Hosts: Jonathan Ness, Security Development Manager, MSRC
Pete Voss, Sr. Response
Communications Manager, Trustworthy Computing
Chat Topic: December 2011
Out-Of-Band Security Bulletin Release
Date: Thursday, December 29, 2011
Q: How are Denial of
Service, Tampering, Information Disclosure orSpoofing issues rated?
A: The Exploitability Index only attempts to rate
vulnerabilities that can be leveraged for code execution. Vulnerabilities that could allow denial of service, tampering,
information disclosure or spoofing will receive an Exploitability Index rating of "3." The notes for that particular CVE will
also reflect the nature of the vulnerability.
Q: One angle I'm interested in is those Microsoft products that might use
forms authentication, such as Exchange 2010 or TMG 2010. If we're using forms authentication there, does that mean we're
A: Any products that are using ASP.NET forms authentication will be secured with this update. This includes SharePoint and
Exchange, when they are using ASP.NET forms authentication. If these products are using a Forms Authentication module other
than the one provided by ASP.NET, then the issue addressed in this bulletin does not apply to you.
Q: Why does Windows
Update on Windows 2008 servers show this update, but the check-box next to it is un-checked? What is the difference between
patches that are checked by default and those that are not checked?
A: In the case of "Important Updates", an update that is in the "PENDING" state will be unchecked when you view it in Windows
Update. This means it is already queued for downloading. You can manually override this to start the download manually by
checking the box next to the update.
Q: Please confirm that if an IIS instance is installed that we are at risk for
one of the CVE's and therefore we should patch ASAP. The assumption is that the server has IIS without .NET components.
A: By default, IIS is not installed with .NET and by default, .NET is not installed by ASP.NET. Customers would first need to
have installed .NET framework with ASP.NET in order to be vulnerable to the vulnerabilities documented by MS11-100.
What level of testing or specific tests is recommended for applications using ASP.NET? Is it highly likely that the hashing
change will impact applications using the framework?
A: Microsoft recommends that customers test this update before deploying. There is a change in how forms authentication
occurs and will require updates to be deployed at the same time across server environments. Click here for more about forms
Q: Can sample DoS requests be provided to allow us to understand what the DOS signature may look like
so we can test the patch as well as monitor our production environments until the patching is completed?
A: For more
technical information regarding MS11-100, please see the SRD blog, where we have shared a short signature detecting this
Q: Is this critical to environments where there are no Internet-facing systems? And what if there is no IIS
installed on the workstation -- is it atrisk?
A: Exploitation requires ASP.NET installed and to be exposed to input from unauthenticated users. Typically this is through
IIS. If workstations do not have ASP.NET or IIS installed, then those systems are not exposed.
Q: In the Critical
Elevation of Privilege can the attacker elevate is privilege only if they have the username without having the password? Can
we have machines with the fix and without the fix working with each other?
A: Yes, the attacker only needs the username to carry out the attack. The fix involves changing the format of the forms
authentication ticket, so that unpatched and patched machines cannot work with each other. So after patching you cannot have
machines with the fix and without it working together, unless you set a configuration setting on the patched machines. For
details, please read the FAQ for this CVE for more information on applying updates to web farms.
Q: For CVE-2011-3414,
is there a requirement of authentication to exploit the DoS vulnerability successfully?
A: No, CVE-2011-3414 is anunauthenticated Denial of Service.
Q: What could be a potential impact on server running IIS
with custom code? In short, can this update impact server or service to go down after installation? Do you have any
suggestions on installation on web servers running custom code?
A: This update is specifically for ASP.NET, but the issue that was disclosed is an industry-wide issue concerning hash
collisions. So, it is possible for your custom code to be affected, but you will need to investigate what kind of hash-tables
your custom code uses and if it operates on untrusted user data.
Q: Is there a client-side patch that will protect
users that fall for phishing attacks and visit websites that have not patched?
A: As clients are not affected by
server-sided vulnerability, the security update does need to be installed on the server.
Q: If the main target is
Internet facing systems with IIS & ASP.NET installed, should I concentrate on patching my webservers first before patching
A: Prioritization for this update would be specific to users’ environments, but servers that are internet-facing and
accept input from unauthenticated or untrusted user-provided content are most affected and should be prioritized. Likewise,
clients are typically not in a web server role, and so systems that are running a web server role should be prioritized.
Q: What steps can I take to reproduce and see if/how my site is affected, and so I can confirm the issue is gone after
applying the patch?
A: For the protection of customers, Microsoft does not disclose proof of concept code (POC). The
technical details of this issue are however public.
Q: If Microsoft .NET Framework is installed on an IIS Server, does
this mean that ASP.NET is also installed but possibly not enabled?
A: Whether you have the .NET Framework (and ASP.NET) installed on a machine will depend upon the specific OS platform.
Windows Server 2008, Windows Server 2008 SP2, Windows Server 2008 R2 and Windows Server 2008 R2 SP1 all ship with the .NET
Framework 2.0 or higher, which includes ASP.NET, and you should install the corresponding patches listed in the security
bulletin. If you are using an older Server OS such as Windows Server 2003 SP2 x86, then that platform includes .NET Framework
1.1 SP1, and you should install the corresponding patch listed in the security bulletin.
Q: From a desktop browsing
experience, this update will patch Windows XP, Vista and 7. If machines do not have IIS installed and enabled, as well as
ASP.NET enabled, is the criticality of this update reduced? For example if the user goes to an internet site, would their
desktop PC be vulnerable? It seems to be mostly if you have IIS and ASP.net installed and acting as a web server.
A: If you have a client machine with no ASP.NET installed, then your desktop PC would not be vulnerable to the particular
security issues that are being addressed in this update.
Q: ASP.Net has been identified for the DoS. How about classic
ASP/ISAPI applications? Is it just a .Net hash-table issue? And has the Microsoft Foundation Class / ATL / Visual Basic 6.0
A: This is an industry-wide issue that could affect a broad spectrum of technologies. Since ASP.NET was at the greatest risk
because of the public disclosure, we have focused our efforts so far on making sure we secure ASP.NET. We are actively
investigating other technologies where this could be vulnerable and so far we do not think that classic ASP is vulnerable.
Information on other affected technologies will be revealed as the issue develops.
Q: So just to be clear, Exchange
2010 Outlook Web Access isn't vulnerable to the privilege of escalation? Just to the DOS?
A: OWA 2010 can be configured for forms-based authentication. Based on this, it should be considered vulnerable. If there is
any doubt, Microsoft KB Article 2638420 discusses parameters you can check for to verify if an application is using forms
auth. Specifically, to determine whether your application uses forms authentication,
examine the System.web file. Applications that use forms authentication use the following entry in System.web file:
What tools are available to remotely scan systems to see if they’re vulnerable -- that is, that IIS and ASP are
installed and active?
A: The Detection and Deployment Tools and Guidance section in the security bulletin provides information on how to identify
systems to which this update applies. If you want to identify whether a system has IIS installed with ASP.NET enabled, the
answer depends on the operating system that each system is running.
Q: Are only webservers vulnerable? We have limited
personnel this weekend for QA and deployment. Are we pretty much covered if we just deploy to systems in our DMZ this weekend
and then rest of the enterprise next week?
A: Prioritization for this update would be specific to users’ environments, but servers that are internet-facing and
accept input from unauthenticated or untrusted user provided content may be at greater risk than internal servers.
Sites that disallow "application/x-www-form-urlencoded” or “multipart/form-data” HTTP content types are not
vulnerable. Is this set to disallow by default? How do we verify if it is set to disallow?
application/x-www-form-urlencoded or multipart/form-data are not disallowed by default. Customers will need to explicitly
disallow these. Customers can do this by using IIS request filtering.
Q: Forms authorization login from TMG/ISA
doesn't use ASP.NET. Is it still vulnerable?
A: TMG is not exposed and is not related to the ASP.NET issue described in the bulletin.
Q: Do you suggest immediate
patching of all servers (internal/external) or just of externally available servers and allow internal servers to be patched
during the next patching cycle?
A: Once again, prioritization for this update would be specific to each user’s environment, but servers that are
internet-facing and accept input from unauthenticated or untrusted user provided content may be at greater risk than internal
Q: Is the critical CVE related to forms authentication only an issue if the site is configured to support
forms authentication without cookies? Or, are all forms authentication implementations impacted?
A: No, this issue applies to all types of ASP.NET forms authentication, cookie and cookie-less.
Q: For CVE 2011-3414,
does the patch change the size of request header accepted, place controls on the amount of CPU that can be used, or change
the hashing functions used?
A:The security update addresses this issue by limiting the number of inputs ASP.NET accepts
Q: Does this patch limit the number of parameters passed in the post request? If so, what is the new
limit? I am trying to determine what application problems may arise after applying the update.
A: The security update addresses this issue by limiting the number of inputs ASP.NET accepts from clients. If you are
interested in changing the number of parameters passed in the post request, please see the section of the bulletin titled
Workarounds for Collisions in HashTable May Cause DoS Vulnerability - CVE-2011-3414.
Q: Can the normally scheduled
January bulletins be installed independently of the critical one?
A: Yes, Future security updates can be installed
independently of this issue. Microsoft does recommend all customers always read security updates to ensure they fully
understand any known issues that may be documented in the security bulletin.
Q: Is the attack vector based on the
server or the client? Do we concentrate on server or desktop side first?
A: The vulnerabilities in the bulletins are primarily focused on systems operating in a Web server role that use ASP.NET.
Clients are typically not in a web server role.
Q: Could you provide more detail around the 3rd mitigation factor --
specifically the account registration procedure?
A: I am assuming this question is about the first mitigating factor for CVE-2011-3416: forms authentication bypass.
Essentially, to pull off an Elevation of Privilege attack, the attacker would need a valid account on the system they are
trying to compromise and the user name of the target of the attack.
Q: Can an ASP.NET site (e.g. SharePoint 2010 site)
using authentication (NTLM/Kerberos) come under the DoS attack as described in CVE-2011-3414 by an unauthenticated user?
A: NTLM/Kerberos authentication changes the attack vector of the vulnerability. An ASP.NET site can come under a DOS attack
– however, the attacker would then need to be authenticated.
Q: Will this affect -- or will I need to be aware
of -- this update impacting ASP.NET session and machine key settings in IIS for a load balanced environment, where all
machine keys are matches to make sure sessions are the same across a server farm?
A: This update changes the way in which forms authentication tickets are created, so all servers would need to use the old or
the new ticket format in order to maintain compatibility. Please refer to Knowledge Base Article 2659968 for deployment
guidance for this update.
Q: What about servers that have IP address access limitations? Since we are resource-limited,
we'd like to skip these servers that are only allowing certain IPs to access IIS.
A: As we’ve mentioned, prioritization for this update would be specific to users environments, but servers that are
Internet-facing and can accept input from unauthenticated or untrusted user provided content may be at greater risk than
internal servers. Servers that have additional protections may reduce the potential attack risk of these vulnerabilities.
Customers are encouraged to analyze their own environments.
Q: We have ASP.NET prohibited in in our Web Service
Extensions -- IIS 6. Are we still vulnerable?
A: No. If ASP.NET is not enabled, you are not vulnerable.
Section Workarounds for Collisions in HashTable May Cause DoS Vulnerability - CVE-2011-3414 in the bulletin is confusing. Is
it required to put this script and then install the update?
A: Workaround refers to a setting or configuration change that does not correct the underlying vulnerability, but would help
block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the
discussion whether a workaround reduces functionality. Customers are always encouraged to apply the security update. The
workarounds are not a prerequisite for installing the security update.
Q: If TMG is not affected then, if TMG is
protecting an Exchange 2010 server and the TMG is handling the forum authorization, would the patch for an Exchange server be
A: Although firewall solutions could protect systems behind the firewall it is important to understand the
types of traffic that that FW may proxy to servers behind it. Systems behind the firewall are still vulnerable to internal
attacks and have vulnerable code and should be updated to be properly protected.
AppSettings.MaxHttpCollectionKeys the new parameter that contains the maximum number of form entries?
A: Yes it is.
Q: For ASP.NET on Internet-facing systems requiring authentication, does an attacker have to have a valid
user name AND the valid password to carry out an attack?
A: No. The only requirement is to have the target's username, and *any* valid account on the system.
Q: Will any forms
authentication tickets generated before the patch is applied be rendered invalid once the patch is applied?
A: Yes. The change in the forms authentication ticket format will render all pre-patch tickets invalid once the update is
[B]Q: Our ASP.NET application requires large file uploads and requires our