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  3. W32.Downadup.C

W32.Downadup.C

Risk Level 2: Low

Discovered:
March 6, 2009
Updated:
April 6, 2009 6:30:44 PM
Also Known As:
Mal/Conficker-B [Sophos], Worm:W32/Downadup.DY [F-Secure], Trojan-Downloader.Win32.Kido.a [Kaspersky]
Type:
Trojan, Worm
Infection Length:
88,576 bytes
Systems Affected:
Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows Vista, Windows XP
Once executed, the threat disables the following services:
  • BITS
  • ERSvc
  • WerSvc
  • WinDefend
  • wscsvc
  • wuauserv


It then lowers security settings by deleting the following registry entry to prevent automatic startup of certain software:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"Windows Defender"

It then disables Windows Security Alert notifications by deleting the following registry subkey:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\ShellServiceObjects\{FD6905CE-952F-41F1-9A6F-135D9C6622CC}

It also deletes the following registry subkey to prevent the compromised computer from restarting in safe mode:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SafeBoot

The threat may create the following registry subkeys:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 1]
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 1]

Note: [CLSID 1] is generated from the serial number of the compromised computer and hence will vary.

It may then create the following registry entries:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\[CLSID 2]\"[WORD 1][WORD 2]" = "[BINARY DATA]"

Note:
[CLSID 2] is generated from the serial number of the compromised computer and hence will vary.

[WORD 1] and [WORD 2] are randomly selected from the following list:
  • 64
  • Adobe
  • Agent
  • App
  • Assemblies
  • assembly
  • Audit
  • Backup
  • Boot
  • Boot
  • Browser
  • Build
  • Calendar
  • Center
  • Collaboration
  • Common
  • Component
  • Components
  • Config
  • Control
  • Cursors
  • Debug
  • Defender
  • Definitions
  • Digital
  • Discovery
  • Distribution
  • Documents
  • Downloaded
  • Driver
  • en
  • Event
  • Explorer
  • Files
  • Fonts
  • Framework
  • Gallery
  • Games
  • Globalization
  • Google
  • Hardware
  • Help
  • Helper
  • Image
  • IME
  • inf
  • Installer
  • Installer
  • Intel
  • Inter
  • Internet
  • Java
  • Journal
  • Kernel
  • L2S
  • Live
  • Logon
  • Logs
  • Machine
  • Mail
  • Maker
  • Management
  • Manager
  • Media
  • Microsoft
  • Microsoft
  • Mobile
  • Modem
  • Monitor
  • Movie
  • MS
  • msdownld
  • NET
  • Network
  • New
  • Notify
  • Office
  • Offline
  • Options
  • Packages
  • Pages
  • Patch
  • Performance
  • Photo
  • PLA
  • Player
  • Policy
  • Policy
  • Power
  • Prefetch
  • Profiles
  • Program
  • Publish
  • Reference
  • Registered
  • registration
  • Reports
  • Resources
  • schemas
  • Security
  • Security
  • Server
  • Service
  • Setup
  • Shell
  • Shell
  • Software
  • Speech
  • Storage
  • Support
  • System
  • System
  • Task
  • Tasks
  • Temp
  • Time
  • tmp
  • tracing
  • Trusted
  • twain
  • Universal
  • Update
  • US
  • Video
  • Visual
  • Web
  • Windows
  • winsxs
  • Works
  • Zx

Next, it stops any process containing the following strings in the name:
  • autoruns
  • avenger
  • bd_rem
  • cfremo
  • confick
  • downad
  • dwndp
  • filemon
  • gmer
  • hotfix
  • kb890
  • kb958
  • kido
  • kill
  • klwk
  • mbsa.
  • mrt.
  • mrtstub
  • ms08
  • ms09
  • procexp
  • procmon
  • regmon
  • scct_
  • stinger
  • sysclean
  • tcpview
  • unlocker
  • wireshark


The threat then copies itself to one of the following locations:
  • %ProgramFiles%\Internet Explorer\[RANDOM FILE NAME].dll
  • %ProgramFiles%\Movie Maker\[RANDOM FILE NAME].dll
  • %ProgramFiles%\Windows Media Player\[RANDOM FILE NAME].dll
  • %System%\Windows NT\[RANDOM FILE NAME].dll

It may then create the following file:
Temp%\[CLSID 3]\[NUMBER].tmp

Note:
  • [CLSID 3] is generated from the serial number of the compromised computer and hence will vary.
  • [NUMBER] is a decimal number between 0 and 63 inclusive.

The threat creates the following registry entry, so that it runs every time Windows starts:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\"[RANDOM CHARACTERS]" = "rundll32.exe "[RANDOM DLL FILE NAME]", [RANDOM PARAMETER STRING]"

It creates a service with the following characteristics:
Name: [SERVICE NAME]
Startup Type: Automatic

[SERVICE NAME] is a two word combination taken from the following two lists:
List 1:
  • App
  • Audio
  • DM
  • ER
  • Event
  • Ias
  • Ir
  • Lanman
  • Net
  • Ntms
  • Ras
  • Remote
  • SR
  • Sec
  • Tapi
  • Trk
  • W32
  • Wmdm
  • Wmi
  • help
  • win
  • wsc
  • wuau
  • xml
List 2:
  • access
  • agent
  • auto
  • logon
  • man
  • mgmt
  • mon
  • prov
  • serv
  • Server
  • Service
  • Srv
  • srv
  • svc
  • Svc
  • System
  • Time

It registers the service by creating the following registry entries:
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[RANDOM CHARACTERS]\"ImagePath" = "%System%\svchost.exe -k netsvcs"
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[RANDOM CHARACTERS]\Parameters\"ServiceDll" = "[PATH TO THE THREAT]"


The threat patches the following APIs that are used by Windows to make DNS requests or request URLs:
  • DNS_Query_A
  • DNS_Query_UTF8
  • DNS_Query_W
  • Query_Main
  • sendto


The threat monitors DNS requests to domains containing any of the following strings and blocks access to these domains so that the DNS request appears to have timed out:
  • activescan
  • adware
  • agnitum
  • ahnlab
  • anti-
  • antivir
  • arcabit
  • avast
  • avg.
  • avgate
  • avira
  • avp.
  • av-sc
  • bdtools
  • bit9.
  • bothunter
  • ca.
  • castlecops
  • ccollomb
  • centralcommand
  • cert.
  • clamav
  • comodo
  • computerassociates
  • confick
  • coresecur
  • cpsecure
  • cyber-ta
  • defender
  • downad
  • doxpara
  • drweb
  • dslreports
  • emsisoft
  • enigma
  • esafe
  • eset
  • etrust
  • ewido
  • fortinet
  • f-prot
  • freeav
  • free-av
  • fsecure
  • f-secure
  • gdata
  • gmer.
  • grisoft
  • hackerwatch
  • hacksoft
  • hauri
  • honey
  • ikarus
  • insecure.
  • iv.cs.uni
  • jotti
  • k7computing
  • kaspersky
  • kav.
  • kido
  • llnw.
  • llnwd.
  • malware
  • mcafee
  • microsoft
  • mirage
  • mitre.
  • msdn.
  • msft.
  • msftncsi
  • ms-mvp
  • msmvps
  • mtc.sri
  • nai.
  • ncircle
  • networkassociates
  • nmap.
  • nod32
  • norman
  • norton
  • onecare
  • panda
  • pctools
  • precisesecurity
  • prevx
  • ptsecurity
  • qualys
  • quickheal
  • removal
  • rising
  • rootkit
  • safety.live
  • sans.
  • secunia
  • securecomputing
  • secureworks
  • snort
  • sophos
  • spamhaus
  • spyware
  • staysafe
  • sunbelt
  • symantec
  • technet
  • tenablese
  • threat
  • threatexpert
  • trendmicro
  • trojan
  • vet.
  • virscan
  • virus
  • wilderssecurity
  • windowsupdate


It also connects to the following Web sites to to obtain the current date and time:
  • ask.com
  • baidu.com
  • facebook.com
  • google.com
  • imageshack.us
  • rapidshare.com
  • w3.org
  • yahoo.com


If the date and time is on or after 1st April 2009, it uses the date information to generate a list of domain names. The threat then contacts these domains in an attempt to download additional files on to the compromised computer.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Ka Chun Leung and Sean Kiernan
Summary| Technical Details| Removal

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