Microsoft Security Bulletin MS09-031 - Important Vulnerability in Microsoft ISA Server 2006 Could Cause Elevation of Privilege (970953)

Microsoft Security Bulletin MS09-031 - Important
Vulnerability in Microsoft ISA Server 2006 Could Cause Elevation of Privilege (970953)
Published: July 14, 2009

Version: 1.0
General Information
Executive Summary

This security update resolves a privately reported vulnerability in Microsoft Internet Security and Acceleration (ISA) Server 2006. The vulnerability could allow elevation of privilege if an attacker successfully impersonates an administrative user account for an ISA server that is configured for Radius One Time Password (OTP) authentication and authentication delegation with Kerberos Constrained Delegation.

This security update is rated Important for Microsoft Internet Security and Acceleration (ISA) Server 2006. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by rejecting requests that cannot be authenticated using Radius OTP. For more information about the vulnerability, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Microsoft recommends that customers apply the update at the earliest opportunity.

Known Issues. Microsoft Knowledge Base Article 970953 documents the currently known issues that customers may experience when installing this security update. The article also documents recommended solutions for these issues. When currently known issues and recommended solutions pertain only to specific releases of this software, this article provides links to further articles.
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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
Software Maximum Security Impact Aggregate Severity Rating Bulletins Replaced by this Update

Microsoft Internet Security and Acceleration Server 2006
(KB970811)

Elevation of Privilege

Important

None

Microsoft Internet Security and Acceleration Server 2006 Supportability Update
(KB970811)

Elevation of Privilege

Important

None

Microsoft Internet Security and Acceleration Server 2006 Service Pack 1
(KB971143)

Elevation of Privilege

Important

None

Non-Affected Software
Software

Microsoft Forefront Threat Management Gateway, Medium Business Edition

Microsoft Internet Security and Acceleration Server 2000 Enterprise Edition Service Pack 2

Microsoft Internet Security and Acceleration Server 2000 Standard Edition Service Pack 2

Microsoft Internet Security and Acceleration Server 2004 Enterprise Edition Service Pack 3

Microsoft Internet Security and Acceleration Server 2004 Standard Edition Service Pack 3
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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.

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 July bulletin summary. For more information, see Microsoft Exploitability Index.
Vulnerability Severity Rating and Maximum Security Impact by Affected Software
Affected Software Radius OTP Bypass Vulnerability - CVE-2009-1135 Aggregate Severity Rating

Microsoft Internet Security and Acceleration Server 2006

Important
Elevation of Privilege

Important

Microsoft Internet Security and Acceleration Server 2006 Supportability Update

Important
Elevation of Privilege

Important

Microsoft Internet Security and Acceleration Server 2006 Service Pack 1

Important
Elevation of Privilege

Important
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Radius OTP Bypass Vulnerability - CVE-2009-1135

An elevation of privilege vulnerability exists in ISA Server 2006 authentication when configured with Radius OTP. The vulnerability could allow an unauthenticated user access to any Web published resource. With knowledge of administrator account usernames, an attacker who successfully exploited this vulnerability could take complete control of systems relying on the ISA Server 2006 Web publishing rules for authentication. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2009-1135.

Mitigating Factors for Radius OTP Bypass Vulnerability - CVE-2009-1135

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:
•

If the ISA server is not set up for Radius One Time Password (OTP) authentication and authentication delegation with Kerberos Constrained Delegation, then it is not vulnerable.
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Workarounds for Radius OTP Bypass Vulnerability - CVE-2009-1135

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 fallback to Basic authentication for ISA Forms-Based authentication together with Radius OTP

For customers running the original release version of Microsoft Internet Security and Acceleration Server 2006, install the hotfix available from Microsoft Knowledge Base Article 938966. Customers running Microsoft Internet Security and Acceleration Server 2006 Supportability Update and Microsoft Internet Security and Acceleration Server 2006 Service Pack 1 do not need to apply the hotfix.

Run the Microsoft Visual Basic script available from the Post-hotfix installation information section of Microsoft Knowledge Base Article 938966, according to the instructions in the article.

Impact of workaround. ISA server will not allow basic authentication from clients served by that Web Listener.

How to undo the workaround.

Edit the Microsoft Visual Basic script available from the Post-hotfix installation information section of Microsoft Knowledge Base Article 938966 to revise "Const SE_VPS_VALUE = true" to "Const SE_VPS_VALUE = false."

Save the script, and then run it.
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FAQ for Radius OTP Bypass Vulnerability - CVE-2009-1135

What is the scope of the vulnerability?
An attacker who successfully exploited this vulnerability could gain access to published resources in the context of a valid user without having to authenticate with the ISA server.

What causes the vulnerability?
ISA Server 2006 attempts to authenticate requests using the HTTP-Basic method.

What is Radius One Time Password (OTP) authentication?
For information on how ISA Server 2006 is used in conjunction with Radius One Time Password (OTP) authentication, see the TechNet article, Authentication in ISA Server 2006.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability may be able to impersonate user accounts. If an attacker is able to successfully impersonate a user account, they may have access to resources the impersonated user has. If an attacker is impersonating an administrative account, the attacker might be able to install programs; view, change, or delete data; or create new accounts with full user rights on systems behind the ISA Server 2006 security boundary.

How could an attacker exploit the vulnerability?
To exploit this vulnerability, an attacker would only have to know the username that the attacker is intending to impersonate. An attacker could then use that username and attempt to access a resource that is segregated from the network by an ISA Server 2006 system.

What systems are primarily at risk from the vulnerability?
ISA Server 2006 systems configured with Forms-Based authentication validated against a Radius OTP server and using Kerberos Constrained Delegation in the Web publishing rule are primarily at risk from this vulnerability.

What does the update do?
ISA Server 2006 will now reject requests that cannot be authenticated using Radius OTP.

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.

Other Information
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.
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Support
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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.

Revisions
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V1.0 (July 14, 2009): Bulletin published.