Analysis by: Abraham Latimer Camba

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

It drops copies of itself into all the removable drives connected to an affected system. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It connects to certain URLs. It may do this to remotely inform a malicious user of its installation. It may also do this to download possibly malicious files onto the computer, which puts the computer at a greater risk of infection by other threats.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size: 87,552 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 11 Jul 2012

Arrival Details

This Trojan arrives via removable drives.

It 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 and executes them:

  • %User Profile%\Application Data\KB{random number}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
KB{random number}.exe = "%User Profile%\Application Data\KB{random number}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\{random hex string 1}

HKEY_CURRENT_USER\Software\Microsoft\
Windows NT\{random hex string 2}

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
GlobalUserOffline = "0"

Propagation

This Trojan drops copies of itself into all the removable drives connected to an affected system.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[autorun]
open={Malware Path and File Name}.exe
shell\Open\Command={Malware Path and File Name}.exe
shell\Open\Default=1
shell\Explore\Command={Malware Path and File Name}.exe
shell\Autoplay\command={Malware Path and File Name}.exe

Download Routine

This Trojan connects to the following malicious URLs:

  • http://{Random URL}:8080/za/v_01_a/in/

Other Details

This Trojan deletes the initially executed copy of itself

NOTES:

This worm uses a domain generation algorithm to generate random domains.

  SOLUTION

Minimum Scan Engine: 9.200
FIRST VSAPI PATTERN FILE: 9.250.03
FIRST VSAPI PATTERN DATE: 11 Jul 2012
VSAPI OPR PATTERN File: 9.251.00
VSAPI OPR PATTERN Date: 12 Jul 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

Scan your computer with your Trend Micro product and note files detected as WORM_CRIDEX.TN

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.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT
    • {random hex string 1}
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows NT
    • {random hex string 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
    • KB{random number}.exe = "%User Profile%\Application Data\KB{random number}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • GlobalUserOffline = "0"

Step 6

Search and delete AUTORUN.INF files created by WORM_CRIDEX.TN that contain these strings

[ Learn More ]
 
    [autorun]
    open={Malware Path and File Name}.exe
    shell\Open\Command={Malware Path and File Name}.exe
    shell\Open\Default=1
    shell\Explore\Command={Malware Path and File Name}.exe
    shell\Autoplay\command={Malware Path and File Name}.exe

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_CRIDEX.TN. 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 hex string 1} and HKEY_CURRENT_USER\Software\Microsoft\Windows NT\{random hex string 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 to be deleted since these won't cause the user system any harm.


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