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Microsoft Reports Critical Vulnerability in Windows 2000, XP

Microsoft Corp. reported a critical vulnerability in Windows 2000 and Windows XP on Thursday. The flaw results from an unchecked buffer in Microsoft's Point-to-Point Tunneling Protocol (PPTP) implementation in the two operating systems. An attacker could exploit the flaw to mount a denial of service attack.

The bulletin was one of three security bulletins released by Microsoft's security team on Thursday morning. The other newly patched vulnerabilities involve Internet Information Server and Windows 2000.

PPTP is a Virtual Private Networking technology natively supported in Windows 2000 and Windows XP. According to the bulletin, the unchecked buffer exists in a section of code that processes the control data used to establish, maintain and tear down PPTP connections.

An attacker would exploit the flaw by sending specially malformed PPTP control data to a server or workstation acting as a server. The attack could corrupt kernel memory and cause the system to fail. Rebooting restores normal operation. PPTP is not enabled by default on any Windows system so servers have to be configured to offer PPTP services to be vulnerable.

In a separate bulletin, four less serious vulnerabilities in IIS got patches. The most serious of the vulnerabilities makes it possible for applications on a server to gain system-level privileges. The patch for the flaws is cumulative, including all IIS-related fixes since Windows NT 4.0 Service Pack 6a.

The other security vulnerability, rated "moderate," by Microsoft is that default permissions in Windows 2000 could allow a Trojan horse program. Microsoft says the systems most at risk from this vulnerability is a workstation shared by several users. The attacker would need to be able to log on locally to load the Trojan horse.

So far this year, Microsoft has distributed 64 security bulletins for its products.

Click here to view Microsoft's new security bulletins:

  • Cumulative patch for IIS vulnerabilities,
  • Critical PPTP implementation flaw,
  • Trojan horse program execution.

    • About the Author

    Scott Bekker is editor in chief of Redmond Channel Partner magazine.

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