Analysis by: Al Victor de Leon

ALIASES:

TrojanDropper:Win32/Sirefef.B (Microsoft), PWS-Zbot.gen.vv (McAfee), Trojan-Dropper.Win32.ZAccess.gh (Kaspersky), Trojan-Dropper.Win32.ZAccess (Ikarus), Win32/Sirefef.DB (Eset), BackDoor.Generic_s.A (AVG), Win32:Sirefef-TT [Trj] (Avast)

 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: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

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

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.

It opens random ports. It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 214,016 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 06 Jun 2012
Payload: Compromises system security, Drops files

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:

  • %Windows%\$NtUninstallKB{GUID}$\{random numbers}\Desktop.ini

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

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

  • %Windows%\$NtUninstallKB{GUID}$\{random number}\L\{random character} - detected as TROJ_SIREFEF.PM
  • %Windows%\$NtUninstallKB{GUID}$\{random numbers}\@
  • %Windows%\$NtUninstallKB{GUID}$\{random number }\cfg.ini

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

It creates the following folders with attributes set to System and Hidden to prevent users from discovering and removing its components:

  • %Windows%\$NtUninstallKB{GUID}$\{random number}\L
  • %Windows%\$NtUninstallKB{GUID}$
  • %Windows%\$NtUninstallKB{GUID}$\{random number}

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

It injects itself into the following processes as part of its memory residency routine:

  • winlogon.exe

Autostart Technique

This Trojan registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\System\ControlSet001\
Services\.afd
ImagePath = \?

Backdoor Routine

This Trojan opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

It executes the following commands from a remote malicious user:

  • send - send information to the CnC server
  • recv - receive file or code

It connects to the following websites to send and receive information:

  • http://{BLOCKED}s.{BLOCKED}g .com/geo/txt/city.php
  • http://{random 8 characters}.cn/stat2.php?w={integer}&i={integer}&a={integer}

Other Details

This Trojan deletes itself after execution.

NOTES:

It patches selected system drivers located in "%System%\drivers\". However, it avoid the following drivers:

  • classpnp.sys
  • win32k.sys

The patched SYS file is detected as PTCH_ZACCESS.SMF.

It searches for the following services in the system and deletes the services once found:

  • windefend
  • iphlpsvc
  • wscsvc
  • mpssvc
  • bfe

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.158.04
FIRST VSAPI PATTERN DATE: 07 Jul 2014
VSAPI OPR PATTERN File: 10.159.00
VSAPI OPR PATTERN Date: 07 Jul 2014

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

Remove grayware/spyware files dropped/downloaded by TROJ_SIREFEF.VUI

    •  TROJ_SIREFEF.PM

Step 3

Scan your computer with your Trend Micro product and note files detected as TROJ_SIREFEF.VUI

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_LOCAL_MACHINE\System\ControlSet001\Services
    • .afd

Step 5

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.
  • %Windows%\$NtUninstallKB{GUID}$

Step 6

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

Step 7

Restore these deleted files from backup

*Note: Only Microsoft-related keys/values will be restored. If this malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

  • windefend
  • iphlpsvc
  • wscsvc
  • mpssvc
  • bfe
  •  


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