BKDR_ZEGOST.YNQC
Backdoor:Win32/Zegost.BZ(Microsoft), a variant of Win32/Farfli.BKX trojan(Eset)
Windows
Threat Type: Backdoor
Destructiveness: No
Encrypted: Yes
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 commands from a remote malicious user, effectively compromising the affected system.
It deletes itself after execution.
TECHNICAL DETAILS
190,480 bytes
EXE
Yes
09 Mar 2015
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 copies of itself into the affected system and executes them:
- %System%\{random 6 letters}.exe
(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)
Autostart Technique
This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tu3vwxy Bcdefghi Klm
ImagePath = "%System%\{random 6 letters}.exe"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tu3vwxy Bcdefghi Klm
DisplayName = "Tuvwxy Bcdefghi Klmnopqr Tu3vw"
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tu3vwxy Bcdefghi Klm
Description = "Tuvwxy Bcdefghi Klmnopqr Tu3vw"
It adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
{random 6 letters} = "%System%\{random 6 letters}.exe"
It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tu3vwxy Bcdefghi Klm
Backdoor Routine
This backdoor executes the following commands from a remote malicious user:
- Logs Keystroke
- Capture screenshot
- Logs Mouse event
- Gather CPU information
- Start remote desktop connection
- Create hidden administrative user
It connects to the following URL(s) to send and receive commands from a remote malicious user:
- wo521.{BLOCKED}2.org
Other Details
This backdoor deletes itself after execution.
SOLUTION
9.750
11.528.05
09 Mar 2015
11.529.00
10 Mar 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
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
- Tu3vwxy Bcdefghi Klm
- Tu3vwxy Bcdefghi Klm
Step 5
Delete this registry value
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\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- {random 6 letters} = "%System%\{random 6 letters}.exe"
- {random 6 letters} = "%System%\{random 6 letters}.exe"
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_ZEGOST.YNQC. 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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