A security company said Tuesday that it found an example of working computer source code that exploits the latest critical security hole disclosed by Microsoft.
Counterpane Internet Security Inc., of Cupertino, California, said that it found and tested the source code, which it claims exploits Microsoft Windows systems that have one of three security flaws in the Microsoft Distributed Component Object Model (DCOM) component of Windows.
The development of a working exploit is a crucial step toward the creation of an Internet worm or virus that can infect large numbers of vulnerable Windows systems, raising the stakes for companies and home users who have not downloaded and installed the Microsoft-supplied software patch, according to Bruce Schneier, CTO of Counterpane.
Microsoft last week revealed the new DCOM security holes in a bulletin, MS03-039. The company said the holes are very similar to an earlier DCOM vulnerability that was exploited by the W32.Blaster and W32.Welchia Internet worms in August.
Malicious hackers could exploit the latest vulnerability by creating a program to send improperly formatted RPC (Remote Procedure Call) messages to a vulnerable machine. Those messages could cause a buffer overflow that would enable attackers to place and run their own computer code on the machine, without requiring the machine's owner to open an e-mail attachment or perform any other action, Microsoft said. (Microsoft's security bulletin can be found at http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-039.asp.)
Counterpane tested the exploit code in its labs and found that the code opens an interface on the vulnerable system that would enable remote attackers to issue commands and take control of the system, according to Schneier.
This is the first known exploit of one of the vulnerabilities from the MS03-039 bulletin, Schneier said.
Counterpane researchers found the code on a public Web site frequented by virus writers but do not believe it has been released to the public yet, he said.
No Counterpane customers have been attacked, he said.
The exploit could easily be used in a worm, or even swapped into the existing Blaster worm in place of the previous DCOM exploit code, Schneier said.
The appearance of exploit code means that companies should rush to patch vulnerable Windows machines while plugging ports targeted by the exploit, such as 135, 139 and 445.
"Last week the news was, 'It's coming, gotta get to (patching) quickly.' Now the news is 'It's here. We've seen it. We have it. You've gotta get to (patching) now,'" Schneier said.
Because the exploit would be stopped by typical corporate firewall defenses, companies should pay particular attention to employees who bring laptops home with them or take them on the road for travel. Often those users get infected when not connected to the corporate network, then spread the infection to other machines on the network when they return to work, he said.