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AUSCERT External Security Bulletin Redistribution
ESB-2015.0982
Microsoft Security Bulletin MS15-041 - Important
15 April 2015
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AusCERT Security Bulletin Summary
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Product: Microsoft .NET Framework
Publisher: Microsoft
Operating System: Windows
Impact/Access: Access Confidential Data -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2015-1648
Original Bulletin:
https://technet.microsoft.com/en-us/library/security/MS15-041
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Microsoft Security Bulletin MS15-041 - Important
Vulnerability in .NET Framework Could Allow Information Disclosure (3048010)
Published: April 14, 2015
Version: 1.0
Executive Summary
This security update resolves a vulnerability in Microsoft .NET Framework. The
vulnerability could allow information disclosure if an attacker sends a
specially crafted web request to an affected server that has custom error
messages disabled. An attacker who successfully exploited the vulnerability
would be able to view parts of a web configuration file, which could expose
sensitive information.
This security update is rated Important for Microsoft .NET Framework 1.1
Service Pack 1, Microsoft .NET Framework 2.0 Service Pack 2, Microsoft .NET
Framework 3.5, Microsoft .NET Framework 3.5.1, Microsoft .NET Framework 4,
Microsoft .NET Framework 4.5, Microsoft .NET Framework 4.5.1, and Microsoft
.NET Framework 4.5.2 on affected releases of Microsoft Windows. For more
information, see the Affected Software section.
Affected Software
Windows Server 2003
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
Windows Vista Service Pack 2
Windows Vista x64 Edition Service Pack 2
Windows Server 2008
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
Windows 7 for 32-bit Systems Service Pack 1
Windows 7 for x64-based Systems Service Pack 1
Windows Server 2008 R2
Windows Server 2008 R2 for x64-based Systems Service Pack 1
Windows Server 2008 R2 for Itanium-based Systems Service Pack 1
Windows 8 and Windows 8.1
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 and Windows Server 2012 R2
Windows Server 2012
Windows Server 2012 R2
Windows RT and Windows RT 8.1
Windows RT
Windows RT 8.1
Server Core installation option
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)
Vulnerability Information
ASP.NET Information Disclosure Vulnerability - CVE-2015-1648
An information disclosure vulnerability exists in ASP.NET that is caused when
ASP.NET improperly handles certain requests on systems that have custom error
messages disabled. An attacker who successfully exploited the vulnerability
would be able to view parts of a web configuration file, which could expose
sensitive information.
To exploit this vulnerability, an attacker could a send a specially crafted
web request to an affected server with the intention of eliciting an error
message that could disclose information pertaining to the source line that
originated the exception. Ultimately, this could disclose information that was
not intended to be accessible. The security update addresses the vulnerability
by removing file content details from the error messages that were
facilitating the information disclosure.
By default, ASP.NET applications are not exposed to this vulnerability because
they are configured to not display detailed error messages to remote users.
Sometimes developers turn on detailed error messages to gather information and
then fail to turn them off, which would then expose the application to this
vulnerability.
The default setting in web.config is as follows:
<customErrors mode="remoteOnly" />
In a production environment, best practice would see this entry changed to the
following:
<customErrors mode="On" defaultRedirect="ErrorPage.htm" />
As a general rule, in production environments developers should never use the
following:
<customErrors mode="off" />
Note that error messages are customizable based on the error code. For more
information, see customErrors Element (ASP.NET Settings Schema).
As an added protection against accidental disabling of custom errors, machine
administrations can turn on retail mode. See the related workaround in this
bulletin for more information.
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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