Microsoft Security Bulletin MS06-056 Vulnerability in ASP.NET 2.0 Could Allow Information Disclosure (922770)

Microsoft Security Bulletin MS06-056
Vulnerability in ASP.NET 2.0 Could Allow Information Disclosure (922770)
Published: October 10, 2006

Version: 1.0
Summary

Who Should Read this Document: Customers who use Microsoft Windows .NET Framework 2.0

Impact of Vulnerability: Information Disclosure

Maximum Severity Rating: Moderate

Recommendation: Customers should consider applying the security update

Security Update Replacement: None

Caveats: None

Tested Software and Security Update Download Locations:

Affected Software:

Microsoft .NET Framework 2.0 for the following operating system versions: Download the update
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Microsoft Windows 2000 Service Pack 4
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Microsoft Windows XP Service Pack 1 or Windows XP Service Pack 2
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Microsoft Windows XP Professional x64 Edition
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Microsoft Windows XP Tablet PC Edition
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Microsoft Windows XP Media Center Edition
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Microsoft Windows Server 2003 or Microsoft Windows Server 2003 Service Pack 1
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Microsoft Windows Server 2003 for Itanium-based Systems or Windows Server 2003 with SP1 for Itanium-based Systems
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Microsoft Windows Server 2003 x64 Edition

Tested Microsoft Windows Components:

Affected Components:
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Microsoft .NET Framework 2.0

Non-Affected Components:
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Microsoft .NET Framework 1.0
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Microsoft .NET Framework 1.1

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 newly discovered, privately reported vulnerability. The vulnerability is documented in the "Vulnerability Details" section of this bulletin.

The vulnerability could allow an attacker to gain unauthorized access to information. Note that this vulnerability would not allow an attacker to execute code to elevate their user rights directly, but it could be used to acquire information that could be used to further compromise the affected system.

We recommend that customers consider applying the security update.

Severity Ratings and Vulnerability Identifiers:
Vulnerability Identifiers Impact of Vulnerability .NET Framework 2.0

.NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436

Information Disclosure

Moderate
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Frequently Asked Questions (FAQ) Related to This Security Update

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 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 Enterprise Update Scan Tool (EST) MBSA 2.0

.NET Framework 2.0

No

Yes

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.

What is the Enterprise Update Scan Tool (EST)?
As part of an ongoing commitment to provide detection tools for bulletin-class security updates, Microsoft delivers a stand-alone detection tool whenever the Microsoft Baseline Security Analyzer (MBSA) and the Office Detection Tool (ODT) cannot detect whether the update is required for an MSRC release cycle. This stand-alone tool is called the Enterprise Update Scan Tool (EST) and is designed for enterprise administrators. When a version of the Enterprise Update Scan Tool is created for a specific bulletin, customers can run the tool from a command-line interface (CLI) and view the results of the XML output file. To help customers better utilize the tool, detailed documentation will be provided with the tool. There is also a version of the tool that offers an integrated experience for SMS administrators.

Can I use a version of the Enterprise Update Scan Tool (EST) to determine whether this update is required?
Yes. Microsoft has created a version of EST that will determine if you have to apply this update. For download links and more information about the version of the EST that is being released this month, see Microsoft Knowledge Base Article 894193. SMS customers should review the FAQ, “Can I use Systems Management Server (SMS) to determine whether this update is required?" for more information about SMS and EST.

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

.NET Framework 2.0

Yes (with the EST)

Yes

SMS uses MBSA for detection. Therefore, SMS has the same limitation that is listed earlier in this bulletin related to programs that MBSA does not detect.

For SMS 2.0, the SMS SUS Feature Pack, which includes the Security Update Inventory Tool, can be used by SMS to detect security updates. SMS SUIT uses the MBSA 1.2.1 engine for detection. For more information about the Security Update Inventory Tool, visit the following Microsoft Web site. For more information about the limitations of the Security Update Inventory Tool, see Microsoft Knowledge Base Article 306460. The SMS SUS Feature Pack also includes the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

For SMS 2003, the SMS 2003 Inventory Tool for Microsoft Updates can be used by SMS to detect security updates that are offered by Microsoft Update and that are supported by Windows Server Update Services. For more information about the SMS 2003 Inventory Tool for Microsoft Updates, visit the following Microsoft Web site. SMS 2003 can also use the Microsoft Office Inventory Tool to detect required updates for Microsoft Office applications.

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

.NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436:

A cross-site scripting vulnerability exists in a server running a vulnerable version of the .Net Framework 2.0 that could inject a client side script in the user's browser. The script could spoof content, disclose information, or take any action that the user could take on the affected web site. Attempts to exploit this vulnerability require user interaction.

Mitigating Factors for .NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436:
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In a Web-based attack scenario a compromised Web server an attacker could inject a client side script in the user's browser. The script could spoof content, disclose information, or take any action that the user could take on the affected web site. Attempts to exploit this vulnerability would require user interaction.
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By default, .NET Framework 2.0 controls do not set the AutoPostBack property to “true”.
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Workarounds for .NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436:

Microsoft has tested the following workarounds. Although these workarounds will not correct the underlying vulnerability, they help block known attack vectors. When a workaround reduces functionality, it is identified in the following section.
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On computers running .NET Framework 2.0, do not set the AutoPostBack property for controls on a page to “true”:
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On computers running .NET Framework 2.0 AutoPostBack is a property of controls on a WebForm. By default the AutoPostBack property is set to false. For more information, see Knowledge Base Article 328923.
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FAQ for .NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436:

What is the scope of the vulnerability?
A cross-site scripting vulnerability may exist in a server running a vulnerable version of the .Net Framework 2.0 that could inject a client side script in the user's browser. The vulnerability is within ASP.NET controls that set the AutoPostBack property to “true”. In a Web-based attack scenario a compromised Web site could accept or host user-provided content or advertisements which could contain specially crafted content that could exploit this vulnerability.

The script could take any action on the user's behalf that the Web site is authorized to take. This could include monitoring the Web session and forwarding information to a third party, running other code on the user's system, and reading or writing cookies.

What causes the vulnerability?
A cross-site scripting (XSS) vulnerability results from the way that .NET Framework 2.0 validates the value of an HTTP request.

What is ASP.NET?
ASP.NET is a collection of technologies within the.NET Framework that enable developers to build Web applications and XML Web Services.

Unlike traditional Web pages, which use a combination of static HTML and scripting, ASP.NET uses compiled, event-driven pages. This enables developers to build Web-based applications with the same richness and functionality usually associated with applications built in languages such as Visual Basic or Visual C++. Because ASP.NET is a Web-based application environment, it requires an underlying Web server to provide basic HTTP functionality. For this reason, ASP.NET runs on top of Internet Information Services (IIS) 5.0 on Windows 2000, IIS 5.1 on Windows XP, and IIS 6.0 on Windows Server 2003.

What is AutoPostBack?
AutoPostBack is a property supported by controls in a form. Forms using a control that supports this property can set the value of this property to true (the default value is false) which results in control posting back to the server each time a user interacts with the control.

What is cross-site scripting?
Cross-site scripting (XSS) is a class of security vulnerability that can enable an attacker to "inject" script code into a user's session with a Website. The vulnerability can affect Web servers that dynamically generate HTML pages. If these servers embed browser input in the dynamic pages that they send back to the browser, these servers can be manipulated to include maliciously supplied content in the dynamic pages. This can allow malicious script to be executed. Web browsers may perpetuate this problem through their assumptions of "trusted" sites and their use of cookies to maintain persistent state with the Websites that they frequent. An XSS attack does not modify Website content. Instead, it inserts new, malicious script that can execute at the browser in the context that is associated with a trusted server.

How does cross-site scripting work?
Web pages contain text and HTML markup. Text and HTML markup are generated by the server and are interpreted by the client. If untrusted content is introduced into a dynamic page, neither the server nor the client has sufficient information to recognize that this injection has occurred and to take protective measures.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability on a server running a vulnerable version of the .Net Framework 2.0, could inject a client side script in the user's browser. The script could spoof content, disclose information, or take any action that the user could take on the affected web site. Attempts to exploit this vulnerability would require user interaction.

Who could exploit the vulnerability?
In an e-mail attack scenario an attacker could exploit the vulnerability by sending a specially crafted e-mail message to a user of a server that is running an affected software application. The attacker could then persuade the user to click a link in the e-mail message.

In a Web-based attack scenario a compromised Web an attacker could inject a client side script in the user's browser. The script could spoof content, disclose information, or take any action that the user could take on the affected web site. Attempts to exploit this vulnerability would require user interaction.

What systems are primarily at risk from the vulnerability?
Internet facing systems are primarily at risk from this vulnerability. In addition, internal Web sites that use ASP.NET to host sensitive data can be 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.

What does the update do?
The update removes the vulnerability by modifying the way that .ASP.NET validates the value of a HTTP request.

When this security bulletin was issued, had this vulnerability been publicly disclosed?
No. Microsoft received information about this vulnerability through responsible disclosure. Microsoft had not received any information to indicate that this vulnerability had been publicly disclosed when this security bulletin was originally issued.

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.

Acknowledgments

Microsoft thanks the following for working with us to help protect customers:
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Jaswinder Hayre for reporting the .NET Framework 2.0 Cross-Site Scripting Vulnerability - CVE-2006-3436.

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