can use compression utilities.  

 

Mubix (Rob Fuller) has a great article about how to disable this.(1).  Below, there are two different options to prevent users from double clicking ISO file to mount them.  The GPO method is a little more complete in protections, see the article for more details. We have deployed this in my environment to end users' desktops and have not had any issues to this point nor any new infections via this method.

 

GPO 

Computer config -> Admin Templates -> System -> Device Installation Restrictions ->  

• Allow administrators to override Device Installation Restrictions Policies (enabled) 
• Prevent Installation from devices that match any of these device IDs 

 Add this exact ID    

• SCSI\CdRomMsft____Virtual_DVD-ROM_ 

 

Registry Setting 

• HKEY_CLASSES_ROOT\Windows.IsoFile\shell\mount 
• Value “ProgrammaticAccessOnly” as REG_SZ 
   

(1) https://malicious.link/post/2022/blocking-iso-mounting/ 

If you have done this or something similar, let us know. 

--

Tom Webb

@twsecblog