[ISN] Microsoft Plugs Code Execution Holes on Patch Day

[InfoSec News]

http://www.eweek.com/article2/0,1759,1741024,00.asp

By Ryan Naraine 
December 14, 2004 

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 eWEEK.com.

"Code execution does not necessarily mean it's 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.

A third patch, MS04-042, corrects two bugs in the DHCP (Dynamic Host
Configuration Protocol) Server service that could allow code execution
and denial-of-service attacks. The DHCP flaw affects Windows NT Server
4.0 customers.

Microsoft warned that a successful exploit of the DHCP holes could
allow an attacker to take complete control of an affected system,
including installing programs; viewing, changing, or deleting data; or
creating new accounts that have full privileges.

A separate advisory, MS04-043, was released to stop a buffer overrun
found in the Windows HyperTerminal utility. Affected software includes
Windows NT Server 4.0, Windows 2000, Windows XP (SP1 and SP2) and
Windows Server 2003.

The company warned that an attacker could construct a malicious
HyperTerminal session file to launch code on a vulnerable system.  
"This vulnerability could attempt to be exploited through a malicious
Telnet URL if HyperTerminal has been set as the default Telnet client.  
An attacker who successfully exploited this vulnerability could take
complete control of an affected system," according to the advisory.

The fifth "important" advisory for December, MS04-044, corrects issues
in Windows Kernel and LSASS that could allow privilege elevation
attacks. Microsoft said a successful exploit could put users at risk
of having programs installed or data viewed, deleted or changed.

The company also reissued the MS04-028 advisory, which affected JPEG
Parsing (GDI+) in Windows, Office, Graphics Application and Developer
Applications subsystem in Microsoft Windows.

The reissue addresses newly available updates for Microsoft Visual
FoxPro 8.0 and the Windows .Net Framework 1.0 and 1.1 without Service
Pack 1.

Two of the five December bulletins apply to Windows XP Service Pack 2,
but the severity rating is reduced to "moderate" for those customers.