Class Virus
Platform SWScript

Technical Details

text written by Costin Raiu, Kasperskys, Romania

This is the first virus known to infect Macromedia Shockwave (.SWF) files,
which are commonly used for various kinds of animations on the World Wide
Web; for instance in animated e-cards or e-greetings. The virus does not
work if an infected Shockwave .SWF file is loaded in the player plugin
distributed with most newer versions of the Netscape and Internet Explorer
browsers – it will only execute and replicate if the user manually loads
infected animation into the stand-alone Shockwave Flash Player application,
which greatly limits the danger posed by the virus to most computer users.
At this time, there have not been any reports of this
virus “in-the-wild,” and we do not expect it to ever become widespread.

Technical details

The virus works by taking advantage of the scripting language available in
Shockwave animations – it is itself stored as a Shockwave script that
further drops a DOS .COM executable named “V.COM” that is 926 bytes long. The DOS
executable is dropped to disk through a standard DEBUG script, but this
will only work on Windows NT, 2000 and XP systems, because the dropper
script attempts to call the command line preprocessor as “cmd.exe”, which
is not available on Win9X/ME installations. When executed, the V.COM
program will search for all the *.SWF files in the current directory, make
sure they are not read-only, hidden or system, so they can be written to, and
it will attempt to infect them. First, it will check whether they have the
standard “FWSx99” signature, and if so, the virus will proceed to create a
new Shockwave script dropper similar to the one used to initially drop the
“V.COM” executable to disk. The Shockwave script dropper is created in a
piece of dynamically allocated memory, and is written at the beginning of
the target Shockwave file.