Microsoft Security Bulletin MS09-050 - Critical Vulnerabilities in SMBv2 Could Allow Remote Code Execution (975517)

Microsoft Security Bulletin MS09-050 - Critical
Vulnerabilities in SMBv2 Could Allow Remote Code Execution (975517)
Published: October 13, 2009

Version: 1.0
General Information
Executive Summary

This security 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.

This security update also addresses the vulnerability first described in Microsoft Security Advisory 975497.

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.

See also the section, Detection and Deployment Tools and Guidance, later in this bulletin.

Known Issues. None
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Affected and Non-Affected Software

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.

Affected Software
Operating System Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by this Update

Windows Vista, Windows Vista Service Pack 1, and Windows Vista Service Pack 2

Remote Code Execution

Critical

None

Windows Vista x64 Edition, Windows Vista x64 Edition Service Pack 1, and Windows Vista x64 Edition Service Pack 2

Remote Code Execution

Critical

None

Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2*

Remote Code Execution

Critical

None

Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2*

Remote Code Execution

Critical

None

Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2

Remote Code Execution

Critical

None

*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.

Non-Affected Software
Operating System

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 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
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Frequently Asked Questions (FAQ) Related to This Security Update

Where are the file information details?
Refer to the reference tables in the Security Update Deployment section for the location of the file information details.

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.
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Vulnerability Information

Severity Ratings and Vulnerability Identifiers

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.
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software SMBv2 Infinite Loop Vulnerability - CVE-2009-2526 SMBv2 Command Value Vulnerability - CVE-2009-2532 SMBv2 Negotiation Vulnerability - CVE-2009-3103 Aggregate Severity Rating

Windows Vista, Windows Vista Service Pack 1, and Windows Vista Service Pack 2

Important
Denial of Service

Critical
Remote Code Execution

Critical
Remote Code Execution

Critical

Windows Vista x64 Edition, Windows Vista x64 Edition Service Pack 1, and Windows Vista x64 Edition Service Pack 2

Important
Denial of Service

Critical
Remote Code Execution

Critical
Remote Code Execution

Critical

Windows Server 2008 for 32-bit Systems and Windows Server 2008 for 32-bit Systems Service Pack 2*

Important
Denial of Service

Critical
Remote Code Execution

Critical
Remote Code Execution

Critical

Windows Server 2008 for x64-based Systems and Windows Server 2008 for x64-based Systems Service Pack 2*

Important
Denial of Service

Critical
Remote Code Execution

Critical
Remote Code Execution

Critical

Windows Server 2008 for Itanium-based Systems and Windows Server 2008 for Itanium-based Systems Service Pack 2

Important
Denial of Service

Critical
Remote Code Execution

Critical
Remote Code Execution

Critical

*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.
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SMBv2 Infinite Loop Vulnerability - CVE-2009-2526

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.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2009-2526.

Mitigating Factors for SMBv2 Infinite Loop Vulnerability - CVE-2009-2526

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:
•

Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.
•

In Windows Vista, if the network profile is set to "Public", the system is not affected by this vulnerability since unsolicited inbound network packets are blocked by default.
•

The Release to Manufacturing (RTM) versions of Windows 7 and Windows Server 2008 R2 are not affected by this vulnerability.
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Workarounds for SMBv2 Infinite Loop Vulnerability - CVE-2009-2526

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:
•

Disable SMB v2

Note See Microsoft Knowledge Base Article 975517 to use the automated Microsoft Fix it solution to enable or disable this workaround.

To modify the registry key, perform the following steps:

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.

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Right-click to add a new DWORD (32 bit) Value.

Enter smb2 in the Name data field, and change the Value data field to 0.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.

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.

How to undo the workaround:

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Double-click smb2, and change the Value data field to 1.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.
  •

Block TCP ports 139 and 445 at the firewall

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:
•

Applications that use SMB (CIFS)
•

Applications that use mailslots or named pipes (RPC over SMB)
•

Server (File and Print Sharing)
•

Group Policy
•

Net Logon
•

Distributed File System (DFS)
•

Terminal Server Licensing
•

Print Spooler
•

Computer Browser
•

Remote Procedure Call Locator
•

Fax Service
•

Indexing Service
•

Performance Logs and Alerts
•

Systems Management Server
•

License Logging Service

How to undo the workaround. Unblock TCP ports 139 and 445 at the firewall. For more information about ports, see TCP and UDP Port Assignments.
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FAQ for SMBv2 Infinite Loop Vulnerability - CVE-2009-2526

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.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could cause a user's system to stop responding until manually restarted.

How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by creating a specially crafted SMBv2 packet and sending the packet to an affected system.

What systems are primarily at risk from the vulnerability?
All systems with SMB Server service are affected by this vulnerability. Domain controllers are at a greater risk for this vulnerability, as these systems have network shares open to all domain users by default.

What does the update do?
The security update addresses the vulnerability by correctly validating the fields inside the SMBv2 packets.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.
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SMBv2 Command Value Vulnerability - CVE-2009-2532

An unauthenticated remote code execution vulnerability exists in the way that Microsoft Server Message Block (SMB) Protocol software handles specially crafted SMB 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 take complete control of the system.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2009-2532.

Mitigating Factors for SMBv2 Command Value Vulnerability - CVE-2009-2532

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:
•

Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.
•

In Windows Vista, if the network profile is set to "Public", the system is not affected by this vulnerability since unsolicited inbound network packets are blocked by default.
•

The Release to Manufacturing (RTM) versions of Windows 7 and Windows Server 2008 R2 are not affected by this vulnerability.
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Workarounds for SMBv2 Command Value Vulnerability - CVE-2009-2532

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:
•

Disable SMB v2

Note See Microsoft Knowledge Base Article 975517 to use the automated Microsoft Fix it solution to enable or disable this workaround.

To modify the registry key, perform the following steps:

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.

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Right-click to add a new DWORD (32 bit) Value.

Enter smb2 in the Name data field, and change the Value data field to 0.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.

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.

How to undo the workaround:

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Double-click smb2, and change the Value data field to 1.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.
  •

Block TCP ports 139 and 445 at the firewall

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:
•

Applications that use SMB (CIFS)
•

Applications that use mailslots or named pipes (RPC over SMB)
•

Server (File and Print Sharing)
•

Group Policy
•

Net Logon
•

Distributed File System (DFS)
•

Terminal Server Licensing
•

Print Spooler
•

Computer Browser
•

Remote Procedure Call Locator
•

Fax Service
•

Indexing Service
•

Performance Logs and Alerts
•

Systems Management Server
•

License Logging Service

How to undo the workaround. Unblock TCP ports 139 and 445 at the firewall. For more information about ports, see TCP and UDP Port Assignments.
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FAQ for SMBv2 Command Value Vulnerability - CVE-2009-2532

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

What causes the vulnerability?
The vulnerability is caused by the Microsoft Server Message Block (SMB) implementation not using the validated copy of the command value when handling SMB Multi-Protocol Negotiate Request 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.

Is the Windows 7 Release Candidate (RC) release affected by this vulnerability?
Yes. This vulnerability was discovered after the release of Windows 7 Release Candidate. Customers running Windows 7 Release Candidate are encouraged to download and apply the update to their systems. The final versions of Windows 7 and Windows Server 2008 R2 are not affected by this vulnerability.

Security updates are available from Microsoft Update and Windows Update. Security updates are also available from the Microsoft Download Center. You can find them most easily by doing a keyword search for "security update."

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of an affected system.

How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by creating a specially crafted SMB packet and sending the packet to an affected system.

What systems are primarily at risk from the vulnerability?
All systems with the SMB Server service are affected by this vulnerability. Domain controllers are at a greater risk for this vulnerability, as these systems have network shares open to all domain users by default.

What does the update do?
The update addresses the vulnerability by correcting the way that SMB handles the command value in SMB packets.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.
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SMBv2 Negotiation Vulnerability - CVE-2009-3103

An unauthenticated remote code execution vulnerability exists in the way that Microsoft Server Message Block (SMB) Protocol software handles specially crafted SMB packets. An attempt to exploit the vulnerability would not require authentication, allowing an attacker to exploit the vulnerability by sending a specially crafted SMB packet to a computer running the Server service. An attacker who successfully exploited this vulnerability could take complete control of the system.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2009-3103.

Mitigating Factors for SMBv2 Negotiation Vulnerability - CVE-2009-3103

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:
•

Firewall best practices and standard default firewall configurations can help protect networks from attacks that originate outside the enterprise perimeter. Best practices recommend that systems that are connected to the Internet have a minimal number of ports exposed.
•

In Windows Vista, if the network profile is set to "Public", the system is not affected by this vulnerability since unsolicited inbound network packets are blocked by default.
•

The Release to Manufacturing (RTM) versions of Windows 7 and Windows Server 2008 R2 are not affected by this vulnerability.
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Workarounds for SMBv2 Negotiation Vulnerability - CVE-2009-3103

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:
•

Disable SMB v2

Note See Microsoft Knowledge Base Article 975517 to use the automated Microsoft Fix it solution to enable or disable this workaround.

To modify the registry key, perform the following steps:

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.

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Right-click to add a new DWORD (32 bit) Value.

Enter smb2 in the Name data field, and change the Value data field to 0.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.

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.

How to undo the workaround:

Click Start, click Run, type Regedit in the Open box, and then click OK.

Locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services

Click LanmanServer.

Click Parameters.

Double-click smb2, and change the Value data field to 1.

Exit.

Restart the "Server" service by performing one of the following:

• Open up the computer management MMC, navigate to Services and Applications, click Services, right-click the Server service name and click Restart. Answer Yes in the pop-up menu.

• From a command prompt and with administrator privileges, type net stop server and then net start server.
  •

Block TCP ports 139 and 445 at the firewall

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:
•

Applications that use SMB (CIFS)
•

Applications that use mailslots or named pipes (RPC over SMB)
•

Server (File and Print Sharing)
•

Group Policy
•

Net Logon
•

Distributed File System (DFS)
•

Terminal Server Licensing
•

Print Spooler
•

Computer Browser
•

Remote Procedure Call Locator
•

Fax Service
•

Indexing Service
•

Performance Logs and Alerts
•

Systems Management Server
•

License Logging Service

How to undo the workaround. Unblock TCP ports 139 and 445 at the firewall. For more information about ports, see TCP and UDP Port Assignments.
Top of sectionTop of section

FAQ for SMBv2 Negotiation Vulnerability - CVE-2009-3103

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could take complete control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

What causes the vulnerability?
The vulnerability is caused by the Microsoft Server Message Block (SMB) implementation not appropriately parsing SMB 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.

Is the Windows 7 Release Candidate (RC) release affected by this vulnerability?
Yes. This vulnerability was discovered after the release of Windows 7 Release Candidate. Customers running Windows 7 Release Candidate are encouraged to download and apply the update to their systems. The final versions of Windows 7 and Windows Server 2008 R2 are not affected by this vulnerability.

Security updates are available from Microsoft Update and Windows Update. Security updates are also available from the Microsoft Download Center. You can find them most easily by doing a keyword search for "security update."

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of an affected system.

How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by creating a specially crafted SMB packet and sending the packet to an affected system.

What systems are primarily at risk from the vulnerability?
All systems with the SMB Server service are affected by this vulnerability. Domain controllers are at a greater risk for this vulnerability, as these systems have network shares open to all domain users by default.

What does the update do?
The update addresses the vulnerability by correcting the way that SMB parses specially crafted SMB packets.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. This vulnerability has been publicly disclosed. It has been assigned Common Vulnerability and Exposure number CVE-2009-3103.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had not received any information to indicate that this vulnerability had been publicly used to attack customers and had not seen any examples of proof of concept code published when this security bulletin was originally issued.

Other Information
Acknowledgments

Microsoft thanks the following for working with us to help protect customers:
•

Matthieu Suiche of the Netherlands Forensics Institute for reporting the SMBv2 Command Value Vulnerability (CVE-2009-2532)
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Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please visit the active protections Web sites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.

Support
•

Customers in the U.S. and Canada can receive technical support from Security Support or 1-866-PCSAFETY. There is no charge for support calls that are associated with security updates. For more information about available support options, see Microsoft Help and Support.
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International customers can receive support from their local Microsoft subsidiaries. There is no charge for support that is associated with security updates. For more information about how to contact Microsoft for support issues, visit the International Support Web site.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.
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Revisions
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V1.0 (October 13, 2009): Bulletin published.