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TROJ_ZEGOST.SAA

June 04, 2013
 ALIASES:

BackDoor-EXZ (McAfee); Backdoor.Trojan (Symantec); Trojan-Dropper.Win32.Small.p (Kaspersky); Trojan-Dropper.Win32.Resdro.b (v) (not malicious) (Sunbelt); Fat-Obfuscated (AVG)

 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

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

  TECHNICAL DETAILS

File Size:

1,414,549 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

04 Jun 2013

Arrival Details

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

  • %User Temp%\~__UNINST.EXE

(Note: %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.)

Autostart Technique

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{jdcxefml-btle-iimh-nglc-fprbencbrejy}
stubpath = "%System%\inlsmacbt.exe"

It 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\
Services\PCRatStact

Other System Modifications

This Trojan deletes the following files:

  • %User Temp%\~pmThis.tmp

(Note: %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 registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\{jdcxefml-btle-iimh-nglc-fprbencbrejy}

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Services\PCRatStact
Type = "12"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\Session Manager\SFC
ProgramFilesDir = "%Program Files%"

(Note: The default value data of the said registry entry is %Program Files%.)

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\
Control\Session Manager\SFC
CommonFilesDir = "%Program Files%\Common Files"

(Note: The default value data of the said registry entry is %Program Files%\Common Files.)

It deletes the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Active Setup\Installed Components\{jdcxefml-btle-iimh-nglc-fprbencbrejy}

Dropping Routine

This Trojan drops the following files:

  • %User Temp%\½º´Ô¸ñŹ.exe
  • %User Temp%\½º´Ô.exe
  • %System%\inlsmacbt.exe
  • %System%\syslog.dat
  • %User Temp%\103687_res.tmp
  • %User Temp%\~pmThis.tmp

(Note: %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.. %System% is the Windows system folder, which is usually C:\Windows\System32.)

This report is generated via an automated analysis system.

  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

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ 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_LOCAL_MACHINE\SYSTEM\CurrentControlSEt\Services
    • PCRatStact
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components
    • {jdcxefml-btle-iimh-nglc-fprbencbrejy}

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{jdcxefml-btle-iimh-nglc-fprbencbrejy}
    • stubpath = "%System%\inlsmacbt.exe"
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Services\PCRatStact
    • Type = "12"

Step 5

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\SFC
    • From: ProgramFilesDir = "%Program Files%"
      To: ProgramFilesDir = ""%Program Files%""
  • In HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\SFC
    • From: CommonFilesDir = "%Program Files%\Common Files"
      To: CommonFilesDir = ""%Program Files%\Common Files""

Step 6

Search and delete these components

[ Learn More ]
There may be some components that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %User Temp%\½º´Ô¸ñŹ.exe
  • %User Temp%\½º´Ô.exe
  • %System%\inlsmacbt.exe
  • %System%\syslog.dat
  • %User Temp%\103687_res.tmp
  • %User Temp%\~pmThis.tmp

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_ZEGOST.SAA. 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.

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %User Temp%\~pmThis.tmp

Step 9

Restore these deleted registry keys/values from backup

*Note: Only Microsoft-related keys/values will be restored. If the malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • In HKEY_CURRENT_USER\Software\Microsoft\Active Setup\Installed Components
    • {jdcxefml-btle-iimh-nglc-fprbencbrejy}


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