Microsoft Security Bulletin MS06-064 Vulnerabilities in TCP/IP IPv6 Could Allow Denial of Service (922819)

Microsoft Security Bulletin MS06-064
Vulnerabilities in TCP/IP IPv6 Could Allow Denial of Service (922819)
Published: October 10, 2006

Version: 1.0
Summary

Who Should Read this Document: Customers who use Microsoft Windows.

Impact of Vulnerability: Denial of Service

Maximum Severity Rating: Low

Recommendation: Customers should evaluate whether to apply the security update to the affected systems.

Security Update Replacement: None

Tested Software and Security Update Download Locations:

Affected Software:
•

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2 — Download the update
•

Microsoft Windows XP Professional x64 Edition — Download the update
•

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1 — Download the update
•

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with SP1 for Itanium-based Systems — Download the update
•

Microsoft Windows Server 2003 x64 Edition — Download the update

Non-Affected Software:
•

Microsoft Windows 2000 Service Pack 4

The software in this list has been tested to determine whether the versions are affected. Other versions either no longer include security update support or may not be affected. To determine the support life cycle for your product and version, visit the Microsoft Support Lifecycle Web site.

Note The security updates for Microsoft Windows Server 2003, Windows Server 2003 Service Pack 1, and Windows Server 2003 x64 Edition also apply to Windows Server 2003 R2.
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General Information

Executive Summary

Executive Summary:

This update resolves a publicly disclosed vulnerability as well as additional issues discovered through internal investigations.

An attacker who successfully exploited the most severe of these vulnerabilities against an affected system could cause the system to stop responding or automatically reboot.

We recommend that customers evaluate whether to apply the security update to the affected systems.

Severity Ratings and Vulnerability Identifiers:
Vulnerability Identifiers Impact of Vulnerability Windows XP Service Pack 1 Windows XP Service Pack 2 Windows Server 2003 Windows Server 2003 Service Pack 1

ICMP Connection Reset Vulnerability - CVE-2004-0790

Denial of Service

Low

Low

Low

Low

TCP Connection Reset Vulnerability - CVE-2004-0230

Denial of Service

Low

Low

Low

Low

Spoofed Connection Request Vulnerability - CVE-2005-0688

Denial of Service

Low

Low

Low

Low

Aggregate Severity of All Vulnerabilities

Low

Low

Low

Low

This assessment is based on the types of systems that are affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them.

Note The security updates for Windows Server 2003, Windows Server 2003 Service Pack 1, and Windows Server 2003 x64 Edition also apply to Windows Server 2003 R2.

Note The severity ratings for non-x86 operating system versions map to the x86 operating systems versions as follows:
•

The Windows XP Professional x64 Edition severity rating is the same as the Windows Server 2003 Service Pack 1.
•

The Windows Server 2003 for Itanium-based Systems severity rating is the same as the Windows Server 2003 severity rating.
•

The Windows Server 2003 with SP1 for Itanium-based Systems severity rating is the same as the Windows Server 2003 Service Pack 1 severity rating.
•

The Windows Server 2003 x64 Edition severity rating is the same as the Windows Server 2003 Service Pack 1 severity rating.
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Frequently Asked Questions (FAQ) Related to This Security Update

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 can install only this update.

Does this security update contain any non-security changes to functionality?
Yes. In addition to the changes that are listed in the "Vulnerability Details" section, this update includes the Teredo Interoperability update for Windows XP Service Pack 2. Windows Server 2003 does not support Teredo and is not receiving the Teredo functionality change.

What is the Teredo interoperability update?
IANA has allocated a new Teredo prefix 2001:0/32 for Teredo. In order to establish connectivity over Teredo between Windows XP Service Pack 2 IPv6 capable hosts and Windows Vista, the Teredo prefix is being revised on all Windows XP machines. To learn more about Teredo please visit the following Microsoft TechNet documentation. To learn more about the new Teredo prefix, please visit the following RFC documentation.

Does this security update make any changes to the IPv4 implementation of TCP/IP?
No. The security issues addressed by this bulletin have already been resolved in the corresponding IPv4 implementation of TCP/IP with the release of the MS05-019.

Extended security update support for Microsoft Windows 98, Windows 98 Second Edition, or Windows Millennium Edition ended on July 11, 2006. I am still using one of these operating systems; what should I do?
Windows 98, Windows 98 Second Edition, and Windows Millennium Edition have reached the end of their support life cycles. It should be a priority for customers who have these operating system versions to migrate to supported versions to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit the following Microsoft Support Lifecycle Web site. For more information about the extended security update support period for these operating system versions, visit the Microsoft Product Support Services Web site.

Extended security update support for Microsoft Windows NT Workstation 4.0 Service Pack 6a and Windows 2000 Service Pack 2 ended on June 30, 2004. Extended security update support for Microsoft Windows NT Server 4.0 Service Pack 6a ended on December 31, 2004. Extended security update support for Microsoft Windows 2000 Service Pack 3 ended on June 30, 2005. I am still using one of these operating systems; what should I do?
Windows NT Workstation 4.0 Service Pack 6a, Windows NT Server 4.0 Service Pack 6a, Windows 2000 Service Pack 2, and Windows 2000 Service Pack 3 have reached the end of their support life cycles. It should be a priority for customers who have these operating system versions to migrate to supported versions to prevent potential exposure to vulnerabilities. For more information about the Windows Product Lifecycle, visit the following Microsoft Support Lifecycle Web site. For more information about the extended security update support period for these operating system versions, visit the Microsoft Product Support Services Web site.

Customers who require custom support for these products 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 the Microsoft Worldwide Information Web site, 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.

Can I use the Microsoft Baseline Security Analyzer (MBSA) to determine whether this update is required?
The following table provides the MBSA detection summary for this security update.
Product MBSA 1.2.1 MBSA 2.0

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2

Yes

Yes

Microsoft Windows XP Professional x64 Edition

No

Yes

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1

Yes

Yes

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with Service Pack 1 for Itanium-based Systems

No

Yes

Microsoft Windows Server 2003 x64 Edition family

No

Yes

For more information about MBSA, visit the MBSA Web site. For more information about the programs that Microsoft Update and MBSA 2.0 currently do not detect, see Microsoft Knowledge Base Article 895660.

For more detailed information, see Microsoft Knowledge Base Article 910723.

Can I use Systems Management Server (SMS) to determine whether this update is required?
The following table provides the SMS detection summary for this security update.
Product SMS 2.0 SMS 2003

Microsoft Windows XP Service Pack 1 and Microsoft Windows XP Service Pack 2

Yes

Yes

Microsoft Windows XP Professional x64 Edition

No

Yes

Microsoft Windows Server 2003 and Microsoft Windows Server 2003 Service Pack 1

Yes

Yes

Microsoft Windows Server 2003 for Itanium-based Systems and Microsoft Windows Server 2003 with Service Pack 1 for Itanium-based Systems

No

Yes

Microsoft Windows Server 2003 x64 Edition family

No

Yes

SMS 2.0 and SMS 2003 Software Update Services (SUS) Feature Pack can use MBSA 1.2.1 for detection and therefore have the same limitation that is listed earlier in this bulletin related to programs that MBSA 1.2.1 does not detect.

For more information about SMS, visit the SMS Web site.

For more detailed information, see Microsoft Knowledge Base Article 910723.
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Vulnerability Details

ICMP Connection Reset Vulnerability - CVE-2004-0790:

A denial of service vulnerability exists in the IPv6 Windows implementation of the Internet Control Message Protocol (ICMP). An attacker who successfully exploited this vulnerability could cause the affected system to drop an existing TCP connection.

Mitigating Factors for ICMP Connection Reset Vulnerability - CVE-2004-0790:
•

Firewall best practices and firewall or router configurations that block all ICMP traffic 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.
•

IPv6 support is not installed by default on Windows XP Service Pack 1, Windows XP Service Pack 2, Windows Server 2003 and Windows Server 2003 Service Pack 1.
•

An attacker’s system must belong to the same IPv6 network as the target system.
•

An attacker must first predict or discover the IP address and port information of the source and of the destination of an existing TCP network connection.
•

This attack would have to be performed on each TCP connection that was targeted for reset. Many applications will automatically restore connections that have been reset.
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Workarounds for ICMP Connection Reset Vulnerability - CVE-2004-0790:

Microsoft has tested the following workarounds. While 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.
•

Uninstall IPv6.

For the IPv6 protocol for Windows XP with SP2, Windows XP with SP1, or Windows Server 2003, do the following:

Log on to the computer with a user account that has privileges to change network configuration.

Click Start, click Control Panel, and then double-click Network Connections.

Click Microsoft TCP/IP version 6 (for Windows XP with SP2 or Windows Server 2003) or Microsoft IPv6 Developer Edition (for Windows XP with SP1), and then click Uninstall.

When prompted to confirm the removal of the Microsoft IPv6 Developer Edition or Microsoft TCP/IP version 6 protocol, click OK.

Alternately, from the Windows XP or Windows Server 2003 desktop do the following:

Click Start, point to Programs, point to Accessories.

Click Command Prompt.

At the command prompt, type netsh interface ipv6 uninstall.

Impact of Workaround: Uninstalling IPv6 would result in the system not being able to communicate with other hosts on an IPv6 configured network.
•

Block all ICMP network packets at the firewall or at the router:

ICMP network packets are used to initiate a connection with the affected components. Blocking them at the firewall or at the router will help protect systems that are behind that firewall or router from attempts to exploit this vulnerability. We recommend that you block all unsolicited inbound communication from the Internet.

Impact of Workaround: This workaround can also negatively impact performance by preventing TCP from optimizing network communication. ICMP network packets can eliminate fragmentation at routers connecting networks with different MTUs. Fragmentation reduces TCP throughput and increases network congestion.

Note: Windows XP Service Pack 1 Firewall is unable to handle IPv6 network traffic. In order to ensure protection for your Windows XP Service Pack 1 system using the Internet Connection Firewall you should apply the update identified in KB Article 817778 “Overview of the Advanced Networking Pack for Windows XP”.
•

Block ICMP traffic by using IPSec on the affected systems.

Use Internet Protocol security (IPSec) to help protect network communications. Detailed information about IPSec and about how to apply filters is available in Microsoft Knowledge Base Article 313190 and Microsoft Knowledge Base Article 813878.

Impact of Workaround: This workaround can also negatively impact performance by preventing TCP from optimizing network communication. ICMP network packets can eliminate fragmentation at routers connecting networks with different MTUs. Fragmentation reduces TCP throughput and increases network congestion.
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FAQ for ICMP Connection Reset Vulnerability - CVE-2004-0790:

What is the scope of the vulnerability?

A denial of service vulnerability exists in Windows in the IPv6 implementation of the Internet Control Message Protocol (ICMP). An attacker who successfully exploited this vulnerability could cause the affected system to drop an existing TCP connection.

What causes the vulnerability?
Specially crafted ICMP packets are being parsed when they should be dropped which may cause the reset of an existing connection.

What is IPv6?
Internet Protocol version 6 (IPv6), a new suite of standard protocols for the network layer of the Internet, is built into Microsoft Windows XP and later. IPv6 is designed to solve many of the problems of the current version of IP (known as IPv4) such as address depletion, security, autoconfiguration, and extensibility. To learn more about IPv6, please read the following Microsoft FAQ for IPv6.

What is TCP/IP?
TCP/IP is a set of networking protocols. TCP/IP includes standards for how computers communicate and conventions for connecting networks and for routing traffic. For more information about TCP/IP, see the following Microsoft Web site.

What is ICMP?
Internet Control Message Protocol (ICMP) is a required TCP/IP standard. "Internet Control Message Protocol (ICMP)." Hosts and routers that use IP communication can report errors and exchange limited control and status information using ICMP.

ICMP messages are usually sent automatically in one of the following situations:
•

An IP datagram cannot reach its destination.
•

An IP router (gateway) cannot forward datagrams at the current rate of transmission.
•

An IP router redirects the sending host to a better route to the destination.

You can use the ping command to send ICMP echo request messages and to record the receipt of ICMP echo reply messages. By using these messages, you can detect network or host communication failures and troubleshoot common TCP/IP connectivity problems. For more information about ICMP, see the following Microsoft Web site.

What might an attacker use the vulnerability to do?
An attacker who exploited this vulnerability could cause the affected system to reset TCP connections.

Who could exploit the vulnerability?
Any anonymous user who could deliver a specially crafted message to the affected system could try to exploit this vulnerability. An attacker’s system must belong to the same IPv6 network as a target system.

How could an attacker exploit the vulnerability?
An attacker could exploit the vulnerability by creating a specially crafted message and sending the message to an affected system. The message could then cause the affected system to reset TCP network connections.

What systems are primarily at risk from the vulnerability?
All affected operating systems are at risk from this vulnerability. However, servers are at primary risk from this vulnerability because they maintain connections with clients that could be vulnerable to the connection reset.

Could the vulnerability be exploited over the Internet?
Yes. An attacker could try to exploit this vulnerability over the Internet. By default, the Microsoft Internet Connection Firewall (ICF) in Windows XP Service Pack 1 and in Windows Server 2003 allows these kinds of network packets and cannot be used to filter them by default. The firewall component in Windows XP Service Pack 2 and Windows Server 2003 Service Pack 1 called Windows Firewall is able to block this traffic. If you are running IPv6 on a Windows XP Service Pack 1 you should apply update identified in KB Article 817778 “Overview of the Advanced Networking Pack for Windows XP” to get an updated Internet Connection Firewall which is able to handle IPv6 traffic.

What does the update do?
The update removes the vulnerability by modifying the way that the affected operating systems validate ICMP requests.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. This vulnerability has been publicly disclosed as affecting the IPv4 implementation of TCP/IP. It has been assigned Common Vulnerability and Exposure number CVE-2004-0790. There is a variant of this issue that has been assigned Common Vulnerability and Exposure number CVE-2004-0791. The Microsoft security update for CVE-2004-0790 also addresses CVE-2004-0791.

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.

How does this vulnerability relate to the vulnerability that is corrected by MS05-019?
MS05-19 addressed the same vulnerability in the more commonly adopted and deployed IPv4 implementation of TCP/IP. This update addresses the vulnerability in the IPv6 implementation.
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TCP Connection Reset Vulnerability - CVE-2004-0230:

A denial of service vulnerability exists in the IPv6 Windows implementation of TCP. An attacker who successfully exploited this vulnerability could cause the affected system to drop an existing TCP connection.

Mitigating Factors for TCP Connection Reset Vulnerability - CVE-2004-0230:
•

An attacker must be able to predict or discover the IP address and port information of the source and of the destination of an existing TCP network connection. An attacker would also have to predict or to learn certain difficult TCP network packet details. Protocols or programs that maintain long sessions and have predictable TCP/IP information are at an increased risk for this issue.
•

IPv6 support is not installed by default on Windows XP Service Pack 1 and Windows XP Service Pack 2, Windows Server 2003 and Windows Server 2003 Service Pack 1.
•

An attacker’s system must belong to the same IPv6 network as the target system.
•

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. Affected systems that allow any TCP connections to the Internet may be vulnerable to this issue.
•

This attack would have to be performed on each TCP connection that was targeted for reset. Many applications will automatically restore connections that have been reset.
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Workarounds for TCP Connection Reset Vulnerability - CVE-2004-0230:

Microsoft has tested the following workarounds. While 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.
•

Uninstall IPv6.

For the IPv6 protocol for Windows XP with SP2, Windows XP with SP1, or Windows Server 2003, do the following:

Log on to the computer with a user account that has privileges to change network configuration.

Click Start, click Control Panel, and then double-click Network Connections.

Click Microsoft TCP/IP version 6 (for Windows XP with SP2 or Windows Server 2003) or Microsoft IPv6 Developer Edition (for Windows XP with SP1), and then click Uninstall.

When prompted to confirm the removal of the Microsoft IPv6 Developer Edition or Microsoft TCP/IP version 6 protocol, click OK.

Alternately, from the Windows XP or Windows Server 2003 desktop do the following:

Click Start, point to Programs, point to Accessories.

Click Command Prompt.

At the command prompt, type netsh interface ipv6 uninstall.

Impact of Workaround: Uninstalling IPv6 would result in the system not being able to communicate with other hosts on an IPv6 configured network.
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FAQ for TCP Connection Reset Vulnerability - CVE-2004-0230:

What is the scope of the vulnerability?
A denial of service vulnerability exists in the IPv6 Windows implementation of TCP. An attacker who successfully exploited this vulnerability could cause the affected system to drop an existing TCP connection.

What causes the vulnerability?
Specially crafted TCP packets are being parsed when they should be dropped which may cause the reset of an existing connection.

What is IPv6?
Internet Protocol version 6 (IPv6), a new suite of standard protocols for the network layer of the Internet, is built into Microsoft Windows XP and later. IPv6 is designed to solve many of the problems of the current version of IP (known as IPv4) such as address depletion, security, autoconfiguration, and extensibility. To learn more about IPv6, please read the following Microsoft FAQ for IPv6.

What is TCP/IP?
TCP/IP is a set of networking protocols. TCP/IP includes standards for how computers communicate and conventions for connecting networks and for routing traffic. For more information about TCP/IP, see the following Microsoft Web site.

What might an attacker use the vulnerability to do?
An attacker who exploited this vulnerability could cause the affected system to reset TCP connections.

Who could exploit the vulnerability?
Any anonymous user who could deliver a specially crafted message to the affected system and learn or predict the required TCP details could try to exploit this vulnerability. An attacker’s system must belong to the same IPv6 network as a target system.

How could an attacker exploit the vulnerability?
An attacker could exploit the vulnerability by creating a specially crafted message and sending the message to an affected system. The message could then cause the affected system to reset TCP connections.

An attacker must be able to predict or discover the IP address and port information of the source and of the destination of an existing TCP network connection. An attacker would also have to predict or learn certain difficult TCP network packet details.

What systems are primarily at risk from the vulnerability?
All affected operating systems are at risk from this vulnerability. However, servers are at primary risk from this vulnerability because they maintain connections with clients that could be vulnerable to the connection reset. Protocols or programs that maintain long sessions and have predictable TCP/IP information are at an increased risk to this issue.

Could the vulnerability be exploited over the Internet?
Yes. An attacker could try to exploit this vulnerability over the Internet.

What does the update do?
The update removes the vulnerability by modifying the way that the affected operating systems validate TCP requests.

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-2004-0230.

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

Does applying this security update help protect customers from the code that has been published publicly that attempts to exploit this vulnerability?
Yes. This security update addresses the proof of concept code that has been publicly published. The vulnerability that has been addressed has been assigned the Common Vulnerability and Exposure number CVE-2004-0230.

How does this vulnerability relate to the vulnerability that is corrected by MS05-019?
MS05-19 addressed the same vulnerability in the more commonly adopted and deployed IPv4 implementation of TCP/IP. This update addresses the vulnerability in the IPv6 implementation.
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Spoofed Connection Request Vulnerability - CVE-2005-0688:

A denial of service vulnerability exists in Windows in the IPv6 implementation of TCP/IP. An attacker who successfully exploited this vulnerability could cause the affected system to stop responding.

Mitigating Factors for Spoofed Connection Request Vulnerability - CVE-2005-0688:
•

IPv6 support is not installed by default on Windows XP Service Pack 1, Windows XP Service Pack 2 and Windows Server 2003 and Windows Server 2003 Service Pack 1.
•

An attacker’s system must belong to the same IPv6 network as the target system.
•

The affected system return to a normal operational state after the specially crafted packets are finished processing.
•

A typical network deployment scenario would limit the attack to an individual network segment as most routers will not forward these kinds of specially crafted TCP/IP network packets.
•

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. Affected systems that allow any IP connections to the Internet may be vulnerable to this issue.
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Workarounds for Spoofed Connection Request Vulnerability - CVE-2005-0688:

Microsoft has tested the following workarounds. While 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.
•

Uninstall IPv6.

For the IPv6 protocol for Windows XP with SP2, Windows XP with SP1, or Windows Server 2003, do the following:

Log on to the computer with a user account that has privileges to change network configuration.

Click Start, click Control Panel, and then double-click Network Connections.

Click Microsoft TCP/IP version 6 (for Windows XP with SP2 or Windows Server 2003) or Microsoft IPv6 Developer Edition (for Windows XP with SP1), and then click Uninstall.

When prompted to confirm the removal of the Microsoft IPv6 Developer Edition or Microsoft TCP/IP version 6 protocol, click OK.

Alternately, from the Windows XP or Windows Server 2003 desktop do the following:

Click Start, point to Programs, point to Accessories.

Click Command Prompt.

At the command prompt, type netsh interface ipv6 uninstall.

Impact of Workaround: Uninstalling IPv6 would result in the system not being able to communicate with other hosts on an IPv6 configured network.
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FAQ for Spoofed Connection Request Vulnerability - CVE-2005-0688:

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 for a limited time as a result of excessive CPU utilization. During that time, affected systems cannot respond to requests. Note that the denial of service vulnerability would not allow an attacker to execute code or elevate their user rights, but it could cause the affected system to stop accepting requests.

What causes the vulnerability?
The affected operating systems perform incomplete validation of TCP/IP network packets. This vulnerability occurs when a Transmission Control Protocol (TCP) SYN packet is received with a spoofed source Internet Protocol (IP) address and port number that is identical to that of the destination IP address and port. The effect of this makes it appear that the host computer has sent a packet to itself. If this attack is successful, a loop is created and extra computer CPU time is used.

What is IPv6?
Internet Protocol version 6 (IPv6), a new suite of standard protocols for the network layer of the Internet, is built into Microsoft Windows XP and later. IPv6 is designed to solve many of the problems of the current version of IP (known as IPv4) such as address depletion, security, autoconfiguration, and extensibility. To learn more about IPv6, please read the following FAQ for IPv6.

What is TCP/IP?
TCP/IP is a set of networking protocols. TCP/IP includes standards for how computers communicate and conventions for connecting networks and for routing traffic. For more information about TCP/IP, see the following. For more information about TCP/IP, see the following Microsoft Web site.

What might an attacker use the vulnerability to do?
An attacker who exploited this vulnerability could cause the affected system to stop responding.

Who could exploit the vulnerability?
Any anonymous user who could deliver a specially crafted message to the affected system could try to exploit this vulnerability.

How could an attacker exploit the vulnerability?
An attacker could exploit the vulnerability by creating a specially crafted message and sending the message to an affected system. The message could then cause the affected system to stop responding.

What systems are primarily at risk from the vulnerability?
All affected operating systems are at risk from this vulnerability.

Could the vulnerability be exploited over the Internet?
Yes. An attacker could try to exploit this vulnerability over the Internet. However, this attack requires that routers forward malformed TCP/IP network packets. Most routers will not forward these kinds of malformed TCP/IP network packets.

What does the update do?
The update removes the vulnerability by modifying the way that the affected operating systems validate TCP/IP requests.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
Yes. This vulnerability has been publicly disclosed for the IPv4 implementation of TCP/IP. It has been assigned Common Vulnerability and Exposure number CVE-2005-0688. It also has been named “Land Attack” by the larger security community.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited?
No. Microsoft had seen examples of proof of concept code published publicly but had not received any information to indicate that this vulnerability had been publicly used to attack customers using IPv6 when this security bulletin was originally issued.

Does applying this security update help protect customers from the code that has been published publicly that attempts to exploit this vulnerability?
Yes. This security update addresses the vulnerability that is demonstrated by the existing proof of concept code that has been published.

How does this vulnerability relate to the vulnerability that is corrected by MS05-019?
MS05-19 addressed the same vulnerability in the more commonly adopted and deployed IPv4 implementation of TCP/IP. This update addresses the vulnerability in the IPv6 implementation.

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.

Revisions:
•

V1.0 (October 10, 2006): Bulletin published.