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AUSCERT External Security Bulletin Redistribution
ESB-2015.1290
MS15-055: Vulnerability in Schannel Could Allow Information
Disclosure (3061518) - Important
13 May 2015
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AusCERT Security Bulletin Summary
---------------------------------
Product: Microsoft Windows
Publisher: Microsoft
Operating System: Windows
Impact/Access: Reduced Security -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2015-1716
Original Bulletin:
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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