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AUSCERT External Security Bulletin Redistribution
ESB-2010.0141
Vulnerability in TLS/SSL Could Allow Spoofing
11 February 2010
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AusCERT Security Bulletin Summary
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Product: Transport Layer Security (TLS)
Secure Sockets Layer (SSL)
Publisher: Microsoft
Operating System: Windows Server 2008
Windows Server 2003
Windows 2000
Windows 7
Windows Vista
Windows XP
Impact/Access: Provide Misleading Information -- Remote with User Interaction
Resolution: Mitigation
CVE Names: CVE-2009-3555
Reference: ASB-2009.1150
ESB-2010.0036.2
Original Bulletin:
http://www.microsoft.com/technet/security/advisory/977377.mspx
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Microsoft Security Advisory (977377)
Vulnerability in TLS/SSL Could Allow Spoofing
Published: February 09, 2010
Version: 1.0
General Information
Executive Summary
Microsoft is investigating public reports of a vulnerability in the
Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols.
At this time, Microsoft is not aware of any attacks attempting to exploit
the reported vulnerability.
As an issue affecting an Internet standard, we recognize that this issue
affects multiple vendors. We are working on a coordinated response with
our partners in the Internet Consortium for Advancement of Security on
the Internet (ICASI). The TLS and SSL protocols are implemented in
several Microsoft products, both client and server, and this
advisory will be updated as our investigation continues.
As part of this security advisory, Microsoft is making available a
workaround which enables system administrators to disable TLS and SSL
renegotiation functionality. However, as renegotiation is required
functionality for some applications, this workaround is not intended
for wide implementation and should be tested extensively prior to
implementation.
Upon completion of this investigation, Microsoft will take the
appropriate action to protect our customers, which may include providing
a solution through our monthly security update release process,
depending on customer needs.
Affected Software
Microsoft Windows 2000 Service Pack 4
Windows XP Service Pack 2 and Windows XP Service Pack 3
Windows XP Professional x64 Edition Service Pack 2
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 1, and Windows Vista Service
Pack 2
Windows Vista x64 Edition, Windows Vista x64 Edition Service Pack 1, and
Windows Vista x64 Edition Service Pack 2
Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit
Systems Service Pack 2
Windows Server 2008 for x64-based Systems and Windows Server 2008 for
x64-based Systems Service Pack
Windows Server 2008 for Itanium-based Systems and Windows Server 2008
for Itanium-based Systems Service Pack 2
Windows 7 for 32-bit Systems
Windows 7 for x64-based Systems
Windows Server 2008 R2 for x64-based Systems
Windows Server 2008 R2 for Itanium-based Systems
What is the scope of the advisory?
Microsoft is aware of a new report of a vulnerability affecting the
Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols.
This vulnerability could allow a malicious man-in-the-middle attack to
introduce and execute a request in the protected TLS/SSL session between a
client and a server.
Workarounds
Microsoft has tested the following workarounds. Although these workarounds
will not correct the underlying vulnerability, they help block known attack
vectors. When a workaround reduces functionality, it is identified in the
following section.
Enable SSLAlwaysNegoClientCert on IIS 6 and above
Web servers running IIS 6 and later that are affected because they require
mutual authentication by requesting a client certificate, can be hardened
by enabling the SSLAlwaysNegoClientCert setting. This will cause IIS to
prompt the client for a certificate upon the initial connection, and does
not require a server-initiated renegotiation.
For IIS 6:
Run the following command from the "c:\inetpub\adminscripts" folder in an
elevated / administrator command prompt:
adsutil.vbs SET w3svc/<N>/SSLAlwaysNegoClientCert true
Where <N> represents the number of the web site to be configured
(i.e. the 'Default Web Site' is 1, the next web site is 2, etc.).
So for example - to protect the 'Default Web Site' created by IIS the
following command would be used:
adsutil.vbs SET w3svc/1/SSLAlwaysNegoClientCert true
For IIS 7:
Save the following text to a file called
"Enable_SSL_Renegotiate_Workaround.js"
var vdirObj=GetObject("IIS://localhost/W3svc/1");
// replace 1 on this line with the number of the web site you wish
to configure
WScript.Echo("Value of SSLAlwaysNegoClientCert Before: " + vdirObj.SSLAlwaysNegoClientCert);
vdirObj.Put("SSLAlwaysNegoClientCert", true);
vdirObj.SetInfo();
WScript.Echo("Value of SSLAlwaysNegoClientCert After: " + vdirObj.SSLAlwaysNegoClientCert);
Run the following command from an elevated / administrator command
prompt:
cscript.exe enable_ssl_renegotiate_workaround.js
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