WORM_DOWNAD.AD

This worm exploits a vulnerability in Server service that, when exploited, allows a remote user to execute arbitrary code on the infected system in order to propagate across networks.

To get a one-glance comprehensive view of the behavior of this Worm, refer to the Threat Diagram shown below.

It propagates by dropping copies of itself in physical and removable drives. It also propagates over the Internet by attempting to send the exploit code to random Internet addresses.

It generates a set of URLs containing 250 random sites per day based on the UTC time standard.

It blocks access to websites that contain certain strings, which are mostly related to antivirus programs.

This worm arrives via removable drives. It may be dropped by other malware.

It modifies registry entries to disable various system services. This action prevents most of the system functions to be used.

It drops copies of itself into all the removable drives connected to an affected system. It drops copies of itself into network drives. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system. It exploits software vulnerabilities to propagate to other computers across a network.

It modifies certain registry entries to hide Hidden files. It prevents users from visiting antivirus-related websites that contain specific strings.

Arrival Details

This worm arrives via removable drives.

It may arrive via network shares.

It may be dropped by other malware.

Installation

This worm drops the following copies of itself into the affected system:

• %Application Data%\{random file name}.dll
• %System%\{random file name}.dll
• %System%\{random number}.tmp
• %Program Files%\Internet Explorer\{random file name}.dll
• %Program Files%\Movie Maker\{random file name}.dll
• %User Temp%\{random file name}.dll

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.. %System% is the Windows system folder, which is usually C:\Windows\System32.. %Program Files% is the default Program Files folder, usually C:\Program Files in Windows 2000, Server 2003, and XP (32-bit), Vista (32-bit), and 7 (32-bit), or C:\Program Files (x86) in Windows XP (64-bit), Vista (64-bit), and 7 (64-bit).. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

• {random characters}
• Global\{random characters based on the computer name}-7

Autostart Technique

This worm registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost\
{random characters}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
ImagePath = "%System Root%\system32\svchost.exe -k"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}\Parameters
ServiceDll = "%System%\{malware file name}"

It adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random characters} = "rundll32.exe {malware path and file name}, Parameter"

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Applets
dl = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Applets
ds = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets
dl = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets
ds = "0"

It modifies the following registry key(s)/entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters
TcpNumConnections = "00FFFFFE"

(Note: The default value data of the said registry entry is user-defined.)

It modifies registry entries to disable the following system services:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\BITS
Start = "4"

(Note: The default value data of the said registry entry is 2.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv
Start = "4"

(Note: The default value data of the said registry entry is 2.)

Propagation

This worm creates the following folders in all removable drives:

• {drive letter}:\Recycler\{SID}

It drops copies of itself into all the removable drives connected to an affected system.

It drops the following copy(ies) of itself in all removable drives:

• {drive letter}:\Recycler\{SID}\{random characters}

It drops copies of itself into network drives.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

It uses the following user name and password to gain access to password-protected shares:

• 99999999
• 9999999
• 999999
• 99999
• 88888888
• 8888888
• 888888
• 88888
• 77777777
• 7777777
• 777777
• 77777
• 66666666
• 6666666
• 666666
• 66666
• 55555555
• 5555555
• 555555
• 55555
• 44444444
• 4444444
• 444444
• 44444
• 33333333
• 3333333
• 333333
• 33333
• 22222222
• 2222222
• 222222
• 22222
• 11111111
• 1111111
• 111111
• 11111
• 00000000
• 0000000
• 00000
• 0987654321
• 987654321
• 87654321
• 7654321
• 654321
• 54321
• zzzzz
• xxxxx
• qqqqq
• aaaaa
• intranet
• controller
• killer
• games
• private
• market
• coffee
• cookie
• forever
• freedom
• student
• account
• academia
• files
• windows
• monitor
• unknown
• anything
• letitbe
• letmein
• domain
• access
• money
• campus
• explorer
• exchange
• customer
• cluster
• nobody
• codeword
• codename
• changeme
• desktop
• security
• secure
• public
• system
• shadow
• office
• supervisor
• superuser
• share
• super
• secret
• server
• computer
• owner
• backup
• database
• lotus
• oracle
• business
• manager
• temporary
• ihavenopass
• nothing
• nopassword
• nopass
• Internet
• internet
• example
• sample
• love123
• boss123
• work123
• home123
• mypc123
• temp123
• test123
• qwe123
• abc123
• pw123
• root123
• pass123
• pass12
• pass1
• admin123
• admin12
• admin1
• password123
• password12
• password1
• default
• foobar
• foofoo
• temptemp
• testtest
• rootroot
• adminadmin
• mypassword
• mypass
• Login
• login
• Password
• password
• passwd
• zxcvbn
• zxcvb
• zxccxz
• zxcxz
• qazwsxedc
• qazwsx
• q1w2e3
• qweasdzxc
• asdfgh
• asdzxc
• asddsa
• asdsa
• qweasd
• qwerty
• qweewq
• qwewq
• nimda
• administrator
• Admin
• admin
• a1b2c3
• 1q2w3e
• 1234qwer
• 1234abcd
• 123asd
• 123qwe
• 123abc
• 123321
• 12321
• 123123
• 1234567890
• 123456789
• 12345678
• 1234567
• 123456
• 12345

It exploits the following software vulnerabilities to propagate to other computers across a network:

• Vulnerability in Microsoft's Server service

Other Details

This worm connects to the following URL(s) to get the affected system's IP address:

• http://www.getmyip.org
• http://www.whatsmyipaddress.com
• http://www.whatismyip.org
• http://checkip.dyndns.org

It connects to the following time servers to determine the current date:

• myspace.com
• msn.com
• ebay.com
• cnn.com
• aol.com
• w3.org
• ask.com
• yahoo.com
• google.com
• baidu.com

It modifies the following registry entries to hide Hidden files:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
CheckedValue = "0"

(Note: The default value data of the said registry entry is 1.)

It does the following:

• Patches TCPIP.SYS in memory in order to modify the limit of maximum TCP half-connection attempts in systems running Windows XP Service Pack 2. It does this by loading TCPIP.SYS in a certain memory location. It then drops %System%\0{random number}.tmp, which is responsible for creating a device object named TcpIp_Perf and linking it to the loaded TCPIP.SYS in memory. It then sends the control code (patch code) to the linked device object.
• Checks if the command line includes the string RUNDLL32.EXE. If it does, this worm assumes it is running as a scheduled task. It then injects itself to the legitimate processes SVCHOST.EXE and EXPLORER.EXE.
• Exports functions used by other malware. It sets the creation time of the file similar to that of the creation time indicated in the legitimate Windows file KERNEL32.DLL, which is also located in the Windows system folder. It does this to prevent early detection as a newly added file on the affected system.
• Checks the operating system version of the affected system. If the worm is running on a Windows 2000 machine, it injects itself to SERVICES.EXE.
• Injects itself to SVCHOST.EXE if the infected system has any of the following operating systems:
  
  • Windows Server 2003
  • Windows Server 2003 R2
  • Windows XP
• Executes the following commands to disable auto-tuning if the system is running under Windows Vista:
  
  • netsh interface tcp set global autotuning=disabled
• Injects itself to the process SVCHOST.EXE to hook NetpwPathCanonicalize and avoid reinfection of an affected system.
• Propagates by taking advantage of a vulnerability discovered in certain Microsoft operating systems that could allow remote code execution if an affected system received a specially crafted RPC request, which also contains a shellcode. More information on the said vulnerability can be found in this Microsoft Web page:
  
  • Microsoft Security Bulletin MS08-067
  Once this specially crafted RPC request reaches its target vulnerable system, the shellcode is decrypted, and then retrieves certain APIs capable of downloading a copy of the worm from the affected system, which is already converted into an HTTP server. The affected system then opens a random TCP port, allowing the vulnerable machine to connect to itself using the following URL:
  
  • http://{IP address of the affected machine}:{random port generated by this worm}/{malware file name composed of random characters}
• Propagating over the Internet by attempting to send the exploit code to random Internet addresses. It first broadcasts the opened random port that serves as an HTTP server so that it is accessible over the Internet. Then, it gets the external IP address of the system to check if it has a direct connection to the Internet. Once a direct connection is made, it launches the exploit code over the Internet by checking the external IP address and the configured IP address in the ethernet or modem driver.
• Drops a copy of itself in the Admin$\System32 folder using a randomly named file using the credentials of the compromised user once it gains access. Upon successful network propagation, a scheduled task is created in the %Windows%\Tasks folder using the NetScheduleJobAdd API to be able to execute its dropped copy. The scheduled time of execution on the created job file is retrieved from GetLocalTime API.
• Generates strings and appends the following extensions to create URLs based on the current date:
  
  • .biz
  • .info
  • .org
  • .net
  • .com.
  • .ws
  • .cn
  • .cc
• Generates a set of URLs containing 250 random sites per day based on the UTC time standard.
• Checks if any of the generated URLs is active and creates a thread to download and execute files. This routine also converts the host name to an IP address to complete the following URL:
  
  • http://{IP address}/search?q=0
  The NetpwPathCanonicalize_hook in NETAPI32.DLL has a function which checks for a generated URL in the RPC traffic. If the URL is active, it will attempt to download the hosted file.
• Creates a named pipe with the following format:
  
  • \.\pipe\System_{random number}
  It then connects to the pipe to read data. The data obtained from the pipe is be passed to the call_create_thread_download function, which is responsible for downloading, validating, and executing the downloaded file.
• Hooks the following APIs to filter a list of antivirus-related sites when being accessed on the Internet:
  
  • DnsQuery_A
  • DnsQuery_UTF8
  • Query_Main

It prevents users from visiting antivirus-related websites that contain the following strings:

• Ccert.
• sans.
• bit9.
• windowsupdate
• wilderssecurity
• threatexpert
• castlecops
• spamhaus
• cpsecure
• arcabit
• emsisoft
• sunbelt
• securecomputing
• rising
• prevx
• pctools
• norman
• k7computing
• ikarus
• hauri
• hacksoft
• gdata
• fortinet
• ewido
• clamav
• comodo
• quickheal
• avira
• avast
• esafe
• ahnlab
• centralcommand
• drweb
• grisoft
• nod32
• f-prot
• jotti
• kaspersky
• f-secure
• computerassociates
• networkassociates
• etrust
• panda
• sophos
• trendmicro
• mcafee
• norton
• symantec
• microsoft
• defender
• rootkit
• malware
• spyware
• virus
• avg
• avp
• eset