Microsoft Plugs Code Execution Holes on Patch Day

The December batch of updates from Microsoft includes a fix for a previously reported WINS server flaw; Microsoft explains why some code execution flaws aren't rated "critical."

Microsoft on Tuesday released fixes for five vulnerabilities in Windows products, including a patch for a known security issue in the WINS (Windows Internet Name Service) name server.

As expected, the company released five advisories with "important" severity ratings but warned that four of the five could lead to code execution attacks.

Microsoft typically rates code execution flaws as "critical," and the lowered ratings raised some eyebrows since independent researchers have already warned of the serious nature of the WINS vulnerability, which could allow a remote attacker to take complete control of an affected system.

According to Stephen Toulouse, program manager at the Microsoft Security Response Center, "critical" ratings are reserved for bugs that the company considers "wormable."

"A critical vulnerability means that, in the default scenario on a PC connected to the Internet, a criminal could exploit it in such a way that it spreads from machine to machine. We reserve critical ratings for vulnerabilities that are wormable," Toulouse told

"Code execution does not necessarily mean its critical," he said, explaining that the WINS vulnerability was rated one step below because it was not an Internet-facing technology and because the service is not installed by default on Windows systems.

The WINS patch (MS04-045) comes just two weeks after a private research firm warned that it could lead to complete system hijack. Microsoft confirmed as much in its December advisory.

"An attacker who successfully exploited the most severe of these vulnerabilities could take complete control of an affected system, including installing programs; viewing, changing or deleting data; or creating new accounts that have full privileges," the company said.

The company said WINS users were at risk of system hijack because of the way the WINS server handles computer name validation and association context validation. A hacker could exploit the name validation flaw by constructing a malicious network packet that could potentially allow remote code execution on an affected system.

According to the alert, the association context vulnerability could allow an attacker to construct a malicious network packet to take complete control of an affected system. In Windows Server 2003, the company said an exploit would only result in a denial-of-service condition.

Microsoft already released bulletin MS04-041 to plug two holes in WordPad that put users at risk of code execution attacks. Affected software include Windows NT Server 4.0, Windows 2000, Windows XP Service Pack 1 and Windows Server 2003.

The WordPad flaws exist in the table conversion and font conversion features. While a successful attack could lead to harmful code execution, Microsoft said significant user interaction is required to exploit both vulnerabilities.

Next Page: Patch No. 3 fixes bugs in the DHCP Server service.