Backdoor:W32/Knockex.A

Backdoor:W32/Knockex.A is a backdoor program dropped as part of the payload of a Nullsoft installer (NSIS) program detected as Trojan-Dropper:W32/Knockex.A.

The Nullsoft installer contains the following sub-installers:

• OfferApp-2529.exe - detected either as Trojan-Downloader:W32/Knockex.A or Gen:Variant.Kazy.17250
• OfferApp-2526.exe - detected as Spyware:W32/Inet.B

These installers will themselves install multiple installers, which in turn install malware, adware and spyware programs. Among the installed programs is Backdoor:W32/Knockex.A.

First Installer Dropped - OfferApp-2529.exe

As of this writing, the first installer dropped by Trojan-Dropper:W32/Knockex.A, OfferApp-2529.exe, downloads and executes a backdoor with rootkit capabilities. The backdoor is detected either as Backdoor:W32/Knockex.A or Trojan.Generic.KDV.171682.

Upon execution, the backdoor program drops the following files:

• %systemdir%\cssrss.exe A copy of the downloaded backdoor program.
• %systemdir%\nso12k.sys A rookit driver (detected either as Rootkit:W32/Knockex.A or Trojan.Downloader.Agent.ZBU) that hides the backdoor program

The backdoor program uses the following launch points:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run "WMDM PMSP Service" = %systemdir%\cssrss.exe
• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Driver - service launch point of nso12k.sys

Second Installer Dropped - OfferApp-2526.exe

At the same time the OfferApp-2529.exe file is downloading and executing the backdoor, the second installer file, OfferApp-2526.exe, is executing the following installers:

• myclearsearch-setup.exeInstaller of MyWebSearch/CreativeToolbar AdwareDetected as Adware:W32/MyWebSearch.AG
• inet.exeInstaller of iNetMedia AdwareDetected either as Spyware:W32/Inet.A or Spyware.14597
• brand.exe Web Installer/downloader of BrowserSeek/Zwangi AdwareDetected as Adware:W32/Zwangi.O

When the installers listed are executed, their payloads are installed as separate, independent programs.

Second level of installers from OfferApp-2526.exe

myclearsearch-setup.exe The myclearsearch-setup.exe file drops the following components:

• %programdir%\MyClearSearch\MyClearSearchSvc.exe - detected as Adware:W32/MyWebSearch.AF
• %programdir%\MyClearSearch\ShowMsg.exe - detected as Adware:W32/MyWebSearch.AH
• %programdir%\MyClearSearch\uninstall.exe - uninstaller component.

The myclearsearch-setup.exe file then creates the following service launch point:

• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MyClearSearch Helper Service

And also creates the following registry keys:

• HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\SearchScopes
• HKEY_LOCAL_MACHINE\SOFTWARE\MyClearSearch
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Homepage Protection Service

During installation, the program will also modify the start page for the Internet Explorer web browser:

• HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main "Start Page" = "http://myclearsearch.com/"

inet.exe

When OfferApp-2526.exe is executed, it instructs the inet.exe file installer to download a file from a remote site and install it to the path "C:\Program". During this process, the installer creates the following service launch point:

• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\inetUpServ

It will also create a (functional) uninstallation setting:

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\inet

Brand.exe

Brand.exe is an installer that downloads its own components from a remote site. At the time of writing, the file downloads the following components:

• %programdir%\BrowserSeek\browserseek.dll
• %programdir%\BrowserSeek\browserseek.exe
• %programdir%\BrowserSeek\uninstall.exe

It creates the following service launch point:

• HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\BrowserSeek Service

And also creates the following registry keys:

• HKEY_LOCAL_MACHINE\SOFTWARE\BrowserSeek
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\BrowserSeek