Microsoft Security Bulletin MS99-053 - Critical
Patch Available for "Windows Multithreaded SSL ISAPI Filter" Vulnerability
Published: December 02, 1999
Originally Posted: December 02, 1999
Microsoft has released a patch that eliminates a vulnerability in the SSL ISAPI filter that ships with Microsoft® Internet Information Server and is used by other Microsoft products. If called by a multi-threaded application under very specific, and fairly rare, circumstances, a synchronization error in the filter could allow a single buffer of plaintext to be transmitted back to the data's owner.
Frequently asked questions regarding this vulnerability can be found at http://www.microsoft.com/technet/security/bulletin/fq99-053.mspx.
The SSL ISAPI filter provided as part of IIS supports concurrent use. When used in this mode, a synchronization problem could induce a race condition and cause a single buffer of plaintext to be leaked. The conditions under which this could happen are very rare, and could only occur when a single user's session was multi-threaded and traffic volumes were extremely high.
The scope of this vulnerability is very limited. The leaked plaintext would always be sent to its owner, never another user. Also, because the leaked data would fail its integrity check, the effect of the leak would be to cause the SSL session to immediately collapse. The condition could not be induced by a hostile user, and would offer at best a target of opportunity. Finally, it is worth noting that this vulnerability only affects the SSL ISAPI filter, not the secure communications capability provided by Windows NT via Schannel.
Affected Software Versions
- Microsoft IIS 4.0
- Microsoft Site Server 3.0
- Microsoft Site Server Commerce Edition 3.0
Vulnerability Identifier: CVE-1999-0861
NOTE: This and other patches are available from the Microsoft Download Center
Please see the following references for more information related to this issue.
- Microsoft Security Bulletin MS99-053: Frequently Asked Questions, http://www.microsoft.com/technet/security/bulletin/fq99-053.mspx.
- Microsoft Knowledge Base (KB) article 244613, IIS 4.0 SSL ISAPI Filter Can Leak Single Buffer of Plaintext, http://support.microsoft.com/default.aspx?scid=kb;en-us;244613&sd=tech.
(Note: It may take 24 hours from the original posting of this bulletin for this KB article to be visible.)
- Microsoft Security web site, http://www.microsoft.com/technet/security/default.mspx.
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/contactussupport/?ws=support.
Microsoft acknowledges Wall Data for bringing this issue to our attention.
- December 02, 1999: Bulletin Created.
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