BKDR_SMALL.USCZ
Mal/Behav-143 (Sophos); Suspicious.DLoader (Symantec)
Windows
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 does not have any propagation routine.
It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.
It gathers certain information on the affected computer.
TECHNICAL DETAILS
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 the following files:
- %User Temp%\{random}_tmp.cmd
(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)
It adds the following mutexes to ensure that only one of its copies runs at any one time:
- T2015010901
- T2015012802
Propagation
This backdoor does not have any propagation routine.
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- Gather Information
- Get Drives Information
- Get File Information
- Find Files
- Create Folder
- Execute Files
- Move File
- Create Files
- Modify Files
- Empty Recycle Bin
- Terminate Process
- Shutdown
- Send Gathered Information
- Perform Remote Shell
- Sleep
It connects to the following websites to send and receive information:
- http://{BLOCKED}z.{BLOCKED}l.net/{random values}.{random format}
- https://{BLOCKED}z.{BLOCKED}l.net/{random values}.{random format}
where {random format} may be any of the following:- asp
- php
- jsp
- aspx
- htm
- html
- shtm
- shtml
- cgi
- xml
As of this writing, the said sites are inaccessible.
Information Theft
This backdoor gathers the following information on the affected computer:
- Volume Information
- Computer Name
- User Name
- OS Version
- Drive Information
- File Information
SOLUTION
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
Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.
Step 3
Identify and terminate files detected as BKDR_SMALL.USCZ
- Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
- If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
- If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.
Step 4
Search and delete this file
- %User Temp%\{random}_tmp.cmd
Step 5
Scan your computer with your Trend Micro product to delete files detected as BKDR_SMALL.USCZ. 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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