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  3. W32.Downadup.B

W32.Downadup.B

Risk Level 2: Low

Discovered:
December 30, 2008
Updated:
May 14, 2012 2:18:55 PM
Also Known As:
Worm:W32/Downadup.AL [F-Secure], Win32/Conficker.B [Computer Associates], W32/Confick-D [Sophos], WORM_DOWNAD.AD [Trend], Net-Worm.Win32.Kido.ih [Kaspersky], Conficker.D [Panda Software]
Type:
Worm
Systems Affected:
Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows Server 2008, Windows Vista, Windows XP
CVE References:
CVE-2008-4250
Once executed, the worm checks for the presence of the following registry entries and if not present will create them:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\"dl" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Applets\"dl" = "0"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\"ds" = "0"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Applets\"ds" = "0"


It then copies itself as one or more of the following files:
  • %ProgramFiles%\Internet Explorer\[RANDOM FILE NAME].dll
  • %ProgramFiles%\Movie Maker\[RANDOM FILE NAME].dll
  • %System%\[RANDOM FILE NAME].dll
  • %Temp%\[RANDOM FILE NAME].dll
  • C:\Documents and Settings\All Users\Application Data \[RANDOM FILE NAME].dll


It creates a new service with the following characteristics:
Service Name: [PATH TO WORM]
Display Name: [WORM GENERATED SERVICE NAME]
Startup Type: Automatic

Next, it registers as a service by creating the following registry entries:
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[WORM GENERATED SERVICE NAME]\Parameters\"ServiceDll" = "[PATH TO WORM]"
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[WORM GENERATED SERVICE NAME]\"ImagePath" = %SystemRoot%\system32\svchost.exe -k netsvcs
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[WORM GENERATED SERVICE NAME]\"Type" = "4"
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[WORM GENERATED SERVICE NAME]\"Start" = "4"
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\[WORM GENERATED SERVICE NAME]\"ErrorControl" = "4"


Note: [WORM GENERATED SERVICE NAME] represents a two word combination taken from a list of the following words:
  • Boot
  • Center
  • Config
  • Driver
  • Helper
  • Image
  • Installer
  • Manager
  • Microsoft
  • Monitor
  • Network
  • Security
  • Server
  • Shell
  • Support
  • System
  • Task
  • Time
  • Universal
  • Update
  • Windows


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

Next, the worm deletes any System Restore points created by the user.

The worm then runs a command that speeds up network access on the compromised computer by disabling the Windows Vista TCP/IP auto-tuning to spread more rapidly.

The worm also modifies the following registry entry so that the worm spreads more rapidly across a network:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\"TcpNumConnections" = "00FFFFFE"

Next the worm stops both of the following Windows services:
  • Background Intelligent Transfer Service (BITS)
  • Windows Automatic Update Service (wuauserv)


The worm then modifies the following file in order to disable the half-open connections limit introduced with Windows XP SP2:
%System%\drivers\tcpip.sys

It also attempts to hide itself on the system by modifying the following registry value:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\explorer\Advanced\Folder\Hidden\SHOWALL\"CheckedValue" = "0"

Next, the worm enumerates available ADMIN$ network shares. It then enumerates the users for those shares and attempts to establish a connection as an existing user, with one of the following passwords:
  • 000
  • 0000
  • 00000
  • 0000000
  • 00000000
  • 0987654321
  • 111
  • 1111
  • 11111
  • 111111
  • 1111111
  • 11111111
  • 123
  • 123123
  • 12321
  • 123321
  • 1234
  • 12345
  • 123456
  • 1234567
  • 12345678
  • 123456789
  • 1234567890
  • 1234abcd
  • 1234qwer
  • 123abc
  • 123asd
  • 123qwe
  • 1q2w3e
  • 222
  • 2222
  • 22222
  • 222222
  • 2222222
  • 22222222
  • 321
  • 333
  • 3333
  • 33333
  • 333333
  • 3333333
  • 33333333
  • 4321
  • 444
  • 4444
  • 44444
  • 444444
  • 4444444
  • 44444444
  • 54321
  • 555
  • 5555
  • 55555
  • 555555
  • 5555555
  • 55555555
  • 654321
  • 666
  • 6666
  • 66666
  • 666666
  • 6666666
  • 66666666
  • 7654321
  • 777
  • 7777
  • 77777
  • 777777
  • 7777777
  • 77777777
  • 87654321
  • 888
  • 8888
  • 88888
  • 888888
  • 8888888
  • 88888888
  • 987654321
  • 999
  • 9999
  • 99999
  • 999999
  • 9999999
  • 99999999
  • a1b2c3
  • aaa
  • aaaa
  • aaaaa
  • abc123
  • academia
  • access
  • account
  • Admin
  • admin
  • admin1
  • admin12
  • admin123
  • adminadmin
  • administrator
  • anything
  • asddsa
  • asdfgh
  • asdsa
  • asdzxc
  • backup
  • boss123
  • business
  • campus
  • changeme
  • cluster
  • codename
  • codeword
  • coffee
  • computer
  • controller
  • cookie
  • customer
  • database
  • default
  • desktop
  • domain
  • example
  • exchange
  • explorer
  • file
  • files
  • foo
  • foobar
  • foofoo
  • forever
  • freedom
  • fuck
  • games
  • home
  • home123
  • ihavenopass
  • Internet
  • internet
  • intranet
  • job
  • killer
  • letitbe
  • letmein
  • login
  • Login
  • lotus
  • love123
  • manager
  • market
  • money
  • monitor
  • mypass
  • mypassword
  • mypc123
  • nimda
  • nobody
  • nopass
  • nopassword
  • nothing
  • office
  • oracle
  • owner
  • pass
  • pass1
  • pass12
  • pass123
  • passwd
  • password
  • Password
  • password1
  • password12
  • password123
  • private
  • public
  • pw123
  • q1w2e3
  • qazwsx
  • qazwsxedc
  • qqq
  • qqqq
  • qqqqq
  • qwe123
  • qweasd
  • qweasdzxc
  • qweewq
  • qwerty
  • qwewq
  • root
  • root123
  • rootroot
  • sample
  • secret
  • secure
  • security
  • server
  • shadow
  • share
  • sql
  • student
  • super
  • superuser
  • supervisor
  • system
  • temp
  • temp123
  • temporary
  • temptemp
  • test
  • test123
  • testtest
  • unknown
  • web
  • windows
  • work
  • work123
  • xxx
  • xxxx
  • xxxxx
  • zxccxz
  • zxcvb
  • zxcvbn
  • zxcxz
  • zzz
  • zzzz
  • zzzzz


Note: Depending on the account lockout settings, multiple authentication attempts by the worm may result in those accounts becoming locked out.

If successful, the worm copies itself to the share as the following file:
[SHARE NAME]\ADMIN$\System32\[RANDOM FILE NAME].dll

It then creates a scheduled job on the remote server to run daily consisting of the following command:
"rundll32.exe [RANDOM FILE NAME].dll, [RANDOM PARAMETER STRING]"

Next, the worm connects to the following URLs to obtain the IP address of the compromised computer:
  • [http://]www.getmyip.org
  • [http://]www.whatsmyipaddress.com
  • [http://]getmyip.co.uk
  • [http://]checkip.dyndns.org


The worm creates a firewall rule on the local network gateway device that allows remote attackers to connect to and download from the compromised computer's external IP address through a random port.

The worm then creates an HTTP server on the compromised computer on a random port in the following format:
http://[COMPROMISED COMPUTER EXTERNAL IP ADDRESS]:[RANDOM PORT]

It then sends this URL to remote computers.

The worm then attempts to spread by exploiting the following vulnerability so that remote computers will connect to the above named URL and download the worm:
Microsoft Windows Server Service RPC Handling Remote Code Execution Vulnerability (BID 31874)

The worm then attempts to copy itself to any accessible mapped drive as the following file:
%DriveLetter%\RECYCLER\S-%d-%d-%d-%d%d%d-%d%d%d-%d%d%d-%d\[RANDOM FILE NAME].dll

The worm also attempts to create the following file on any accessible mapped drive so that it executes whenever the drive is accessed:
%DriveLetter%\autorun.inf

It also monitors the compromised computer for any additional new drives and then attempts to infect any newly added drives in the same way.

The worm hooks a number of Windows API calls in order to spread and to make removal more difficult.

The worm also hooks the NetpwPathCanonicalize API and when it is called, it checks the length of PathName in order to avoid exploiting the vulnerability further. If the PathName contains a signature the worm originally has, the PathName may contain an encrypted URL as well from which the worm may download a file and execute it.

The worm patches the following API's in memory:
  • DNS_Query_A
  • DNS_Query_UTF8
  • DNS_Query_W
  • Query_Main
  • sendto


The worm monitors DNS requests to domains containing any of the following strings and blocks access to these domains so that it appears that the network request timed out:
  • ahnlab
  • arcabit
  • avast
  • avg.
  • avira
  • avp.
  • bit9.
  • ca.
  • castlecops
  • centralcommand
  • cert.
  • 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
  • nai.
  • networkassociates
  • nod32
  • norman
  • norton
  • panda
  • pctools
  • prevx
  • quickheal
  • rising
  • rootkit
  • sans.
  • securecomputing
  • sophos
  • spamhaus
  • spyware
  • sunbelt
  • symantec
  • threatexpert
  • trendmicro
  • vet.
  • virus
  • wilderssecurity
  • windowsupdate


It contacts one of the following sites to get the current date:
  • baidu.com
  • google.com
  • yahoo.com
  • msn.com
  • ask.com
  • w3.org
  • aol.com
  • cnn.com
  • ebay.com
  • msn.com
  • myspace.com


It then checks to see whether the date on the compromised computer is on or after January 1, 2009.

The worm will then generate a list of domain names based upon this date in the following format:
[GENERATED DOMAIN NAME].[TOP LEVEL DOMAIN]

Note: [TOP LEVEL DOMAIN] represents the following top level domains:
  • .biz
  • .info
  • .org
  • .net
  • .com
  • .ws
  • .cn
  • .cc


Note: [GENERATED DOMAIN NAME] represents the domain names created by the worm such as the following example list of domain names generated for January 1, 2009:
  • aaidhe.net
  • aamkn.cn
  • abivbwbea.info
  • aiiflkgcw.cc
  • alfglesj.info
  • amcfussyags.net
  • amzohx.ws
  • apaix.ws
  • argvss.info
  • arolseqnu.ws
  • asoidakm.cn
  • atnsoiuf.cc
  • avweqdcr.cn
  • axaxmhzndcq.cc
  • barhkuuu.com
  • bbuftxpskw.cc
  • bdykhlnhak.cc
  • bdzpfiu.biz
  • bijkyilaugs.cn
  • bjpmhuk.ws
  • bmmjbsjidmt.com
  • bzagbiwes.cc
  • carse.cn
  • cauksxf.biz
  • cfhlglxofyz.biz
  • cinsns.cc
  • ciynbjwm.com
  • cljivsb.biz
  • cpeadyepcis.biz
  • cqnxku.ws
  • ctmchiae.ws
  • cxjsy.net
  • czkdu.net
  • dbffky.cn
  • dgbdjsb.com
  • drpifjfxlyl.ws
  • dtosuhc.org
  • duahpzq.org
  • dwrtwgsm.cn
  • dyjomzyz.com
  • earuldx.cn
  • egqoab.net
  • egxbsppn.cn
  • ehkvku.cn
  • elivvks.net
  • emxmg.info
  • eobvidij.org
  • erwojl.org
  • evqvmwgw.cn
  • ewioygq.biz
  • exxkvcz.cc
  • ffaqk.info
  • fhlwov.net
  • fitjg.net
  • fkhbumne.info
  • fknacmvowib.cn
  • fmdsqasqm.net
  • fmgcjv.cn
  • fpljpuqp.info
  • fsrljjeemkr.info
  • fthil.cc
  • ftphtsfuv.net
  • gbgklrka.cc
  • gbmkghqcqy.net
  • gbxyu.ws
  • gezjwr.biz
  • gjbwolesl.info
  • glkzckadwu.biz
  • gmvhjp.ws
  • gsvrglz.cc
  • gutvjbektzq.com
  • gwtqx.cn
  • hbyzvpeadkb.net
  • hewdw.ws
  • hjcxnhtroh.cn
  • hltowx.com
  • hqjazhyd.com
  • hrmirvid.com
  • hudphigb.org
  • hvagbqmtxp.info
  • idvgqlr.ws
  • ihnvoeprql.biz
  • iidqkzselpr.com
  • ijthszjlb.com
  • iklzskqoz.cn
  • iqgnqt.org
  • iqrzamxo.ws
  • isjjlnv.org
  • iudqzypn.cn
  • iyfcmcaj.cn
  • jayrocykoj.ws
  • jffhkvhweds.cn
  • jfxcvnnawk.org
  • jgrftgunh.org
  • jguxjs.net
  • jhanljqti.cc
  • jhvlfdoiyn.biz
  • jjhajbfcdmk.net
  • jkisptknsov.biz
  • jknxcxyg.net
  • jlouqrgb.org
  • jpppffeywn.cc
  • jradvwa.biz
  • juqsiucfrmi.net
  • jvnzbsyhv.org
  • jxnyyjyo.net
  • kaonwzkc.info
  • kdcqtamjhdx.ws
  • kgeoaxznfms.biz
  • kihbccvqrz.net
  • kimonrvh.org
  • kjsxwpq.ws
  • kkrxwcjusgu.cn
  • knqwdcgow.ws
  • koaqe.cc
  • kodzhq.org
  • kqjvmbst.net
  • kufvkkdtpf.net
  • kxujboszjnz.ws
  • lagcrxz.cc
  • lawwb.com
  • lbdfwrbz.net
  • ljizrzxu.cc
  • lmswntmc.biz
  • lotvecu.com
  • lplsebah.cn
  • lxhmwparzc.ws
  • lyamwnhh.info
  • mciuomjrsmn.cn
  • mdntwxhj.cn
  • meqyeyggu.cc
  • mfigu.cn
  • mimdezm.biz
  • mkdsine.cn
  • mmtdsgwfa.net
  • mouvmlhz.cc
  • mozsj.biz
  • mpqzwlsx.ws
  • msvhmlcmkmh.biz
  • mtruba.ws
  • myrmifyuqo.biz
  • naucgxjtu.ws
  • ncwjlti.cn
  • nertthl.net
  • nnxqqmdl.info
  • nuxtzd.cn
  • nxvmztmryie.ws
  • nybxvgb.net
  • nzsrgzmhay.net
  • oadscrk.org
  • oezepyh.info
  • ojrswlg.net
  • olgjkxih.org
  • omqxqptc.ws
  • ooudifyw.cn
  • opkawiqb.cn
  • oqsfz.ws
  • orvfkx.cc
  • otoajxfn.net
  • oxeeuikd.net
  • oyezli.com
  • pfath.info
  • plsexbnytn.com
  • poplie.cc
  • psbdfflh.cn
  • qfmbqxom.ws
  • qjvtczqu.com
  • qpcizvlvio.biz
  • qslhoks.cn
  • qtcnfvf.biz
  • qtsnk.cn
  • qzktamrsgu.cn
  • rbhixtifxk.cc
  • rccoq.net
  • rgievita.ws
  • rlrbqpxv.org
  • rozhtnmoudg.cc
  • rpsctacalyd.cn
  • rrmkv.com
  • rtpuqxp.net
  • rtztoupc.net
  • satmxnz.ws
  • sbtalilx.com
  • sdjnaeoh.cc
  • sirkqq.org
  • sjkkfjcx.biz
  • sjkxyjqsx.net
  • stmsoxiguz.net
  • tdeghkjm.biz
  • tkhnvhmh.biz
  • tmdoxfcc.org
  • torhobdfzit.cc
  • trdfcxclp.org
  • tscmbj.net
  • tuwcuuuj.com
  • txeixqeh.biz
  • uazwqaxlpq.info
  • ubxxtnzdbij.com
  • ucnfehj.org
  • uekmqqedtfm.com
  • uhtmou.ws
  • uhveiguagm.biz
  • uoieg.ws
  • uttcx.net
  • uyhgoiwswn.cc
  • uyvtuutxm.cn
  • vfxifizf.info
  • vupnwmw.biz
  • vzqpqlpk.ws
  • waeqoxlrprp.org
  • wdrvyudhg.cc
  • wediscbpi.org
  • whgtdhqg.net
  • wkstxvzr.org
  • wmrgzac.info
  • wnwqphzao.info
  • wsajx.com
  • wskzbakqfvk.org
  • wtngipaynh.info
  • wumvjpbbmse.cc
  • wuzunxevor.info
  • wwftlwlvm.org
  • xcncp.info
  • xeeuat.com
  • xhazhbir.biz
  • xjnyfwt.org
  • xlrqvoqmsxz.info
  • xqgbn.cn
  • xwrrxwmo.cc
  • xxabrkhb.cc
  • xxmgkcw.cc
  • xxxxgvtaa.com
  • xzoycphicpk.com
  • ybbfrznr.info
  • ycceqdmm.cc
  • ydxnochqn.org
  • ygmwharv.info
  • ylnytttckyc.com
  • yuvudlsdop.cc
  • ywhaunsyez.cc
  • ywxdggnaaad.org
  • zindtsqq.ws
  • zkywmqx.com
  • zoosmv.info
  • zqekqyq.cn
  • zqked.org
  • zsatn.ws
  • ztgsd.info
  • ztioydng.com
  • zzczpujz.biz

The worm then contacts the following remote location based on the domain names generated:
http://[GENERATED DOMAIN NAME].[TOP LEVEL DOMAIN]/search?q=%d

It will then download an updated copy of itself from the above remote location.

The worm may also receive and execute files through a peer-to-peer mechanism by communicating with other compromised computers. These files would need to be seeded into the network of worms by the malware author.

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: Sean Kiernan
Summary| Technical Details| Removal

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