The CERT_CONTEXT Structure Variable Is Not Available for Web Filters in ISA (319375)


The information in this article applies to:

  • Microsoft Internet Security and Acceleration Server 2000
  • Microsoft Internet Security and Acceleration Server 2000 SP1
This article was previously published under Q319375

SYMPTOMS

When you try to write a Web filter for Internet Security and Acceleration (ISA) Server that does client certificate Certificate Revocation List (CRL) validation, you cannot use the CertVerifyRevocation application programming interface (API) because no CERT_CONTEXT structure server variable is available.

CAUSE

Because ISA Server does not fully expose a pointer to the CERT_CONTEXT structure, it cannot be used from a Web filter to perform actions such as CRL checking.

RESOLUTION

You must install ISA Server Service Pack 1 (SP1) before you apply the following hotfix.

For additional information about how to obtain the latest ISA Server service pack, click the article number below to view the article in the Microsoft Knowledge Base:

313139 How to Obtain the Latest Internet Security and Acceleration Server

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

To install the fix, run the self-extracting file. You do not have to restart the ISA Server computer. If the computer is part of an ISA Server array, you do not have to shut the whole array down; you can still install this fix on a one-by-one basis.

The English version of this fix should have the following file attributes or later:
   Date          Time   Version       Size     File name
   -------------------------------------------------------
   11-June-2002  18:38  3.0.1200.178  386,832  W3proxy.exe
This fix also applies to the French, German, Spanish, and Japanese versions of ISA Server.


STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

MORE INFORMATION

This hotfix makes the CERT_CONTEXT structure server variable available in the HTTP_FILTER_AUTH_COMPLETE_INFO Web filter notification. The CERT_CONTEXT structure is not available in any other notifications. Note that Web filters receive a const pointer to the CERT_CONTEXT structure. You do not have to free the memory that is used by the structure because the Web proxy automatically cleans it up at the end of each request.

The following code can be used to get CERT_CONTEXT structure: 
PCERT_CONTEXTpCertCntxt;
DWORDdwCertSize = sizeof(PCERT_CONTEXT);
pfc->GetServerVariable(
pfc,
"CERT_CONTEXT",
&pCertCntxt,
&dwCertSize);
ISA does not do client certificate CRL checking in a Web publishing scenario when Secure Sockets Layer (SSL) is used and when client certificates are used as the authentication method. To use CRL checking, you must both use a Web filter and install this hotfix.

When the certificate is validated against the CRL, it may generate a network request. You can make any networking call from a web filter. However, a static packet filter must be created for the traffic if the target of the request is behind the external network adapter and packet filtering is turned on. This filter can be created exactly to the target you need so this does not introduce a security hole.

For more information about writing Web filters, visit the following Microsoft Web site:

ISA Server SDK Documentation
http://www.microsoft.com/isaserver/techinfo/productdoc/2000/SDKdownload.asp

Modification Type:MinorLast Reviewed:10/11/2005
Keywords:kbHotfixServer kbQFE kbbug kbfix kbQFE KB319375
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