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AUSCERT External Security Bulletin Redistribution
ESB-2013.1782
Changes in Windows Authenticode Signature Verification
11 December 2013
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AusCERT Security Bulletin Summary
---------------------------------
Product: Microsoft Windows
Publisher: Microsoft
Operating System: Windows
Impact/Access: Reduced Security -- Unknown/Unspecified
Resolution: Patch/Upgrade
Original Bulletin:
http://technet.microsoft.com/en-us/security/advisory/2915720
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Microsoft Security Advisory (2915720)
Changes in Windows Authenticode Signature Verification
Published: Tuesday, December 10, 2013
Version: 1.0
General Information
Executive Summary
Microsoft is announcing the availability of an update for all supported
releases of Windows to change how signatures are verified for binaries signed
with the Windows Authenticode signature format. The change is included with
Security Bulletin MS13-098, but will not be enabled until June 10, 2014. Once
enabled, the new default behavior for Windows Authenticode signature
verification will no longer allow extraneous information in the
WIN_CERTIFICATE structure. Note that after June 10, 2014, Windows will no
longer recognize non-compliant binaries as signed.
Recommendation. Microsoft recommends that by June 10, 2014, executables
authors ensure that all signed binaries comport with this new verification
behavior by containing no extraneous information in the WIN_CERTIFICATE
structure. Microsoft also recommends that customers appropriately test this
change to evaluate how it will behave in their environments. Please see the
Suggested Actions section of this advisory for more information.
Suggested Actions
Review Microsoft Root Certificate Program Technical Requirements
Customers who are interested in learning more about the topic covered in this
advisory should review Windows Root Certificate Program - Technical
Requirements.
Modify Binary Signing Processes by June 10, 2014
After reviewing the technical details underlying the change in Authenticode
signature verification behavior, Microsoft recommends that customers ensure
that their Authenticode signatures do not contain extraneous information in
the WIN_CERTIFICATE structure. Microsoft also recommends that executables
authors verify that their Authenticode-signed binaries conform to the new
verification requirements before June 10, 2014. Authors who have modified
their binary signing processes and would like to enable the new behavior prior
to June 10, 2014 may do so on an opt-in basis. After June 10, 2014, binaries
with signatures that do not conform to the new verification process will be
considered unsigned. See Windows Root Certificate Program - Technical
Requirements for guidance.
Test the Improvement to Authenticode Signature Verification
Microsoft recommends that customers test how this change to Authenticode
signature verification behaves in their environment by enabling it prior to
June 10, 2014. To enable the Authenticode signature verification improvements,
create (or modify) the system registry key and string value detailed below and
set the string value to "1" (setting the string value to "0", or deleting the
key, effectively disables the update):
Warning If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.
To enable the update:
HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\Wintrust\Config
EnableCertPaddingCheck = "1"
To disable the update:
HKEY_LOCAL_MACHINE\Software\Microsoft\Cryptography\Wintrust\Config
EnableCertPaddingCheck = "0"
Note Enabling the update will cause non-conforming binaries to appear unsigned
and, therefore, render them untrusted.
Keep Windows Updated
Windows users should apply the latest Microsoft security updates to help make
sure that their computers are as protected as possible. If you are not sure
whether your software is up to date, visit Windows Update, scan your computer
for available updates, and install any high-priority updates that are offered
to you. If you have Automatic Updates enabled, the updates are delivered to
you when they are released, but you have to make sure you install them.
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