F-Secure Virus Descriptions : Graps

NAME:	Graps
ALIAS:	Worm.Win32.Graps, W32/Graps.worm, W32.HLLW.Graps

Graps worm was discovered in the beginning of July 2003. This worm spreads in local networks. It scans a network for vulnerable computers and tries to get access the IPC$ and ADMIN$ shares by performing a dictionary attack (using a set of pre-defined weak passwords to get access). If the worm succeeds, it copies itself to remote computer, activates its file and deletes IPC$ and ADMIN$ shares.

Technical Description

The worm is a 53kb Windows PE executable file written in Visual Basic and compressed with UPX file compressor. The worm spreads itself with the help of the following files:

 psexec.exe - a utility that allows to run processes on remote computers
 mswinsck.ocx - standard WinSock library for VB applications
 wds.bat  \
 wds2.bat  - batch files that spread the worm to remote computers (dropped by the worm)
 wds3.bat /
 mwd.exe - the worm's executable file

The batch scripts that the worm drop are used to get access to IPC$ and ADMIN$ share protected by a weak password or no password at all. When such a share is discovered, the scripts copy the worm's main file mwd.exe and also psexec.exe and mswinsck.ocx files to \ADMIN$\System32\ folder (which is a Windows System folder on a remote computer) and start the worm's file remotely with psexec.exe utility. As a result a remote computer becomes infected with the worm. After spreading the worm tries to delete IPC$ and ADMIN$ shares.

On an infected computer the worm creates a startup key for its file in System Registry:

 [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run]
 "Windows Management Instumentation" = "%winsysdir%\mwd.exe"

The worm has a few additional features. It listens to the specific port and can allow remote hackers to log into it and perform the following actions:

 - perform DoS (Denial of Service) attack
 - get system information
 - search for specified files on a hard disk
 - redirect traffic (works as a proxy)
 - scan for open ports

To disinfect a system it's enough to delete mwd.exe file and 3 above mentioned batch files from a hard disk.

Detection

Detection for Graps worm is available since the following FSAV updates:

[FSAV_Database_Version]

Version=2003-07-08_03

[Description: F-Secure Anti-Virus Research Team; F-Secure Corp.; July 8th, 2003]