MS02-018: Patch Available for Chunked Encoding Transfer Mechanism Vulnerability (319688)

SYMPTOMS

A buffer overrun vulnerability exists in Internet Information Server (IIS) 4.0 and Internet Information Services (IIS) 5.0. By sending a specially chosen request to an affected web server, an attacker could either disrupt Web services or gain the ability to run a program on the server. Such a program would run with full system privileges in IIS 4.0, and with fewer but nevertheless significant privileges in IIS 5.0.

Customers who have used the IIS Lockdown Tool to configure their servers as static Web servers are already protected against this vulnerability. Likewise, the URLScan tool can be configured to block the vulnerability, and the affected mechanism itself can be disabled. However, because of the seriousness of the vulnerability, Microsoft recommends that all customers install the patch, including those who have already taken these steps.

CAUSE

This vulnerability results because of an arithmetic error in the Active Server Pages (ASP) functionality that enables data to be uploaded to a Web server by using chunked encoding. The error causes IIS to allocate a buffer of the wrong size to hold incoming data, with the result that the data could overrun the end of the buffer and neighboring system memory.

RESOLUTION

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Internet Information Services 5.0

The update for this problem is included in the "MS02-018: April 2002 Cumulative Patch for Internet Information Services". For additional information about how to obtain this patch, click the article number below to view the article in the Microsoft Knowledge Base:

319733 MS02-018: April 2002 Cumulative Patch for Internet Information Services

To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

260910 How to Obtain the Latest Windows 2000 Service Pack

Internet Information Server 4.0

319733 MS02-018: April 2002 Cumulative Patch for Internet Information Services

STATUS

Internet Information Services 5.0

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Microsoft Internet Information Services 5.0. This problem was first corrected in Windows 2000 Service Pack 3.

Internet Information Server 4.0

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Microsoft Internet Information Server 4.0.

MORE INFORMATION

The vulnerability that is described in this article does not apply to Internet Information Services (IIS) 5.1. However, a variant of this vulnerability that affects IIS 4.0, 5.0, and 5.1 exists elsewhere in the chunked-encoding mechanism. This variant could be exploited in a similar manner as the preceding vulnerability, and would have the same scope.

The update for these vulnerabilities is included in the "MS02-018: April 2002 Cumulative Patch for Internet Information Services". For additional information about how to obtain this patch, click the article number below to view the article in the Microsoft Knowledge Base:

319733 MS02-018: April 2002 Cumulative Patch for Internet Information Services

For more information about these vulnerabilities, see the following Microsoft Web site:

http://www.microsoft.com/technet/security/bulletin/MS02-018.mspx

For additional information about how to obtain a hotfix for Windows 2000 Datacenter Server, click the article number below to view the article in the Microsoft Knowledge Base:

265173 Datacenter Program and Windows 2000 Datacenter Server Product

For additional information about how to install multiple hotfixes with only one reboot, click the article number below to view the article in the Microsoft Knowledge Base:

296861 Use QChain.exe to Install Multiple Hotfixes with One Reboot