TROJ_COREM.A

October 09, 2012
 Analysis by: Jasen Sumalapao
 ALIASES:

Trojan:Win32/Coremhead (Microsoft), Trojan.Win32.Yakes.aldl (Kaspersky), Trojan.Gen.2 (Symantec), PWS-Zbot.gen.yl (NAI), Troj/Katush-Gen (Sophos), Lookslike.Win32.Sirefef.j (v) (Sunbelt), TR/Kazy.84637.1 (Antivir), W32/Falab.F.gen!Eldorado (Authentium), Gen:Variant.Kazy.84456 (Bitdefender), W32/Kryptik.YLA!tr (Fortinet), W32/Falab.F.gen!Eldorado (generic, not disinfectable) (Fprot), Trojan.Win32.Yakes (Ikarus), a variant of Win32/Kryptik.AJKA trojan (NOD32), BScope.Trojan-Ransom.Winlock.6812 (VBA32)

 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:

60,928 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Aug 2012

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 files:

  • %User Temp%\7af3996f

(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.)

It is injected into the following processes running in memory:

  • svchost.exe

Other System Modifications

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

HKEY_CLASSES_ROOT\CLSID\{B0B32503-B325-2503-B325-0B32B0B32503}

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
CLSID\{B0B32503-B325-2503-B325-0B32B0B32503}

HKEY_USERS\.DEFAULT\Software\
Microsoft\Windows\CurrentVersion\
Internet Settings\Connections
DefaultConnectionSettings = "{random value}"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}.{BLOCKED}.199.201

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.332.05

FIRST VSAPI PATTERN DATE:

19 Aug 2012

VSAPI OPR PATTERN File:

9.333.00

VSAPI OPR PATTERN Date:

20 Aug 2012

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Search and delete this file

[ Learn More ]
There may be some component files 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%\7af3996f

Step 4

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_CLASSES_ROOT\CLSID
    • {B0B32503-B325-2503-B325-0B32B0B32503}
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID
    • {B0B32503-B325-2503-B325-0B32B0B32503}

Step 5

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_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections
    • DefaultConnectionSettings = "{random value}"

Step 6

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