Worm:Win32/Conficker.gen!E

For a detailed overview of the Conficker threat family, see the description for Win32/Conficker.

Installation

Worm:Win32/Conficker.gen!E attempts to copy itself to the Windows system folder as a hidden DLL file using a random name. If the attempt fails, it may then attempt to copy itself with the same parameters in the following folders:

• %ProgramFiles%\Internet Explorer
• %ProgramFiles%\Movie Maker

It creates the following registry entry to ensure that it runs each time you start Windows:

In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "<random string>"
With data: "rundll32.exe <system folder>\<malware file name>.dll,<malware parameters>"

It may also load itself as a service that is launched when the netsvcs group is loaded by the system file svchost.exe to ensure that it runs each time you start your computer.

Worm:Win32/Conficker.gen!E may also load itself as a fake service by registering itself under the following key:

HKLM\SYSTEM\CurrentControlSet\Services

It may use a display name that is created by combining two of the following strings:

• Boot
• Center
• Config
• Driver
• Helper
• Image
• Installer
• Manager
• Microsoft
• Monitor
• Network
• Security
• Server
• Shell
• Support
• System
• Task
• Time
• Universal
• Update
• Windows

It may also combine random characters to create the display name.

Spreads via...

Network shares with weak passwords

Worm:Win32/Conficker.gen!E attempts to infect computers within the network.

It first attempts to drop a copy of itself in a target computer's ADMIN share using the credentials of the currently logged-on user.

If this method is unsuccessful, for example, if the current user does not have the necessary rights, then instead the worm obtains a list of user accounts on the target computer. It then attempts to connect to the target computer using each user name and the following weak passwords:

If Win32/Conficker.gen!E successfully accesses the target computer, for example, if a combination of any of the obtained user names and one of the above passwords allows write privileges to the machine, then it copies itself to an accessible admin share as ADMIN$\System32\<random letters>.dll.

Creates remote scheduled job

After compromising a computer remotely, Win32/Conficker.gen!E creates a remote schedule job with the command “rundll32.exe <malware file name>.dll,<malware parameters>" to activate the copy, as shown in the images below:

Mapped and removable drives

Worm:Win32/Conficker.gen!E may drop a copy of itself in all mapped and removable drives using a random file name. The worm creates a folder in the root of these drives named 'RECYCLER' (in Windows XP and previous versions, the folder "RECYCLER" references the "Recycle Bin"). Next, the worm copies itself as the following:

<drive:>\RECYCLER\S-%d-%d-%d-%d%d%d-%d%d%d-%d%d%d-%d\<random letters>.dll

Where %d is a randomly-chosen letter. The worm also drops a corresponding autorun.inf file, which enables the worm copy to execute if the drive is accessed and Autorun is enabled. This autorun.inf file is detected as Worm:Win32/Conficker.B!inf.

The image below shows an infected folder, that could potentially launch the worm when accessing an infected share:

Note that the language in the first option suggests the user could 'open folder to view files' however the option is under 'Install or run program', an indication that opening the folder will actually execute an application. Another hint that the action is to execute the worm is the text 'Publisher not specified'. The highlighted choice under 'General options' in the image above would allow a user to view the share and not execute the worm copy.

MS08-067 HTTP 'call back'

Worm:Win32/Conficker.gen!E spreads to computers that are not yet patched against a vulnerability in the Windows Server service (SVCHOST.EXE). If the vulnerability is successfully exploited, the worm instructs the target computer to download a copy of the worm from the host computer via HTTP protocol using the random port between 1024 and 10000 opened by the worm. The vulnerability is documented in Microsoft Security Bulletin MS08-067.

Payload

Modifies system files

Win32/Conficker modifies the file 'NETAPI32.DLL' in memory to prevent re-infection and further exploitation of the vulnerability addressed by Microsoft Security Bulletin MS08-067.

Modifies system settings

Worm:Win32/Conficker.gen!E changes your computer's settings so that you cannot view hidden files. It does this by modifying the following registry entry:

In subkey: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\Folder\Hidden\SHOWALL
Sets value: "CheckedValue"
With data: "0"

It also modifies your computer's TCP settings to allow a large number of simultaneous connections, where 0x00FFFFFE is hexadecimal and equals 16,777,214 decimal value:

In subkey: HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Sets value: "TcpNumConnections"
With data: "0x00FFFFFE"

The worm drops a .TMP file to aid restarting the TCP/IP service for the modification to take effect. The dropped file is detected as Trojan:WinNT/Conficker.B.

Disables TCP/IP Tuning

Win32/Conficker.gen!E disables Windows Vista TCP/IP auto-tuning in Windows Vista, which may make it easier for the malware to open a channel on your computer, by running the following command:

netsh interface tcp set global auto-tuning=disabled

Stops services

This worm stops several important system services, such as the following:

• Windows Security Center Service (wscsvc) – this notifies you of your security settings (for example, Windows update, Firewall and antivirus settings)
• Windows Update Auto Update Service (wuauserv)
• Background Intelligence Transfer Service (BITS) – used by Windows Update to download updates using idle network bandwidth
• Windows Defender (WinDefend)
• Error Reporting Service (ersvc) – sends error reports to Microsoft to help improve user experience
• Windows Error Reporting Service (wersvc)

Win32/Conficker.gen!E deletes the following registry key for Windows Defender, disabling it from running when the computer starts:

In subkey: HKLM\Software\Microsoft\Windows\CurrentVersion\Run
Deletes value: "Windows Defender"

Blocks access to security websites

Win32/Conficker disables any process from sending network traffic or data that has a module name containing any of the following strings (note that most of these strings are related to antivirus and security software, thus effectively disabling the products from getting signature updates, and possibly preventing users from accessing websites with these strings in the URL):

ahnlab
arcabit
avast
avira
castlecops
centralcommand
clamav
comodo
computerassociates
cpsecure
defender
drweb
emsisoft
esafe
eset
etrust
ewido
f-prot
f-secure
fortinet
gdata
grisoft
hacksoft
hauri
ikarus
jotti
k7computing
kaspersky
malware
mcafee
microsoft
networkassociates
nod32
norman
norton
panda
pctools
prevx
quickheal
rising
rootkit
securecomputing
sophos
spamhaus
spyware
sunbelt
symantec
threatexpert
trendmicro
virus
wilderssecurity
windowsupdate

The worm also hooks DNSAPI.DLL to prevent access to security-related websites.

Resets system restore point

Win32/Conficker.gen!E may reset the computer's system restore point, potentially preventing recovery using System Restore.

Checks for Internet connectivity

Win32/Conficker.gen!E checks if the computer is connects to the Internet by attempting to connect to the following websites:

• aol.com
• cnn.com
• ebay.com
• msn.com
• myspace.com

Downloads arbitrary files

Depending on the date set on your computer, Win32/Conficker.gen!E may build a URL to download files starting on January 1, 2009. The generated URL has a domain name that is based on the current computer date. It uses one of the following top level domains:

• .biz
• .cc
• .cn
• .com
• .info
• .net
• .org
• .ws

The generated domain name is first converted to dot notation, for example, 'aaovt.com' then converted to an IP address such as '192.168.16.0'. This generated IP address is then used for the URL, according to the following pattern:

http://<pseudo-random generated IP>/search?q=%d

Some examples of the constructed URLs are as follows:

It checks your computer's date to see if it's January 1, 2009 or later, and also checks the following websites for the date, presumably for verification; if it determines it's later than January 1, 2009, the malware downloads arbitrary files:

• baidu.com
• google.com
• msn.com
• w3.org
• yahoo.com

Additional information

The name of this threat was derived by selecting fragments of the domain 'trafficconverter.biz', a string found in Worm:Win32/Conficker.A:

(fic)(con)(er) => (con)(fic)(+k)(er) => conficker

Analysis by Tim Liu & Jireh Sanico