Microsoft Windows Keaccumulateticks Smb Packet Remote Denial Of Service Vulnerability

[Lauro Pericles]

Thissecurity update resolves one publicly disclosed and two privately reported vulnerabilities in Server Message Block Version 2 (SMBv2). The most severe of the vulnerabilities could allow remote code execution if an attacker sent a specially crafted SMB packet to a computer running the Server service. Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate from outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.

This security update is rated Critical for supported editions of Windows Vista and Windows Server 2008. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerabilities by correctly validating the fields inside the SMBv2 packets, correcting the way that SMB handles the command value in SMB packets, and correcting the way that SMB parses specially crafted SMB packets. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. The majority of customers have automatic updating enabled and will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers apply the update immediately using update management software, or by checking for updates using the Microsoft Update service.

The following software have been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, visit Microsoft Support Lifecycle.

*Windows Server 2008 Server Core installation affected. For supported editions of Windows Server 2008, this update applies, with the same severity rating, whether or not Windows Server 2008 was installed using the Server Core installation option. For more information on this installation option, see Server Core. Note that the Server Core installation option does not apply to certain editions of Windows Server 2008; see Compare Server Core Installation Options.

Does this update require the system to be restarted to take affect?

It is possible to update your system without restarting. To do this, you need to restart the Server SMB 2.x driver and all of the services that are dependent on this driver after applying the update. If this update is installed via automatic updates, you will be prompted to restart your system. However, the update may not notify you that a restart is required if you apply the update manually. Because the list of services can be quite long, we recommend restarting the system to ensure that the update is applied correctly.

Why does this update address several reported security vulnerabilities?

This update contains support for several vulnerabilities because the modifications that are required to address these issues are located in related files. Instead of having to install several updates that are almost the same, customers need to install this update only.

I am using an older release of the software discussed in this security bulletin. What should I do?

The affected software listed in this bulletin have been tested to determine which releases are affected. Other releases are past their support life cycle. To determine the support life cycle for your software release, visit Microsoft Support Lifecycle.

It should be a priority for customers who have older releases of the software to migrate to supported releases to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit Microsoft Support Lifecycle. For more information about the extended security update support period for these software versions or editions, visit Microsoft Product Support Services.

Customers who require custom support for older releases must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, visit Microsoft Worldwide Information, select the country, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Windows Operating System Product Support Lifecycle FAQ.

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the October bulletin summary. For more information, see Microsoft Exploitability Index.

A denial of service vulnerability exists in the way that Microsoft Server Message Block (SMB) Protocol software handles specially crafted SMB version 2 (SMBv2) packets. An attempt to exploit the vulnerability would not require authentication, allowing an attacker to exploit the vulnerability by sending a specially crafted network message to a computer running the Server service. An attacker who successfully exploited this vulnerability could cause the computer to stop responding until restarted.

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

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:

Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

Impact of workaround. The host will not communicate using SMBv2. Instead, the host will communicate using SMB 1.0. This should not impact basic services such as file and printer sharing. These will continue to function as normal.

These ports are used to initiate a connection with the affected component. Blocking TCP ports 139 and 445 at the firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability. Microsoft recommends that you block all unsolicited inbound communication from the Internet to help prevent attacks that may use other ports. For more information about ports, see TCP and UDP Port Assignments.

Impact of Workaround: Several Windows services use the affected ports. Blocking connectivity to the ports may cause various applications or services to not function. Some of the applications or services that could be impacted are listed below:

What is the scope of the vulnerability?

This is a denial of service vulnerability. An attacker who exploited this vulnerability could cause the affected system to stop responding until it is manually restarted. Note that the denial of service vulnerability would not allow an attacker to execute code or to elevate their user rights, but it could cause the affected system to stop accepting requests.

What causes the vulnerability?

The vulnerability is caused by the Microsoft Server Message Block (SMB) Protocol software insufficiently validating all fields when parsing specially crafted SMBv2 packets.

What is Server Message Block Version 2 (SMBv2)?

Server Message Block (SMB) is the file sharing protocol used by default on Windows-based computers. SMB Version 2.0 (SMBv2) is an update to this protocol, and is only supported on computers running Windows Server 2008, Windows 7, and Windows Vista. SMBv2 can only be used if both client and server support it. If either client or server cannot support SMBv2, the SMB 1.0 protocol will be used instead. The SMB protocol version to be used for file operations is decided during the negotiation phase. During the negotiation phase, a Windows Vista client advertises to the server that it can understand the new SMBv2 protocol. If the server (Windows Server 2008 or later) understands SMBv2, then SMBv2 is chosen for subsequent communication. Otherwise the client and server use SMB 1.0 and continue to function as normal. For more information on SMBv2, see MSDN article, Server Message Block (SMB) Version 2 Protocol Specification.

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