Analysis by: Michael Cabel
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • 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 executes then deletes itself afterward.

However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 208,215 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 31 Jul 2011

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 executes then deletes itself afterward.

Other System Modifications

This backdoor adds the following registry keys as part of its installation routine:

HKEY_CLASSES_ROOT\Interface\{91137ba5-45d2-d8ad-576f-6beda9ed3a94}

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}ur.cn/{BLOCKED}t2.php?w=15&i={random characters}&a=1
  • http://{BLOCKED}ur.cn/{BLOCKED}d.php?w=15&fail=1&i={random characters}
  • http://{BLOCKED}ur.cn/{BLOCKED}at2.php?w=15&i={random characters}&a=21
  • http://{BLOCKED}ur.cn/{BLOCKED}t2.php?w=15&i={random characters}&a=20

However, as of this writing, the said sites are inaccessible.

  SOLUTION

Minimum Scan Engine: 8.900
FIRST VSAPI PATTERN FILE: 8.322.03
FIRST VSAPI PATTERN DATE: 31 Jul 2011

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

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_CLASSES_ROOT\Interface
    • {91137ba5-45d2-d8ad-576f-6beda9ed3a94}

Step 3

Scan your computer with your Trend Micro product to delete files detected as BKDR_ZACCESS.BB. 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.


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