BKDR_POISON.AAZ

October 09, 2012
 Analysis by: Mark Joseph Manahan
 ALIASES:

Win32/Poison trojan (Eset)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows 7

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users. 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 deletes itself after execution.

  TECHNICAL DETAILS

File Size:

503,901 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

10 Sep 2012

Arrival Details

This backdoor arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

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 backdoor drops the following copies of itself into the affected system:

  • %User Profile%\Application Data\AdstreamStr.exe (for accounts without Admin Rights)
  • %System%:AdstreamStr.exe (for accounts with Admin Rights)
  • %User Profile%\AppData\Roaming:AdstreamStr.exe (for Windows Vista/Windows 7 only)

(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.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

This backdoor creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
AdobePhoto streamStr = "%User Profile%\Application Data\AdstreamStr.exe" (for accounts without Admin Rights)

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
AdobePhoto streamStr = "%System%:AdstreamStr.exe" (for accounts with Admin Rights)

HKEY_CURRENT_USER\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
AdobePhoto streamStr = "%User Profile%\AppData\Roaming:AdstreamStr.exe" (for Windows Vista/Windows 7 only)

Backdoor Routine

This backdoor connects to the following URL(s) to send and receive commands from a remote malicious user:

  • tw.{BLOCKED}arleft.com
  • hk.{BLOCKED}arleft.com

Other Details

This backdoor deletes itself after execution.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

9.384.03

FIRST VSAPI PATTERN DATE:

10 Sep 2012

VSAPI OPR PATTERN File:

9.385.00

VSAPI OPR PATTERN Date:

11 Sep 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

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_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • AdobePhoto streamStr = "%User Profile%\Application Data\AdstreamStr.exe" (for accounts without Admin Rights)
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • AdobePhoto streamStr = "%System%:AdstreamStr.exe" (for accounts with Admin Rights)
  • In HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • AdobePhoto streamStr = "%User Profile%\AppData\Roaming:AdstreamStr.exe" (for Windows Vista/Windows 7 only)

Step 4

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_POISON.AAZ. 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:

Remove the Alternate Data Stream from this file

To remove the Alternate Data Stream:

  1. Download Streams.exe from this Microsoft page. Extract the contents of this file to a location of your choice.
  2. Open a command prompt window.Click Start>Run, type CMD, then press Enter.
  3. In the command prompt, type the following, then press Enter:
    CD {Path where contents of downloaded file was extracted}
  4. Still in the command prompt type the following then press Enter:
    Streams.exe -d %System%
    Streams.exe -d %User Profile%\AppData\Roaming
  5. Type exit then press Enter.


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