A security company claims to have found an example of working computer source code that exploits the latest critical security hole disclosed by Microsoft.
Counterpane Internet Security said that it found and tested the source code, which it claimed 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 were 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 Remote Procedure Call (RPC) 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 email attachment or perform any other action, Microsoft said.
Counterpane tested the exploit code in its labs and found that the code opened an interface on the vulnerable system that would enable remote attackers to issue commands and take control of the system, Schneier said.
This was the first known exploit of one of the vulnerabilities from the MS03-039 bulletin, he said.
Counterpane researchers found the code on a public Web site frequented by virus writers but did not believe it had been released to the public yet, Schneier said.
No Counterpane customers had 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 became infected when not connected to the corporate network, then spread the infection to other machines on the network when they returned to work, he said.