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                           CERT-Renater

               Note d'Information No. 2015/VULN081
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DATE                : 13/05/2015

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Windows version Vista, Server 2008, 7, 8, 8.1, RT,
                      RT 8.1, Server 2012, Server 2003
                     running Schannel.

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KB3061518
https://technet.microsoft.com/en-us/library/security/MS15-055
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MS15-055: Vulnerability in Schannel Could Allow Information Disclosure
(3061518) - Important

Bulletin Number: MS15-055

Bulletin Title: Vulnerability in Schannel Could Allow Information Disclosure

Severity: Important

KB Article: 3061518

Version: 1.0

Published Date: May 12, 2015

Executive Summary

This security update resolves a vulnerability in Microsoft Windows. The
vulnerability could allow information disclosure when Secure Channel
(Schannel) allows the use of a weak Diffie-Hellman ephemeral (DFE) key
length of 512 bits in an encrypted TLS session. Allowing 512-bit DHE
keys makes DHE key exchanges weak and vulnerable to various attacks. A
server needs to support 512-bit DHE key lengths for an attack to be
successful; the minimum allowable DHE key length in default
configurations of Windows servers is 1024 bits.

This security update is rated Important for all supported releases of
Microsoft Windows. For more information, see the Affected Software section.


Affected Software

Windows Server 2003 Service Pack 2

Windows Server 2003 x64 Edition Service Pack 2

Windows Server 2003 with SP2 for Itanium-based Systems

Windows Vista Service Pack 2

Windows Vista x64 Edition Service Pack 2

Windows Server 2008 for 32-bit Systems Service Pack 2

Windows Server 2008 for x64-based Systems Service Pack 2

Windows Server 2008 for Itanium-based Systems Service Pack 2

Windows 7 for 32-bit Systems Service Pack 1

Windows 7 for x64-based Systems Service Pack 1

Windows Server 2008 R2 for x64-based Systems Service Pack 1

Windows Server 2008 R2 for Itanium-based Systems Service Pack 1

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[1]

Windows RT 8.1[1]

Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core
installation)

Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core
installation)

Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core
installation)

Windows Server 2012 (Server Core installation)

Windows Server 2012 R2 (Server Core installation)

[1]This update is available via Windows Update only.


Vulnerability Information

Schannel Information Disclosure Vulnerability - CVE-2015-1716

An information disclosure vulnerability exists in Secure Channel
(Schannel) when it allows the use of a weak Diffie-Hellman ephemeral
(DFE) key length of 512 bits in an encrypted TLS session. Allowing
512-bit DHE keys makes DHE key exchanges weak and vulnerable to various
attacks.

The security update addresses the vulnerability by increasing the
minimum allowable DHE key length to 1024 bits.

Microsoft received information about this vulnerability through
coordinated vulnerability disclosure. When this security bulletin was
issued, Microsoft had not received any information to indicate that
this vulnerability had been publicly used to attack customers.

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