WORM_DOWNAD.AC

Infection Channel:

Propagates via flashdrives, Copies itself in all available logical drives, Propagates via network shares

This worm arrives via removable drives. It may be dropped by other malware.

It modifies registry entries to disable various system services. This action prevents most of the system functions to be used. It deletes registry entries, causing some applications and programs to not function properly.

It drops copies of itself into all the removable drives connected to an affected system. It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system. It exploits software vulnerabilities to propagate to other computers across a network.

It uses certain lists of user names and passwords to access password-protected shared files.

It prevents users from visiting antivirus-related websites that contain specific strings.

File Size:

166,111 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

05 Apr 2016

Payload:

Compromises system security, Compromises network security

Arrival Details

This worm arrives via removable drives.

It may arrive via network shares.

It may be dropped by other malware.

Installation

This worm drops the following copies of itself into the affected system:

%Application Data%\{random file name}.dll
%System%\{random file name}.dll
%System%\{random number}.tmp
%Program Files%\Internet Explorer\{random file name}.dll
%Program Files%\Movie Maker\{random file name}.dll
%User Temp%\{random file name}.dll

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming 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.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.. %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.. %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.)

Autostart Technique

This worm 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\{random characters}
DisplayName = "{random}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
Type = "32"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
Start = "2"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
ErrorControl = "0"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
ObjectName = "Local System"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
Description = "{long sentences}"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}
ImagePath = "%System Root%\system32\svchost.exe -k netsvcs"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{random characters}\Parameters
ServiceDll = "%System%\{malware file name}"

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random characters} = "rundll32.exe {malware path and file name}, {Parameter}"

Other System Modifications

This worm adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Applets
dl = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Applets
ds = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets
ds = "0"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets
dl = "0"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Tcpip\Parameters
TcpNumConnections = "0x00FFFFFE" - hex values

(Note: The default value data of the said registry entry is {System Default}.)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
netsvcs = "{original value} {random characters}"

(Note: The default value data of the said registry entry is {original value}.)

It modifies registry entries to disable the following system services:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv
Start = "4"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\WinDefend
Start = "4"