Summary

Rugrat is a simple direct-action file infector that targets 64-bit Windows executables, 32-bit applications are not affected. This virus only infects files in the current directory of the infected executable and all of its subdirectories.

Additional Details

Rugrat is the first known virus that targets the 64-bit Windows platform. The size of the virus suggests that it was hand-written in IA64 assembly.

Rugrat uses the Thread Local Storage feature of Windows executables to gain execution. It adds a TLS entry to the executable which contains a callback pointer to the virus code. This has the unusual side effect that often the virus will run only after the host has exited, which is exactly opposite to the way parasitic infectors are normally activated.

The virus code is a minimal direct-action infector routine. It first imports a number of Windows API functions using checksums.

From NTDLL.DLL:

 LdrGetDllHandle
 RtlAddVectoredExceptionHandler
 RtlRemoveVectoredExceptionHandler

which are used to install a Vectored Exception Handler to catch all exceptions during the infection process.

From KERNEL32.DLL the usual functions are imported:

 CloseHandle
 CreateFileMappingA
 CreateFileW
 FindClose
 FindFirstFileW
 FindNextFileW
 GetFullPathNameW
 GetTickCount
 GlobalAlloc
 GlobalFree
 LoadLibraryA
 MapViewOfFile
 SetCurrentDirectoryW
 SetFileAttributesW
 SetFileTime
 UnmapViewOfFile

From SFC_OS.DLL Rugrat imports the function

 SfcIsFileProtected

which it uses to check whether the executable it tries to infect is protected by the System File Checker (SFC) service of Windows. The virus does not try to infect SFC-protected executables.

Rugrat uses a simple method of infection. It sets the last section (which is often the resources section) executable and copies itself there. A random number of zero bytes are also appended to the end of the virus body.

Rugrat contains two strings that are never displayed:

Reference to the author: 'Shrug - roy g biv'

Possibly the creation date: '06/05/04'

Detection

Detection for this malware was published on May 27th, 2004 in the following F-Secure Anti-Virus updates:

[FSAV_Database_Version]
Version=2004-05-27_02

Technical Details: Gergely Erdelyi, July 1st, 2004;

F-Secure Corporation