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Cache Expiration Does Not Free All Memory Associated with Expired Credentials

This article was previously published under Q316683
This article has been archived. It is offered "as is" and will no longer be updated.
Programs that use cryptographic functions that are provided by Schannel.dll may show a memory leak. A function that is typically used at the beginning of the sequence might be the AcquireCredentialsHandle function. Programs that make many Secure Sockets Layer (SSL) connections rapidly may experience this leak. For example, Microsoft Exchange 5.5 Service Pack 4 (SP4) experiences this leak.
The problem is caused by the caching mechanism in Schannel.dll. Typically, credentials are cached for a while in case a client wants to try a reconnection. Reconnections are effectively a mini-SSL handshake, during which the client uses the session keys from a previous session.

This behavior occurs when you access Exchange over IMAP4 SSL port 993. Using IMAP4 port 143, which is not an SSL port, does not show the leak.
A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem.

To resolve this problem, 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: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 usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this fix should have the following file attributes or later:
   Date         Time   Version         Size     File name   --------------------------------------------------------   09-Jul-2002  20:29  4.87.1964.1878  112,912  Sch128c.dll   09-Jul-2002  20:29  4.86.1964.1878  143,632  Schnlc.dll				
NOTE: Because of file dependencies, this hotfix requires Microsoft Windows NT 4.0 Service Pack 6a.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

Article ID: 316683 - Last Review: 10/24/2013 09:29:38 - Revision: 1.3

Microsoft Windows NT Server 4.0 Standard Edition, Microsoft Windows NT 4.0 Service Pack 6a, Microsoft Windows NT Server 4.0 Enterprise Edition, Microsoft Windows NT 4.0 Service Pack 6a

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