TROJ_NECURS.BGSH

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 listens on ports.

It connects to certain websites to send and receive information. It deletes the initially executed copy of itself.

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 copies of itself into the affected system:

• %Windows%\Installer\{random GUID}\syshost.exe - if logged in as an Administrator
• %Application Data%\{random GUID}\syshost.exe - 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 creates the following folders:

• %Windows%\Installer\{random GUID} - if logged in as an Administrator
• %Application Data%\{random 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 terminates the execution of the copy it initially executed and executes the copy it drops instead.

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
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32
ImagePath = ""%Windows%\Installer\{random GUID}\syshost.exe" /service"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32
ObjectName = "LocalSystem"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\syshost32
Type = "10"

It adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
syshost32 = "%Application Data%\{random GUID}\syshost.exe" (if not logged in as an Administrator)

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

Backdoor Routine

This Trojan listens on the following ports:

• TCP port 26809
• UDP port 26809

Other Details

This Trojan connects to the following website to send and receive information:

• http://{BLOCKED}.{BLOCKED}.81.244
• http://{BLOCKED}.{BLOCKED}.195.245
• http://{BLOCKED}.{BLOCKED}.56.54
• http://{BLOCKED}.{BLOCKED}.31.41

It deletes the initially executed copy of itself

NOTES:

This Trojan attempts to delete the following files:

• %Windows%\Installer\{random GUID}\syshost.exe:Zone.Identifier (if logged in as an Administrator)
• %Application Data%\{random CLSID}\syshost.exe:Zone.Identifier (if not logged in as an Administrator)

It only creates the service if the current logged on user is an Administrator.