Analysis by: Sabrina Lei Sioting
ALIASES:

Win32:Careto-A [Spy] (Avast), Win32/Appetite.A (Eset), Backdoor:W32/Mask.A (FSecure), W32/Careto.A!tr (Fortinet), Backdoor.Mask (Ikarus), Trojan.Win32.Careto.b (Kaspersky), Trojan:Win32/Seedna.A (Microsoft), Trj/Careto.A (Panda), Backdoor.Weevil (Symantec),

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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.

  TECHNICAL DETAILS

File Size: Varies
File Type: EXE, DLL
Memory Resident: Yes
Initial Samples Received Date: 18 Feb 2014

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.

Other System Modifications

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

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{E6BB64BE-0618-4353-9193-0AFE606D6F0C}\InprocServer32
{default} = "%System%\browseui.dll"

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{E6BB64BE-0618-4353-9193-0AFE606D6F0C}\InprocServer32
ThreadingModel = "Apartment"

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{ECD4FC4D-521C-11D0-B792-00A0C90312E1}\InprocServer32
{default} = %System%\{objframe.dll or shmgr.dll} (Windows 2000 or Windows XP)"

HKEY_LOCAL_MACHINE\Software\Classes\
CLSID\{ECD4FC4D-521C-11D0-B792-00A0C90312E1}\InprocServer32
{default} = "%AppData%\Microsoft\{objframe.dll or shmgr.dll} (Windows Vista, 7 or 8)"

NOTES:

This backdoor has an embedded encrypted .CAB file which contains the files shlink32.dll and Shlink64.dll.

This backdoor saves the file shlink32.dll if the system is 32-bit depending on the platform/operating system of the affected computer as the following:

  • %System%\{objframe.dll or shmgr.dll} (Windows 2000 or Windows XP)
  • %AppData%\Microsoft\{objframe.dll or shmgr.dll} (Windows Vista, 7 or 8)

It also saves the file Shlink64.dll if the system is 64-bit depending on the platform/operating system of the affected computer as the following:

  • %System%\{objframe.dll or shmgr.dll} (Windows 2000 or Windows XP)
  • %AppData%\Microsoft\{objframe.dll or shmgr.dll} (Windows Vista, 7 or 8)

  SOLUTION

Minimum Scan Engine: 9.700

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 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\Classes\CLSID\{E6BB64BE-0618-4353-9193-0AFE606D6F0C}\InprocServer32
    • {default} = "%System%\browseui.dll"
  • In HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{E6BB64BE-0618-4353-9193-0AFE606D6F0C}\InprocServer32
    • ThreadingModel = "Apartment"
  • In HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{ECD4FC4D-521C-11D0-B792-00A0C90312E1}\InprocServer32
    • {default} = "%System%\{objframe.dll or shmgr.dll} (Windows 2000 or Windows XP)"
  • In HKEY_LOCAL_MACHINE\Software\Classes\CLSID\{ECD4FC4D-521C-11D0-B792-00A0C90312E1}\InprocServer32
    • {default} = "%AppData%\Microsoft\{objframe.dll or shmgr.dll} (Windows Vista, 7 or 8)"

Step 4

Search and delete this file

[ Learn More ]
There may be some 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.
%System%\{objframe.dll or shmgr.dll}
%AppData%\Microsoft\{objframe.dll or shmgr.dll}

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_CARETO.B. 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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