TROJ_NECURS.TENJ
Trojan:Win32/Necurs (Microsoft), Trojan-Dropper.Win32.Necurs.val (Kaspersky)
Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)
Threat Type: Trojan
Destructiveness: No
Encrypted:
In the wild: Yes
OVERVIEW
This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.
It is injected into all running processes to remain memory resident.
It modifies registry entries to disable the Windows Firewall settings. This action allows this malware to perform its routines without being deteted by the Windows Firewall.
It creates an event. It deletes the initially executed copy of itself.
TECHNICAL DETAILS
94,208 bytes
EXE
No
10 Jun 2014
Disables Windows Firewall, Connects to URLs/IPs
Arrival Details
This Trojan 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 Trojan drops the following component file(s):
- %System%\drivers\{random}.sys - detected as RTKT_NECURS.AH
(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)
It drops the following copies of itself into the affected system:
- %Application Data%\{GUID}\syshost.exe - if not logged in as an Administrator
- %Windows%\Installer\{GUID}\syshost.exe - if logged in as an Administrator
(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.. %Windows% is the Windows folder, which is usually C:\Windows.)
It creates the following folders:
- %Windows%\Installer\{GUID} - if logged in as an Administrator
- %Application Data%\{GUID} - if not logged in as an Administrator
(Note: %Windows% is the Windows folder, which is usually C:\Windows.. %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)
It is injected into all running processes to remain memory resident.
Autostart Technique
This Trojan 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\syshost32
ImagePath = ""%Windows%\Installer\{GUID}\syshost.exe" /service"
It adds the following registry entries to enable its automatic execution at every system startup:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
syshost32 = "%Windows%\Installer\{GUID}\syshost.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\syshost32
It registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random}
Other System Modifications
This Trojan modifies the following registry entries to disable the Windows Firewall settings:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAcces\Parameters\
FirewallPolicy\DomainProfile
EnableFirewall = "0"
Other Details
This Trojan connects to the following URL(s) to check for an Internet connection:
- Facebook.com
- Microsoft.com
It creates the following event(s):
- Global\NitrGB
- Local\NitrGB
It deletes the initially executed copy of itself
NOTES:
It performs a netsh.exe command that disables Windows Firewall depending on the OS version. It elevates certain privileges when not in Administrator mode.
It connects to the following site to send and receive data:
- http://{BLOCKED}.{BLOCKED}8.90.136/forum/db.php
The received data is written to a file in the %User Temp% folder.
However, as of this writing, no data was received from the server.
SOLUTION
9.700
10.850.04
09 Jun 2014
10.851.00
09 Jun 2014
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
Remove the malware/grayware file dropped/downloaded by TROJ_NECURS.TENJ. (Note: Please skip this step if the threat(s) listed below have already been removed.)
- RTKT_NECURS.AH
Step 3
Restart in Safe Mode
Step 4
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\SYSTEM\CurrentControlSet\Services\syshost32
- ImagePath = ""%Windows%\Installer\{GUID}\syshost.exe" /service"
- ImagePath = ""%Windows%\Installer\{GUID}\syshost.exe" /service"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
- syshost32 = "%Windows%\Installer\{GUID}\syshost.exe"
- syshost32 = "%Windows%\Installer\{GUID}\syshost.exe"
Step 5
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
- syshost32
- syshost32
- In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
- {random}
- {random}
Step 6
Restore this modified 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\SYSTEM\CurrentControlSet\Services\SharedAcces\Parameters\FirewallPolicy\DomainProfile
- From: EnableFirewall = "0"
To: EnableFirewall = "1"
- From: EnableFirewall = "0"
Step 7
Search and delete these folders
- %Windows%\Installer\{GUID} - if logged in as an Administrator
- %Application Data%\{GUID} - if not logged in as an Administrator
Step 8
Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_NECURS.TENJ. 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.
Did this description help? Tell us how we did.