Analysis by: Jimelle Monteser
ALIASES:

Trojan.Win32.Bublik (Ikarus), Trojan.Win32.Bublik.axsp (Kaspersky), Worm:Win32/Cridex (Microsoft), W32.Cridex (Norton)

 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:

  • 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 deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 285,696 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 08 Jun 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:

  • %Application Data%\KB{random numbers}.exe

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

It creates the following folders:

  • %Application Data%\{random folder name}

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

Autostart Technique

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

HKCU\Software\Microsoft\
Windows\CurrentVersion\Run
{random file name}.exe = "%Application Data%\KB{random numbers}.exe"

Other System Modifications

This backdoor adds the following registry keys:

HKCU\Software\Microsoft\
Windows NT\{random value 1}

HKCU\Software\Microsoft\
Windows NT\{random value 2}

Other Details

This backdoor connects to the following possibly malicious URL:

  • {BLOCKED}.{BLOCKED}.3.246
  • {BLOCKED}.{BLOCKED}.74.5
  • {BLOCKED}.{BLOCKED}.138.172

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.972.04
FIRST VSAPI PATTERN DATE: 10 Jun 2013
VSAPI OPR PATTERN File: 9.973.00
VSAPI OPR PATTERN Date: 11 Jun 2013

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_CRIDEX.MJM

Step 3

Restart in Safe Mode

[ Learn More ]

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.

  • HKCU\Software\Microsoft\Windows NT\{random value 1}
  • HKCU\Software\Microsoft\Windows NT\{random value 2}

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random file name}.exe = "%Application Data%\KB{random numbers}.exe"

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data%\{random folder name}

Step 7

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

NOTES:

The created registry keys HKEY_CURRENT_USER\Software\Microsoft\Windows NT\{random value 1} and HKEY_CURRENT_USER\Software\Microsoft\Windows NT\{random value 2} cannot be identified by the users since there are no reference values in the created keys.

The only way these keys can be identified is by comparing the present keys with a backup if the users have one. Note that these keys need not be deleted since it won't cause the user system any harm.


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