Plexus worm targets Microsoft vulnerabilities

Antivirus software companies have warned of an e-mail worm that targets unpatched Microsoft Windows machines with either of two recently disclosed software vulnerabilities.

Download this free guide

From forensic cyber to encryption: InfoSec17

Security technologist Bruce Schneier’s insights and warnings around the regulation of IoT security and forensic cyber psychologist Mary Aiken’s comments around the tensions between encryption and state security were the top highlights of the keynote presentations at Infosecurity Europe 2017 in London.

Start Download

• Corporate E-mail Address:

  You forgot to provide an Email Address.

  This email address doesn’t appear to be valid.

  This email address is already registered. Please login.

  You have exceeded the maximum character limit.

  Please provide a Corporate E-mail Address.

By submitting my Email address I confirm that I have read and accepted the Terms of Use and Declaration of Consent.

By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.

You also agree that your personal information may be transferred and processed in the United States, and that you have read and agree to the Terms of Use and the Privacy Policy.

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