Analysis by: Rhena Inocencio

ALIASES:

TrojanDownloader:Win32/Cutwail.BS (Microsoft)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 May 2013

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

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

  • %User Profile%\{random filename}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

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

  • {random filename}

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random filename} = "%User Profile%\{random filename}.exe"

Other System Modifications

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
AppManagement = "{random values}"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion
{random filename}zap = "{random values}"

Propagation

This backdoor uses any of the following Simple Mail Transfer Protocol (SMTP) servers:

  • smtp.compuserve.com
  • mail.airmail.net
  • smtp.directcon.net
  • smtp.sbcglobal.yahoo.com
  • smtp.mail.yahoo.com
  • smtp.live.com

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Download and execute files
  • Retrieve Spam Configuration/Content
  • Get OS Version
  • Get System Information
  • Get Network Information

It connects to the following websites to send and receive information:

  • {BLOCKED}ta.org

NOTES:

It performs random GET Request connection to the following URLs to mask outbound connections:

  • 0daymusic.biz
  • 0kommanix.de
  • 0kommanix.de
  • 0risiko.de
  • 4-elements.ch
  • 4-elements.ch
  • 4-elements.ch
  • 4darabians.nl
  • 4darabians.nl
  • 4dbabamozi.hu
  • 4dbabamozi.hu
  • 4dbabamozi.hu
  • 4dbenelux.be
  • 4dbenelux.be
  • 4effect.ca
  • 4egolifestyle.de
  • 4elementos.cl
  • 4elements.cz
  • 4elements.hu
  • 4elements.pl
  • 4emails.de
  • 4emotion.pl
  • 4enerchi.nl
  • 4energia.ee
  • 4ernila.de
  • 4erotik.de
  • 4erotik.de
  • 4esport.de
  • 4estates.eu
  • 4ever-hosting.de
  • 4ever4you.de
  • 4everandever.de
  • 4everevents.nl
  • 4everkids.de
  • 4evernails.nl
  • 4every1.cc
  • 4every1.cc
  • 4everything.pl
  • 8wellesley.ca
  • 8zaamarchitecten.nl
  • 8zaamarchitecten.nl
  • 8zaamarchitecten.nl
  • 9online.fr
  • 9t6grafikdesign.de
  • 9welten.de
  • accountingtechs.biz
  • accountingtechs.biz
  • accountingtechs.biz
  • accounting.ee
  • accounting.ee

It performs random POST Request connection to the following URLs to mask outbound connections. It may also randomly add the URI /?ptrxcz_{random} to domains below:

  • abv.bg
  • actuslendlease.com
  • adt.com
  • aeroinc.net
  • alice-dsl.de
  • allstate.com
  • allstate.com
  • aol.com.com
  • apollo.lv
  • atkearney.com
  • atkearney.com
  • backaviation.com
  • backpacker.com
  • bailliegifford.com
  • bailliegifford.com
  • bassettfurniture.com
  • birds.com
  • birds.com
  • boardermail.com
  • bol.com.br
  • brick.net
  • btopenworld.com
  • buffalo.edu
  • bumbleandbumble.com
  • bumbleandbumble.com
  • cablelynx.com
  • cablelynx.com
  • cableone.net
  • cableone.net
  • caionline.org
  • cancun.com.mx
  • cannylink.com
  • cantv.net
  • capecod.net
  • caramail.com
  • carolina.com
  • catech-systems.com
  • centurytel.net
  • chat4all.org
  • chickensys.com
  • clarksville.com
  • cnet.com
  • col.com
  • comcast.net
  • comporium.net
  • connections-etc.net
  • connections-etc.net
  • correoweb.com
  • cox.com
  • cox.net
  • croeso.com
  • crosspaths.net
  • dadlnet.dk
  • diamondcpu.com
  • diamondcpu.com
  • diamondcpu.com
  • dicksmail.com
  • dr.dk
  • dragonmount.com
  • dsl.com
  • eastlink.ca
  • eastlink.ca
  • enter.net
  • excite.co.jp
  • excite.co.uk
  • excite.co.uk
  • excite.fr
  • eznet.net
  • frg.eur.nl
  • gallatinriver.net
  • gallatinriver.net
  • gmx.at
  • grayfoot.mailshell.com
  • happemail.com
  • happyhippo.com
  • hotmaik.com
  • hotmale.com
  • hotmiail.com
  • idealcollectables.com
  • imaginet.com
  • in.com
  • intuit.com
  • iowatelecom.net
  • iupui.edu
  • iw.com
  • iw.com
  • juno.net
  • karoo.co.uk
  • kettering.edu
  • kettering.edu
  • laposte.net
  • machlink.com
  • madasfish.com
  • mania.com
  • mania.com
  • marchmail.com
  • merck.com
  • merck.com
  • metallica.com
  • metrocast.net
  • military.com
  • military.com
  • mindspring.com
  • models.com
  • mountainmax.net
  • mountainmax.net
  • mountainmax.net
  • msn.net
  • music.com
  • musician.org
  • mweb.co.za
  • myway.com
  • nau.edu
  • ncable.net.au
  • ncable.net.au
  • nccn.net
  • neobright.net
  • netscape.com
  • netscape.net
  • nifty.com
  • ninemsn.com.au
  • ninemsn.com.au
  • nsatel.net
  • o2.co.uk
  • oakwood.org
  • olemiss.edu
  • onebox.com
  • ono.com
  • ono.es
  • oregonstate.edu
  • planttel.net
  • plasa.com
  • popstar.com
  • posten.se
  • potamkinmitsubishi.com
  • primeline.com
  • primusonline.com.au
  • proftools.lt
  • pru-nw.com
  • quixnet.net
  • redlands.edu
  • reihtec.com
  • reihtec.com
  • robvivian.com
  • robvivian.com
  • rz-online.de
  • rz-online.de
  • schoolsports.com
  • sexstories.com
  • sify.com
  • sky.com
  • skynet.be
  • sol.dk
  • spin.com
  • spray.se
  • spray.se
  • sscomputing.com
  • start.no
  • stupid.com
  • su.edu
  • suscom.net
  • sympatico.com
  • t-mobel.com
  • tartarus.uwa.edu.au
  • terra.cl
  • terra.com.br
  • the-beach.net
  • tigers-net.com
  • tinet.org
  • tiscali.co.uk
  • trib.com
  • tylerknott.com
  • uakron.edu
  • uakron.edu
  • ufl.edu
  • ufl.edu
  • und.edu
  • univision.com
  • vail.com
  • vaxxine.com
  • verizon.net
  • verizon.net
  • verizon.net
  • virginia.edu
  • vol.com
  • vol.com
  • vwr-inc.com
  • wa-net.com
  • wagged.com
  • waupacafoundry.com
  • wildmail.com
  • world-net.co.nz
  • www.optonline.com
  • x-men.com
  • x-men.com
  • yahoo.co.jp
  • yahoo.com.cn
  • zdnetonebox.com
  • zeelandnet.nl
  • zueliya.com

The sent OS Version information is any of the following format:

  • UndefinedOS
  • Vista
  • Win2K
  • Win7
  • Win8
  • WinHomeServer
  • WinServer2003R2
  • WinServer2008
  • WinServer2003
  • WinServer2012
  • WinServer2008R2
  • WinXP
  • WinXP64

  SOLUTION

Minimum Scan Engine: 9.300

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Scan your computer with your Trend Micro product and note files detected as BKDR_PUSHDO.SM

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random filename} = "%User Profile%\{random filename}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • AppManagement = "{random values}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion
    • {random filename}zap = "{random values}"

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_PUSHDO.SM. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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