19.03.2009

Trojan.Skimer

Risk Level 1: Very Low



Discovered: March 18, 2009
Updated: March 19, 2009 8:53:51 AM
Type: Trojan
Infection Length: 79,872 bytes
Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows NT, Windows Server 2003, Windows Vista, Windows XP

SUMMARY

Trojan.Skimer is a Trojan horse that opens a back door and steals information from compromised Automated Teller Machines (ATMs).

Protection

  • Initial Rapid Release version March 18, 2009 revision 055
  • Latest Rapid Release version March 19, 2009 revision 001
  • Initial Daily Certified version March 19, 2009 revision 005
  • Latest Daily Certified version March 19, 2009 revision 005
  • Initial Weekly Certified release date March 25, 2009

Threat Assessment

Wild

  • Wild Level: Low
  • Number of Infections: 0 - 49
  • Number of Sites: 0 - 2
  • Geographical Distribution: Low
  • Threat Containment: Easy
  • Removal: Easy

Damage

  • Damage Level: Medium
  • Payload: Opens a back door
  • Deletes Files: Deletes Windows prefetch files
  • Releases Confidential Info: Steals information, including account details and PINs
  • Compromises Security Settings: Compromises ATM control flow

Distribution

  • Distribution Level: Low

TECHNICAL DETAILS

When executed, the Trojan copies itself as the following file:
%Windir%\lsass.exe

It then attempts to copy the file %Windir%\trl2 as one of the following files:
  • %Windir%\greenstone.bmp:redstone.bmp (if the file system is in NTFS format)
  • %Windir%\redstone.bmp (if the file system is in any other format)

It then attempts to copy the file %Windir%\kl as one of the following files:
  • %Windir%\greenstone.bmp:bluestone.bmp (if the file system is in NTFS format)
  • %Windir%\bluestone,bmp (if the file system is in any other format)

Note: The above files may be used to store information gathered from the compromised ATM.

It then injects itself into the following process:
explorer.exe

It then attempts to delete all files with the following names:
%Windir%\Prefetch\-[ASCII CHARACTERS].pf

The Trojan monitors the compromised computer for processes with the following names:
  • mu.exe
  • SpiService.exe

When found, the Trojan hooks API functions in the above processes so that it can alter the behavior of the ATM.

The Trojan may attempt to log transaction and PIN information to the following file:
%ProgramFiles%\Diebold\AMI\AMITRACE\AMITrace.txt

When logging account balance information, the Trojan converts account balances to US dollars using the following conversion rates:
  • 26 Russian rubles : 1 US dollar
  • 5 Ukrainian hryvnias : 1 US dollar

The Trojan may open a back door on the compromised ATM to allow an attacker to perform the following actions via the keypad:
  • Display the logged information
  • Print the logged information using the ATM printer
  • Display the ATM software version
  • Dispense cash
  • Uninstall the Trojan horse
  • Shut down the ATM

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.