Virus.Win32.RemEx

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: Virus

Viruses replicate on the resources of the local machine. Unlike worms, viruses do not use network services to propagate or penetrate other computers. A copy of a virus will reach remote computers only if the infected object is, for some reason unrelated to the virus function, activated on another computer. For example: when infecting accessible disks, a virus penetrates a file located on a network resource a virus copies itself to a removable storage device or infects a file on a removable device a user sends an email with an infected attachment.

Read more

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

Technical Details

The virus is quite large in size - it is written in Microsoft Visual C++ and is about 125K. The original virus code occupies about 14K, GZIP routines - 20K, C run-time libraries - 40K. Other data areas are occupied by virus/C++ data, resources, etc.

The virus has quite an unusual structure: the infected files have code and data segments, as well as three resources that contain compressed executable files. The first resource contains the standard NT4 PSAPI.DLL that is used by the virus to access processes in the system memory.

The second resource is the original virus code itself (including the same compressed PSAPI.DLL in the resource). This copy of virus code is used as the original data to install the virus into the system and to infect EXE files.

The third resource is the host file that is extracted and decompressed, when the virus needs to run the host program.

System Registry: while installing its SYS driver to the system the virus uses the standard NT API calls. This causes the system to register the virus drivers in the system registry - the HKEY_LOCAL_MACHINESystemCurrentControlSetServicesRemote Explorer is created.

Temporary files: while compressing/decompressing files the virus needs temporary ones. It creates them in the Windows temporary directory with the random names ~xxxdddd.TMP (where 'x' are letters and 'd' are digits).

Resume

The virus is the first native "memory resident" NT infector, so it might look as some super-virus. Actually the virus was written by some middle-level developer who had access to the NT DeviceDevelopmentKit documentation.

The virus does not hook any NT event, does not use any network protocols, does not try to access the passwords, and does not spread its copy over the global network. Moreover, the ordinary DOS parasitic viruses have the same network spreading abilities like this virus has - they also can infect files on remote shared drives, stay in the system memory, etc.

This is just a standard parasitic virus, but with NT service infection ability. It is not more complex than some other already known Windows viruses, and definitely not more complex than the well-known BO trojan (BackOrifice).

This virus is not a shock at all - it is long awaited WindowsNT-service virus.

Read more

Find out the statistics of the vulnerabilities spreading in your region on statistics.securelist.com