BKDR_ZXSHELL.B
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
Downloaded from the Internet, Dropped by other malware
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 may be dropped by other malware.
It executes then deletes itself afterward.
It executes commands from a remote malicious user, effectively compromising the affected system. However, as of this writing, the said sites are inaccessible.
TECHNICAL DETAILS
500,192 bytes
EXE
Yes
25 Jun 2015
Collects system information
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.
It may be dropped by the following malware:
- CHM_ZXSHELL.B
Installation
This backdoor drops the following component file(s):
- %System%\WinUser.dat (detected as BKDR_ZXSHELL.B)
(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)
It drops and executes the following files:
- %System%\mscorsv.dll (detected as BKDR_ZXSHELL.B)
(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)
It adds the following processes:
- rundll32.exe
It executes then deletes itself afterward.
Autostart Technique
This backdoor creates the following service using its DLL component:
- 6to4
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- end current task
- run arbitrary files
- show help
- share shell to other
- send system info
- Download or upload files via ftp
- Uninstall
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- {BLOCKED}pan.{BLOCKED}s.info
However, as of this writing, the said sites are inaccessible.
Information Theft
This backdoor gathers the following data:
- OS version
- disk space
- RAM
- host name
- organization
- registered organization
- owner
- registered owner
- drive list and description
SOLUTION
9.750
11.752.05
25 Jun 2015
11.753.00
26 Jun 2015
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
Restart in Safe Mode
Step 4
Restart in Safe Mode, and then delete this registry key
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\CurrentControlSet\Services
- 6to4
- 6to4
Step 5
Remove the malware/grayware file that dropped/downloaded BKDR_ZXSHELL.B. (Note: Please skip this step if the threat(s) listed below have already been removed.)
- CHM_ZXSHELL.B
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ZXSHELL.B. 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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