Worm.Win32.Stuxnet

Parent class: VirWare

Viruses and worms are malicious programs that self-replicate on computers or via computer networks without the user being aware; each subsequent copy of such malicious programs is also able to self-replicate. Malicious programs which spread via networks or infect remote machines when commanded to do so by the “owner” (e.g. Backdoors) or programs that create multiple copies that are unable to self-replicate are not part of the Viruses and Worms subclass. The main characteristic used to determine whether or not a program is classified as a separate behaviour within the Viruses and Worms subclass is how the program propagates (i.e. how the malicious program spreads copies of itself via local or network resources.) Most known worms are spread as files sent as email attachments, via a link to a web or FTP resource, via a link sent in an ICQ or IRC message, via P2P file sharing networks etc. Some worms spread as network packets; these directly penetrate the computer memory, and the worm code is then activated. Worms use the following techniques to penetrate remote computers and launch copies of themselves: social engineering (for example, an email message suggesting the user opens an attached file), exploiting network configuration errors (such as copying to a fully accessible disk), and exploiting loopholes in operating system and application security. Viruses can be divided in accordance with the method used to infect a computer:

• file viruses
• boot sector viruses
• macro viruses
• script viruses

Any program within this subclass can have additional Trojan functions. It should also be noted that many worms use more than one method in order to spread copies via networks.

Class: Worm

Worms spread on computer networks via network resources. Unlike Net-Worms, a user must launch a Worm in order for it to be activated. This kind of worm searches remote computer networks and copies itself to directories that are read/write accessible (if it finds any). Furthermore, these worms either use built-in operating system functions to search for accessible network directories and/or they randomly search for computers on the Internet, connect to them, and attempt to gain full access to the disks of these computers. This category also covers those worms which, for one reason or another, do not fit into any of the other categories defined above (e.g. worms for mobile devices).

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Platform: Win32

Win32 is an API on Windows NT-based operating systems (Windows XP, Windows 7, etc.) that supports execution of 32-bit applications. One of the most widespread programming platforms in the world.

Description

Using the driver:

%System%driversmrxnet.sys

The rootkit connects as a driver filter to the following file system arrangements:

FileSystemntfs



FileSystemfastfat



FileSystemcdfs

and thereby obtains control of the infected computer's file system. The rootkit hides files with names like this:

~WTR<rnd>.tmp

where <rnd> is a random four-digit number, e.g.:

~WTR4132.tmp



~WTR4141.tmp

It also hides files with the extension LNK and a file size equal to 4171 bytes. The rootkit file has a Realtek Semiconductor Corp digital signature. It contains the following string:

b:myrtussrcobjfre_w2k_x86i386guava.pdb

Using the driver:

%System%driversmrxcls.sys

The malicious program injects malicious code into the user mode's processes. To do this, it loads a DLL dynamic library into the following system processes:

svchost.exe



services.exe



lsass.exe

after which, their module lists contain libraries with names like this:

kernel32.dll.aslr.<rnd>



shell32.dll.aslr.<rnd>

where <rnd> is a random hexadecimal number. The injected code is found in the file:

%WinDir%infoem7A.PNF

in encrypted form.

The injected code contains the malicious program's main functionality. This includes:

• Propagation via removable media.
• Monitoring for the operation of the Siemens Step7 system. To do this, the rootkit driver injects its intermediary library to the process s7tgtopx.exe, replacing the original s7otbxsx.dll, which emulates the operation of the following API functions:

  
  
  
  s7_event
  
  
  
  s7ag_bub_cycl_read_create
  
  
  
  s7ag_bub_read_var
  
  
  
  s7ag_bub_write_var
  
  
  
  s7ag_link_in
  
  
  
  s7ag_read_szl
  
  
  
  s7ag_test
  
  
  
  s7blk_delete
  
  
  
  s7blk_findfirst
  
  
  
  s7blk_findnext
  
  
  
  s7blk_read
  
  
  
  s7blk_write
  
  
  
  s7db_close
  
  
  
  s7db_open
  
  
  
  s7ag_bub_read_var_seg
  
  
  
  s7ag_bub_write_var_seg
  
  
  
  

  collecting various information about how the system works.
• Execution of SQL requests. The malware obtains a list of computers on the local network and checks whether any of them is currently running Microsoft SQL Server, which serves the process visualization system Siemens WinCC. If the server is detected, the malware attempts to connect to the database with the username and password WinCCConnect/2WSXcder (CVE-2010-2772), after which it attempts to obtain information about tables, such as:

  
  
  
  MCPTPROJECT
  
  
  
  MCPTVARIABLEDESC
  
  
  
  MCPVREADVARPERCON
  
  
  
  

• It collects information from files with the following extensions:

  
  
  
  *.S7P
  
  
  
  *.MCP
  
  
  
  *.LDF
  
  
  
  

  These are created through the Siemens Step7 system. A search for files is carried out on the whole of the computer's hard disk.
• It sends the collected information via the Internet to the malicious user's server in encrypted form.

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