A series of new variants of the prolific Bagle worm has raised alarms in the security community through an innovative infection mechanism: The e-mail message in which the variants arrive may have no file attachment, and its possible for a user to become infected without having to launch one.
The message includes a Windows ActiveX control and uses a vulnerability announced and patched by Microsoft Corp. in August and another problem from last October. The most recent Cumulative Security Update for Internet Explorer also includes a fix for the more recently discovered flaw.
The ActiveX control does not contain the actual worm, according to McAfee Security. Instead, it creates and runs a VBScript on the system, which downloads and executes the worm from one of a list of IP addresses. According to McAfee, as of 06:45 PST on March 18, “The majority of the 590 IP addresses seen have been closed down. At the time of writing, 39 were still responding.”
Antivirus companies have become out of sync with each other with respect to Bagle variants. Panda Software refers to the new ones as Bagle.P, Bagle.Q and Bagle.R., with Bagle.Q as the most serious one. Panda reports that the worm “infects PE files [which are standard Windows .EXE programs], downloads a file from the Internet and ends processes belonging to security applications.” Kaspersky Labs Int.s analysis of the code says that the program attempts to infect PE files but fails to do so due to an error in the code.
According to Trend Micro Inc.s analysis of the worm, it also spreads through the conventional e-mail attachment mechanism, as well as through peer-to-peer networks and shared folders. Symantec Corp. calls the three worms Beagle.R, Beagle.S and Beagle.T but did not have analysis ready for them as of this storys posting.
The ActiveX infection mechanism requires that the e-mail client permit ActiveX controls to run in HTML e-mail. Microsoft e-mail clients have disallowed this feature by default for several years.
All of the major antivirus companies claim to have detection definitions available for the worms. However, they havent necessarily prepared disinfection routines.