Just weeks after weeks after the appearance of the Blaster worm, the company released software patches to close security holes similar to those Blaster exploited.
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All of Microsoft's supported operating systems are affected, except for Windows ME (Millennium Edition).
The vulnerabilities could be used by a remote attacker to take control of vulnerable systems, installing programs or changing data stored on a hard drive, Microsoft said on Wednesday.
The three security vulnerabilities affect the DCOM (Distributed Component Object Model) interface to a Windows component called the RPCSS service. That service processes messages using the RPC (Remote Procedure Call) protocol, according to Microsoft security bulletin MS03-039.
Malicious hackers could exploit the vulnerability by creating a program to send improperly formatted RPC messages to the RPCSS service on 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, Microsoft said.
The security holes are "very similar" to a vulnerability disclosed in July, according to Jeff Jones, senior director of Trustworthy Computing security at Microsoft.
Code to exploit that vulnerability appeared on the internet shortly after the release of the MS03-026 security bulletin. Within weeks, an worm using that exploit code, W32.Blaster, was released, infecting hundreds of thousands of computers worldwide
The patch released yesterday also covers the earlier RPC hole and supersedes that earlier patch. Microsoft now recommends customers apply MS03-039 instead of the MS03-026 patch, Jones said.
To prevent a similar occurrence with the new RPC vulnerabilities, Microsoft is encouraging customers to use firewall software to block access to unnecessary communications ports such as those used by Blaster.
For enterprise customers and others who need technical information about the new vulnerabilities, Microsoft released an updated network scanning tool which can identify vulnerable Windows systems. The company will also host a webcast on Friday.
The vulnerabilities were discovered internally, as well as by independent security companies, including eEye Digital Security. The new findings are the result of increased scrutiny of Windows code used to handle RPC since the discovery of the earlier RPC DCOM vulnerability by the Polish hacking group, the Last Stage of Delirium Research Group.
Jones said Microsoft was unaware of any attacks using the vulnerabilities.
He declined to comment on whether existing versions of the Blaster worm might be modified to exploit the new vulnerabilities.
"I don't want to speculate about different ways that people might try to exploit these vulnerabilities," he said.
Paul Roberts writes for IDG News Service