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Threat Encyclopedia

TROJ_ZLOB


ALIASES:

DNSChanger

PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type:Trojan

  • Destructiveness:No

  • Encrypted:

  • In the wild: Yes

OVERVIEW

Infection Channel:

Downloaded from the Internet


ZLOB malware has been around since 2006. It is known to arrive on computers posing as a video codec. As this malware family expanded, some incidents recorded by Trend Micro noted its arrival via compromised websites.

ZLOB malware's main function is to change the DNS settings of the computers it infects. Changing the DNS settings of the computers allows ZLOB to redirect the systems to malicious sites. In effect, money is indirectly stolen by cybercriminals as the traffic intended for legitimate sites are redirected to other sites.

Some ZLOB variants are known to monitor browsing activities. Others are capable of terminating security-related processes - an attempt to avoid early detection and removal from an affected computer.

TECHNICAL DETAILS

Memory Resident:

Yes

Payload:

Connects to URLs/IPs, Modifies system registry, Steals information, Terminates processes

Installation

This Trojan drops the following files:

  • %System%\spool\prtprocs\w32x86\{random}.dll
  • %System%\ernel32.dll

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

It drops the following copies of itself into the affected system:

  • %System%\spool\PRTPROCS\W32X86\000029cc.tmp
  • %User Temp%\{random}
  • %System%\{random}.exe
  • %Application Data%\{random}.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.. %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.. %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_MSWU-B04BA347

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_MSWU-B04BA347\
0000

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MSWU-b04ba347

Other System Modifications

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLUA = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Security Center
UacDisableNotify = "1"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\DomainProfile\AuthorizedApplications\
List
%System%\spoolsv.exe = "%System%\spoolsv.exe:*:Enabled:spoolsv.exe"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters
NameServer = "{BLOCKED}.{BLOCKED}.162.160,{BLOCKED}.{BLOCKED}.166.191"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters
DhcpNameServer = "{BLOCKED}.{BLOCKED}.162.160,{BLOCKED}.{BLOCKED}.166.191"

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

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters\
Interfaces\{CLSID}
DhcpNameServer = "{BLOCKED}.{BLOCKED}.162.160.{BLOCKED}.{BLOCKED}.166.191"

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

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}ume.com/kx.php
  • http://{control URL}/index.asp
  • http://{control URL}/dlink/hwiz.html
  • http://{control URL}/home.asp
  • http://{control URL}/wizard.htm
  • http://{control URL}/login.asp
  • http://{BLOCKED}.{BLOCKED}.90.26/bsfd.php

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