Threat Description

Stream

Details

Aliases: Stream, Win2k_Stream, Win2K.Stream
Category: Malware
Type: Virus
Platform: W32

Summary



The Win2k.Stream virus was not found in the wild at the moment of creation of this description.The Win2k.Stream is the first known Windows virus using a "stream companion" infection method. This method is based on NTFS feature that allows a creation of multiple data streams associated with a file.



Removal



Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.



Technical Details



On NTFS system, each file contains at least one default data stream that is accessed just by file name. Each file may also contain additional stream(s) that can be accessed by their personal names (filename:streamname).The default file stream is the file body itself (in pre-NTFS terms). For instance, when an EXE file is executed, the program is read from the default file stream; when a document is opened, its contents are also read from the default stream.Additional file streams may contain any data. The streams cannot be accessed or modified without reference to the file. When a file is deleted, its streams are deleted as well; if a file is renamed, streams follow its new name.Windows package does not have any standard tools to view/edit file streams. You need to use special utilites to "manually" view file streams, for instance FAR utility with the file steams support plug-in (Ctrl-PgDn displays file streams for the selected file).The virus itself is a Windows application (PE EXE file), compressed by Petite PE EXE files compressor and it is about 4K long. When run, it infects all EXE files in the current directory and then returns control to the host file. If any error occurs, the virus displays the message:

While infecting the file, the virus creates a new stream associated with the victim file. That stream has "STR" name, i.e. complete stream name is "FileName:STR". The virus then moves the STR stream to the victim file body (default stream, see above) and then overwrites the victim file body (default stream) with its (virus) code.As a result, when the infected file is executed Windows reads the default stream (that is overwritten by the virus code) and executes it. Also, Windows reports the same file size for all infected files - which is the virus length.The virus creates a new process by accessing the original file program with "FileName:STR" name to release control to host program.This infection method should work on any NTFS system, but the virus checks system version and runs only under Win2000.





Technical Details: Eugene Kaspersky, KL; September 2000


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