Antivirus software companies have warned of an e-mail
worm that targets unpatched Microsoft Windows machines with either
of two recently disclosed software vulnerabilities.
The worm, known as both "Plexus" and "Explet.A", was first
detected last week and spreads by exploiting Windows machines with
vulnerabilities used by two recent worms, Sasser and Blaster.
Network Associates' McAfee Antivirus Emergency Response Team and
Symantec both said the new worm does not pose a serious threat, but
have issued software updates to detect it.
Plexus exploits the Windows component called Local Security
Authority Subsystem Service, or LSASS, which Microsoft patched in
April. Plexus can also crawl through a hole in a Windows component
called the DCOM (Distributed Component Object Model) interface,
which handles messages sent using the RPC (remote procedure call)
protocol. (See
http://www.microsoft.com/technet/security/bulletin/MS03-026.mspx
and
http://www.microsoft.com/technet/security/bulletin/MS04-011.mspx.)
Plexus spreads in files attached to e-mail messages with faked
sender addresses and vague subjects such as "RE: order," "For you"
and "Good offer".
When users open the virus file, the worm is launched and alters
the configuration of Windows so that the worm program runs each
time Windows starts. It also scans the hard drive of infected
computers, harvesting e-mail addresses from a variety of files,
including stored web pages written in HTML.
The worm then uses those e-mail addresses to target other users,
sending out a flood of messages using a built-in SMTP (Simple Mail
Transfer Protocol) engine. It is also able to spread to other
computers on a network using shared folders and the copies itself
to the shared folder file on the KaZaa peer-to-peer network using a
variety of file names, including Shrek_2.exe.
Antivirus companies recommended that Windows users who have not
done so already apply software patches for the LSASS and DCOM and
update their antivirus software to spot Plexus.
Paul Roberts writes for IDG News
Service