SYMPTOMS
Microsoft has released a patch that eliminates a security vulnerability in Internet Information Server (IIS) 4.0 and Internet Information Services (IIS) 5.0. Under very unusual conditions, this vulnerability can allow an attacker to read fragments of files from a Web server.
This vulnerability involves a new variant of the "File Fragment Reading via .HTR" vulnerability, which is described in
Microsoft Security Bulletin (MS00-044). Like the other variants, this one may allow an attacker to request a file in a way that causes it to be processed by the .htr ISAPI extension. The result of this is that fragments of server-side files such as .asp files may potentially be sent to the attacker. There is no capability through this vulnerability to add, change, or delete files on the server, or to access a file without permissions.
There are a number of significant restrictions on this vulnerability:
- During normal .htr processing, the effect is to strip out the very data that would be the most likely to contain sensitive information.
- There must be zeros fortuitously located in the server memory in order for the file fragments to be sent.
- If best practices have been followed regarding the need to avoid ever storing sensitive information in .asp and other server-side files, there should be no sensitive information in the files to begin with.
Customers who have previously disabled the .htr functionality are not affected by this vulnerability. Microsoft recommends that all customers disable .htr functionality, unless there is a business-critical reason for keeping it. For the latter group of customers, a patch is available that eliminates this vulnerability.
RESOLUTION
Internet Information Services 5.0
To resolve this problem, either obtain the hotfix referenced in this section or 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:
311401 Windows 2000 Security Rollup Package 1 (SRP1), January 2002
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
The following files are available for download from the Microsoft
Download Center:
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591 How to Obtain Microsoft Support Files from Online Services
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:
Date Time Version Size File name Platform
-----------------------------------------------------------------
5/31/2001 03:31p 5.0.2195.3649 46,352 Ism.dll x86
NOTE: Due to file dependencies, this hotfix requires Microsoft Windows NT 4.0 Service Pack 5 or Service Pack 6a.
Internet Information Server 4.0
Windows NT 4.0
To resolve this problem, obtain the Windows NT 4.0 Security Rollup Package.
For additional information, click the article number below
to view the article in the Microsoft Knowledge Base:
299444 Post-Windows NT 4.0 Service Pack 6a Security Rollup Package (SRP)
Microsoft Windows NT Server version 4.0, Terminal Server Edition
To resolve this problem, obtain the Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package
(SRP). For additional information about the SRP, click the article number below
to view the article in the Microsoft Knowledge Base:
317636 Windows NT Server 4.0, Terminal Server Edition, Security Rollup Package
