Trojan:Win32/Vundo.AX is a variant of Win32/Vundo, a multiple-component family of programs that deliver 'out of context' pop-up advertisements. They may also download and execute arbitrary files.
Vundo is often distributed as a DLL file and installed on an affected machine as a Browser Helper Object (BHO) without a user's consent. This family uses advanced defensive and stealth techniques to escape detection and to hinder removal.
Installation
Members of the Vundo family may compromise an affected system in a number of different ways. They use diverse methods of installation that often includes multiple components.
Vundo may use a dropper/downloader component that may be detected as one of the following:
TrojanDropper:Win32/Vundo.A
TrojanDropper:Win32/Vundo.B
TrojanDownloader:Win32/Vundo
(For additional detail on Vundo's downloading functions, please see the Payload section further below.)
If a downloader component is used, it downloads the DLL component, saving it with a filename that may be either randomly generated, or created using any of the following two strings:
abr
av
anti
ac
acc
ad
ap
as
bin
bas
bak
cab
cat
cmd
com
cr
drv
db
disk
dll
dns
dos
doc
dvd
eula
exp
fax
font
ftp
hard
iis
img
inet
info
ip
java
kb
key
lib
log
main
ms
mc
mfc
mp3
msvc
net
nut
odbc
ole
pc
ps
play
ras
reg
run
sys
srv
svr
svc
tapi
tcp
task
un
url
util
vb
vga
vss
xml
wave
web
w
win
wms
For example, 'sysnet.dll'. A unique Class ID registry key may be created to load the newly created DLL. Registry key Class ID values vary among variants. For example:
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{35F7813A-AF74-4474-B1DC-7EE6FB6C43C6}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{39D2FC9B-041C-470E-AE72-F8C001247626}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{44240BB5-BD7D-4D49-A1AA-8AB0F3D3CB44}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{52B1DFC7-AAFC-4362-B103-868B0683C697}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{6DD0BC06-4719-4BA3-BEBC-FBAE6A448152}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{7BF451AC-2010-4804-B256-DB2F0A8D9EB6}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{827DC836-DD9F-4A68-A602-5812EB50A834}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{8DBF02DA-4360-4A7E-BEA1-347B87816327}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{AF7FCAFB-9FDB-4F5E-BAC6-68BDEE61D6C6}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{FC148228-87E1-4D00-AC06-58DCAA52A4D1}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{B8B55274-0F9A-41E5-9067-A3539BD9E860}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{CBE0D59D-F985-4AC6-8826- FEE957065D42}
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID\{5AEFF965-B1A9-4675-966A-26C2E812AD51}
In some variants, several data files are also created in the same location, using the same name but with the following file extensions (as opposed to '.dll'):
For example, 'sysnet.ini', 'sysnet.tmp'.
In some variants, the trojan may utilize an executable component that may be copied to the any of the following locations:
%windir%\addins
%windir%\AppPatch
%windir%\assembly
%windir%\Config
%windir%\Cursors
%windir%\Driver Cache
%windir%\Drivers
%windir%\Fonts
%windir%\Help
%windir%\inf
%windir%\java
%windir%\Microsoft.NET
%windir%\msagent
%windir%\Registration
%windir%\repair
%windir%\security
%windir%\ServicePackFiles
%windir%\Speech
%windir%\system
%windir%\system32
%windir%\Tasks
%windir%\Web
%windir%\Windows Update Setup Files
%windir%\Microsoft\
Vundo may make several registry modifications in order to load itself when Windows is started, for example:
Adds value: <trojan filename>
With data: <trojan path and filename.dll>
To subkeys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce
It may also make further modifications to load the program during events such as user logon and logoff, for example:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify\<name of module>
This trojan family may also modify the following registry entry to load itself at startup: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellExecuteHooks
(Note: this usage is disabled by default in Windows Vista with policy control).
In order to protect itself from being deleted by anti-virus software, the trojan may monitor and possibly modify the following registry entry to rename its file when the system restarts:
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\PendingFileRenameOperations
Vundo may create a mutex 'SysUpdIsRunningMutex' to monitor thread creation and ensure that the program remains running.
Vundo may also inject its code into the following processes if they are found to be running on the affected machine:
Ad-aware.exe
Wrsssdk.exe
Hijackthis.exe
Payload
Vundo is designed with delivering 'out of context' advertisements in mind, however, it may also take a number of additional actions on an affected machine in order to satisfy this purpose, including modifying an affected machine's Internet and security settings and sending information from the affected system to a remote server.
Displays Advertisements/Downloads and Executes Arbitrary Files
Vundo has been observed to contact a number of different IP addresses and particular domains in order to access the advertising material that it displays. It may also download and execute arbitrary files, including updates or additional components. Vundo has been observed to connect to the following IP addresses in the wild for this purpose (for example):
69.31.80.180
72.247.31.80
69.31.80.179
65.243.103.52
207.226.179.18
65.54.225.100
62.4.84.56
Terminates Security Services
Vundo may terminate services associated with the following security-related applications:
AD-AWARE.EXE
GCASSERVALERT.EXE
Spyware Doctor
Modifies Browser Behavior
Vundo may redirect URLs entered by the user to URLs of the program's choice.
Also, when particular URLs are visited by an affected user, Vundo may disable the display of pop-ups. Presumably this is an anti-competitive measure, as the list of targeted URLs contains a number of popular search engines and domain names associated with ad-servers, for example:
yahoo.com
search.ebay.com
web.ask.com
banners.pennyweb.com
ads2.revenue.net
www2.yesadvertising.com
images.trafficmp.com
z1.adserver.com
ads1.revenue.net
ads.doubleclick.net
ads.180solutions.com
Vundo also disables pop-ups if a targeted URL contains "mil" or "gov" in the domain.
Modifies System Security Settings
Virtuemonde makes the following registry modification in an attempt to bypass firewalls:
Sets value: "ProxyBypass"
With data: "1"
To subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ZoneMap\
Sends Information to Remote Server
Virtuemonde may gather and send the following information from the affected machine to a remote server:
Additional Information
Vundo has been observed in the wild being bundled with rogue anti-spyware products, for example, it has been observed being bundled with 'Evidence Eraser Pro'.
Virtuemonde has also been observed using encryption techniques in order to obfuscate its communications with remote sites.
This family may create the following registry entries in which to store data:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\aldd
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SysUpd
Analysis by Jaime Wong
