The virus, MSH/Cibyz, targets Windows PowerShell. It was released last week by the RRLF virus group. PowerShell is a command-line shell and task-based scripting technology that provides control and administration of system administration tasks. It is supposed to eventually replace the Windows default command interpreter shell, but is not yet installed by default.
MSH/Cibyz is a shell script virus using the same infection methods as other shells. According to Avert Labs researchers, "It cannot achieve memory residency nor possess rootkit capabilities, however malicious code written in Windows PowerShell can be modified to drop a Win32 executable on an infected system to achieve the above mentioned features."
The researchers add that because Windows PowerShell allows users "to do anything one can do from the graphical user interface via a command line shell, it makes it an attractive platform for malware authors to write next-generation viruses."
This is the third proof-of-concept virus targeting Vista that members of the RRLF group have released in the past year, after MSH/Danom and W32/Usined (alias MSIL/Idonus).
"The ones before this were not nearly as sophisticated as this one," says Allysa Myers, a McAfee virus research engineer. "This shows the continuing interest among the virus-writing community in this scripting language."
Myers says solution providers should counsel their customers that threats can come from a much wider array of sources than just .exe files.
"Users seem to think that only certain types of files can hurt you, but they need to look at the greater whole; you need to be aware of what files you're receiving and only open ones that you're expecting," Myers says. "The lines of safety are getting blurrier and blurrier, so having multiple layers of defense is very important."