BKDR_GENTAB.JI

October 17, 2012
 Analysis by: Jaime Benigno Reyes
 ALIASES:

TrojanDownloader:Win32/Kuluoz.B (Microsoft), Trojan.Fakeavlock (Norton), Generic Downloader.z (McAfee), Troj/Agent-YEQ (Sophos)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 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 itself after execution.

  TECHNICAL DETAILS

File Size:

52,736 bytes

File Type:

EXE

Memory Resident:

Yes

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 a copy of itself in the following folders using different file names:

  • %Application Data%\{random file name}.exe

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

It drops the following file(s)/component(s):

  • %Current Folder%\{malware file name}.TXT

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random subkey name} = "%Application Data%\{random file name}.exe"

Other System Modifications

This backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\{random key}

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}5.{BLOCKED}4.75.185:84
  • http://{BLOCKED}3.{BLOCKED}4.211.194:8080
  • http://{BLOCKED}4.{BLOCKED}1.67.199:8080
  • http://{BLOCKED}8.{BLOCKED}7.103.54:8080
  • http://{BLOCKED}4.{BLOCKED}4.20.226:8080
  • http://{BLOCKED}8.{BLOCKED}5.212.160:8080
  • http://{BLOCKED}8.{BLOCKED}2.156.180:8080
  • http://{BLOCKED}2.{BLOCKED}9.224.202:8080
  • http://{BLOCKED}3.175.218.180:8080
  • http://{BLOCKED}3.{BLOCKED}5.218.181:8080
  • http://{BLOCKED}7.{BLOCKED}0.236.108:84
  • http://{BLOCKED}6.{BLOCKED}5.112.99:8080
  • http://{BLOCKED}0.{BLOCKED}2.136.150:8080
  • http://{BLOCKED}8.{BLOCKED}6.31.53:8080
  • http://{BLOCKED}7.{BLOCKED}0.236.108:84

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.456.04

FIRST VSAPI PATTERN DATE:

12 Oct 2012

VSAPI OPR PATTERN File:

9.457.00

VSAPI OPR PATTERN Date:

13 Oct 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 BKDR_GENTAB.JI

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Search and delete the file detected as BKDR_GENTAB.JI

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 5

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.
  • %Current Folder%\{malware file name}.TXT

Step 6

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 subkey name} = "%Application Data%\{random file name}.exe"

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_GENTAB.JI. 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 key HKEY_CURRENT_USER\Software\{random key} cannot be identified by the users since there are no reference values in the created key. The only way it can be identified is by comparing the present keys with a backup if the users have one. Note that the key, {random key} need not to be deleted since it won't cause the user system any harm.


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