MS01-033: Unchecked Buffer in Index Server ISAPI Extension Can Enable Web Server Compromise

As part of its installation process, IIS installs several ISAPI extensions. These are dynamic-link libraries (DLLs) that provide extended functionality. Among these is Idq.dll, which is a component of Index Server (known in Windows 2000 as Indexing Service) that provides support for administrative scripts (these are Internet Data Administration, or .ida, files) and Internet Data Query (.idq) files.

A security vulnerability results because Idq.dll contains an unchecked buffer in a section of code that handles input URLs. An attacker who can establish a Web session with a server on which Idq.dll is installed can conduct a buffer overrun attack and execute code on the Web server. Idq.dll runs in the System context, so exploiting the vulnerability gives the attacker complete control of the server and allows him to take any desired action on it.

The buffer overrun occurs before any indexing functionality is requested. As a result, even though Idq.dll is a component of Index Server/Indexing Service, the service does not need to be running for an attacker to exploit the vulnerability. As long as the script mapping for .idq or .ida files is present, and the attacker is able to establish a Web session, he can exploit the vulnerability.

Clearly, this is a serious vulnerability, and Microsoft urges all customers to take action immediately. Customers who cannot install the patch can protect their systems by removing the script mappings for .idq and .ida files by using the Internet Services Manager in IIS. However, it is possible for these mappings to be automatically reinstated if additional system components are added or removed. Because of this, Microsoft recommends that all customers using IIS install the patch, even if the script mappings have been removed. For more information, see the FAQ portion of the following Microsoft Web site:

Mitigating Factors

• The vulnerability can only be exploited if a Web session can be established with an affected server. Customers who have installed Index Server or Index Services but not IIS are not at risk. This is the default case for Windows 2000 Professional.
• The vulnerability cannot be exploited if the script mappings for .ida and .idq files are not present. The procedure for removing the mappings is discussed in the IIS 4.0 and IIS 5.0 Security checklists; they can be automatically removed with either the High Security Template or the Windows 2000 Internet Server Security Tool. Customers should be aware, however, that subsequently adding or removing system components can cause the mapping to be reinstated, as discussed in the FAQ.
  
  For more information, see the following Microsoft Web sites:
  • IIS 4.0
    http://technet.microsoft.com/en-us/library/cc750570.aspx

    (http://technet.microsoft.com/en-us/library/cc750570.aspx)
  • IIS 5.0
    http://technet.microsoft.com/en-us/windowsserver/2000/bb735378.aspx

    (http://technet.microsoft.com/en-us/windowsserver/2000/bb735378.aspx)
  • Windows 2000 Internet Server Security Tool
    http://technet.microsoft.com/en-us/library/cc184906.aspx

    (http://technet.microsoft.com/en-us/library/cc184906.aspx)
• An attacker's ability to extend control from a compromised Web server to other computers depends heavily on the specific configuration of the network. Best practices recommend that the network architecture account for the inherent high risk that computers in an uncontrolled environment, like the Internet, face by minimizing overall exposure though measures such as demilitarized zones (DMZs), operating with minimal services and isolating contact with internal networks. Steps like this can limit overall exposure and impede an attacker's ability to broaden the scope of a possible compromise.

Windows 2000

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: The resolution for this problem is also available in Windows 2000 Security Rollup Package 1 (SRP1). For additional information about SRP1, click the article number below to view the article in the Microsoft Knowledge Base: The following files are available for download from the Microsoft Download Center:
Release Date: Monday, June 18, 2001

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. NOTE: Customers who apply this patch on Windows 2000-based computers that are running Windows Management Instrumentation (WMI) may also need to apply an additional hotfix. Although it is unrelated to this particular patch, a known issue can cause the WMI process (Winmgmt.exe) to stop responding (hang) and consume 100 percent of CPU resources and memory if a program queries for the Win32_QuickFixEngineering objects. For example, this can occur when Microsoft Systems Management Server (SMS) queries WMI to determine which hotfixes have been applied. For additional information about how to resolve this problem, click the article number below to view the article in the Microsoft Knowledge Base: The English version of this fix should have the following file attributes or later: NOTE: Due to file dependencies, this hotfix requires Microsoft Windows 2000 Service Pack 1 or later.

Windows NT 4.0 Server

To resolve this problem, obtain the individual package referenced below or obtain the Windows NT 4.0 Security Rollup Package. For additional information on the SRP, click the article number below to view the article in the Microsoft Knowledge Base: The following file is available for download from the Microsoft Download Center:
NOTE: Contact Product Support Services (PSS) for the Alpha version of this patch.

Release Date: Monday, June 18, 2001

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file. The English version of this fix should have the following file attributes or later: NOTE: Due to file dependencies, this hotfix requires Microsoft Windows NT 4.0 Service Pack 6a.

The original patched English version of this fix had the following file attributes: NOTE: The Idq.dll file has been re-released to correct a file version issue. Specifically, the Idq.dll version number in the original patch (dated May 25, 2001) was not incremented from that of the previous build (dated January 25, 2001). Instead, the version number for both was 5.0.1781.3. A new version of the patch was released on August 2, 2001, containing an Idq.dll file dated July 03, 2001, that was properly versioned with version number 5.0.1782.4. No other changes were made in the new version of the patch.

If you installed the original version of this patch (Idq.dll version 5.0.1781.3, dated May 25, 2001), you do not need to apply the new version (Idq.dll version 5.0.1782.4, dated July 03, 2001) because your system is already protected. However, if the version of the Idq.dll file on your computer is 5.0.1781.3, dated January 25, 2000, you should upgrade to the new version of the patch.

Windows NT Server 4.0, Terminal Server Edition

Index Server 2.0 is part of the Windows NT 4.0 Option Pack which is not supported on Windows NT Server 4.0, Terminal Server Edition. Patches for Index Server 2.0 have been provided as part of the Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package (SRP) only for customers who have installed the Option Pack to protect their computers during the migration to a supported operating system. For additional information about the SRP, click the article number below to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this problem may cause a degree of security vulnerability in Windows 2000 and Windows NT Server 4.0. This problem was first corrected in Windows 2000 Service Pack 3.

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: 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: