Linux.Simile

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Discovered: May 22, 2002
Updated: February 13, 2007 11:57:34 AM
Also Known As: W32.Simile, {Win32, Linux}/Simile.D, {Win32, Linux}/Etap.D
Type: Virus
Systems Affected: Linux, Windows


{Win32,Linux}/Simile.D is a very complex virus that uses entry-point obscuring, metamorphism, and polymorphic decryption. It is the first known polymorphic metamorphic virus to infect under both Windows and Linux. The virus contains no destructive payload, but infected files may display messages on certain dates. It is the fourth variant of the Simile family. This variant introduces a new infection mechanism on Intel Linux platforms, infecting 32-bit ELF files (a standard Unix binary format). The virus infects Portable Executable (PE) files as well as ELFs on both Linux and Win32 systems. So far Symantec has not received any submissions of this virus from customers.

NOTE: The {Win32,Linux} reference follows the CARO (Computer Anti-virus Researchers Organization) standard naming convention. This is meant to imply that a threat can infect across multiple platforms, Win32 and Linux. Another such example would be {Win32,W97M}.



Norton AntiVirus detects the virus as W32.Simile in infected PE files and as Linux.Simile in infected ELF files. As a result, we have two different platform identifiers for this virus and detect the family of this virus under a single generic name without the usual variant letters in the name.

Portable Executable (PE) files
PE files are files that are portable across all Microsoft 32-bit operating systems. The same PE-format executable can be executed on any version of Windows 95, 98, Me, NT, and 2000. Therefore, all PE files are executable, but not all executable files are portable.

A good example of a Portable Executable is a screen saver (.scr) file.

Antivirus Protection Dates

  • Initial Rapid Release version May 30, 2002
  • Latest Rapid Release version May 30, 2002
  • Initial Daily Certified version May 30, 2002
  • Latest Daily Certified version May 30, 2002
  • Initial Weekly Certified release date June 05, 2002

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Frederic Perriot

Discovered: May 22, 2002
Updated: February 13, 2007 11:57:34 AM
Also Known As: W32.Simile, {Win32, Linux}/Simile.D, {Win32, Linux}/Etap.D
Type: Virus
Systems Affected: Linux, Windows


When the virus is first executed, it checks the current date.

  • If the date is March 17 or September 17, and the virus host is a PE file, it displays this message:


  • If the date is March 17 or May 17, and the virus host is an ELF file, the virus attempts to output a text message to the console. The message will be similar to the following:



The first Win32/Linux cross-infector, {Win32,Linux}/Peelf, uses two separate routines to carry out the infection on PE and ELF files. This variant of Simile shares a substantial amount of code between the two infection functions, such as the polymorphic/metamorphic engines, the only platform-specific parts being the directory traversal code and the API usage.

The virus was confirmed to infect successfully under versions 6.2, 7.0 and 7.2 of Red Hat Linux, and it very likely works on most other common Linux distributions.

Infected files will grow by about 110 KB on average, but the size increase is variable due to the shrinking and expansion capability of the metamorphic engine and to the insertion method.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Frederic Perriot

Discovered: May 22, 2002
Updated: February 13, 2007 11:57:34 AM
Also Known As: W32.Simile, {Win32, Linux}/Simile.D, {Win32, Linux}/Etap.D
Type: Virus
Systems Affected: Linux, Windows


To remove this Trojan, update the virus definitions, run a full system scan, and delete all files that are detected as W32.Simile or Linux.Simile. For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and repair the infected files:

  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as W32.Simile or Linux.Simile. Replace deleted files from a clean backup or reinstall them.


Writeup By: Frederic Perriot