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AUSCERT External Security Bulletin Redistribution
Update to Improve TLS Session Resumption Interoperability
13 January 2016
AusCERT Security Bulletin Summary
Product: Microsoft Windows
Operating System: Windows
Impact/Access: Reduced Security -- Remote with User Interaction
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Microsoft Security Advisory 3109853
Update to Improve TLS Session Resumption Interoperability
Published: January 12, 2016
Microsoft is announcing the availability of an update to improve
interoperability between Schannel-based TLS clients and 3rd-party TLS servers
that enable RFC5077-based resumption and that send the NewSessionTicket
message in the abbreviated TLS handshake. The update addresses an issue in
schannel.dll that could cause RFC5077 session ticket-based resumption to fail
and subsequently cause WinInet-based clients (for example, Internet Explorer
and Microsoft Edge) to perform a fallback to a lower TLS protocol version than
the one that would have been negotiated otherwise. This improvement is part of
ongoing efforts to bolster the effectiveness of encryption in Windows.
For additional details and deployment guidance, see Microsoft Knowledge Base
Windows 8 for 32-bit Systems
Windows 8 for x64-based Systems
Windows 8.1 for 32-bit Systems
Windows 8.1 for x64-based Systems
Windows Server 2012
Windows Server 2012 R2
Windows RT 8.1
Windows 10 for 32-bit Systems
Windows 10 for x64-based Systems
Windows 10 Version 1511 for 32-bit Systems
Windows 10 Version 1511 for x64-based Systems
Server Core installation option
Windows Server 2012 (Server Core installation)
Windows Server 2012 R2 (Server Core installation)
What is the scope of the advisory?
To announce the availability of an update to improve interoperability between
Schannel-based TLS clients and 3rd-party TLS servers that enable RFC5077-based
resumption and that send the NewSessionTicket message in the abbreviated TLS
Is this a security issue?
No. This is a compliance issue regarding Schannel's implementation of RFC 5077
and is causing interoperability issues.
What does the update do?
The update addresses an issue in schannel.dll that could cause RFC5077 session
ticket-based resumption to fail and subsequently cause WinInet-based clients
(for example, Internet Explorer and Microsoft Edge) to perform a fallback to a
lower TLS protocol version than the one that would have been negotiated
Microsoft recognizes the efforts of those in the security community who help
us protect customers through coordinated vulnerability disclosure. See
Acknowledgments for more information.
Microsoft Active Protections Program (MAPP)
To improve security protections for customers, Microsoft provides
vulnerability information to major security software providers in advance of
each monthly security update release. Security software providers can then use
this vulnerability information to provide updated protections to customers via
their security software or devices, such as antivirus, network-based intrusion
detection systems, or host-based intrusion prevention systems. To determine
whether active protections are available from security software providers,
please visit the active protections websites provided by program partners,
listed in Microsoft Active Protections Program (MAPP) Partners.
You can provide feedback by completing the Microsoft Help and Support form,
Customer Service Contact Us.
Customers in the United States and Canada can receive technical support from
Security Support. For more information, see Microsoft Help and Support.
International customers can receive support from their local Microsoft
subsidiaries. For more information, see International Support.
Microsoft TechNet Security provides additional information about security in
The information provided in this advisory is provided "as is" without warranty
of any kind. Microsoft disclaims all warranties, either express or implied,
including the warranties of merchantability and fitness for a particular
purpose. In no event shall Microsoft Corporation or its suppliers be liable
for any damages whatsoever including direct, indirect, incidental,
consequential, loss of business profits or special damages, even if Microsoft
Corporation or its suppliers have been advised of the possibility of such
damages. Some states do not allow the exclusion or limitation of liability for
consequential or incidental damages so the foregoing limitation may not apply.
V1.0 (January 12, 2016): Advisory published.
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