If you haven't patched the Windows Server Service vulnerability fixed by Microsoft last month, it's time to make it a priority.
Though Microsoft issued a rare out-of-band patch for the issue in October, a number of exploits taking advantage of the vulnerability continue to be a problem. This past weekend, Microsoft began receiving customer reports regarding increased malware attacks targeting the flaw. The attacks continued to gain momentum as the days went on, prompting Microsoft to post an advisory on its Security Response Center blog.
The vulnerability attackers are targeting is due to the Windows Server Service improperly handling remote protocol (RPC) requests. With a specially-crafted RPC, an attacker can take advantage of the security gap to take over a system.
The latest malware is detected by Microsoft as Win32/Conficker.A, W32/Conficker by McAfee and W32.Downadup by Symantec.
"Once loaded in the service space, the worm attempts to download files from the Internet-specifically, further malware from trafficconverter.biz and data files from maxmind.com," wrote Alex Hinchliffe, a researcher with McAfee's Avert Labs, in a recent post on the lab's blog. "The worm continues by setting up an HTTP server that listens on a random port on the victim's system while hosting a copy of the worm. It then scans for new vulnerable victims to exploit, at which point the new victim will download the worm from the previous victim and so on."
On the Microsoft's Malware Protection Center (MPC) blog, it was noted that the worm mostly spreads within corporations, but has also infected several hundred home users. Most of the reports of infections are coming from users in the United States, but there are also reports from Germany, Spain, France and other countries.
Strangely, the worm patches the vulnerable API in memory - a move that may be an attempt by attackers to prevent other malware from taking over the computer as well.
The issue can be exploited without authentication on Windows 2000, XP and Server 2003 platforms. Windows Vista and Windows Server 2008 are also affected, but the vulnerable code path is only accessible to authenticated users.
As a workaround, enterprises can disable the computer browser service. Directions on how to do this are included in the Microsoft advisory. Windows Vista and Windows Server 2008 users can also filter the affected RPC identifier.