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SecurityvulnsSECURITYVULNS:DOC:16961

HistoryMay 08, 2007 - 12:00 a.m.

Microsoft Security Bulletin MS07-026 Vulnerabilities in Microsoft Exchange Could Allow Remote Code Execution (931832)

2007-05-0800:00:00

vulners.com

Microsoft Security Bulletin MS07-026
Vulnerabilities in Microsoft Exchange Could Allow Remote Code Execution (931832)
Published: May 8, 2007

Version: 1.0
Summary

Who Should Read this Document: Customers who use Microsoft Exchange Server

Impact of Vulnerability: Remote Code Execution

Maximum Severity Rating: Critical

Recommendation: Customers should apply the update immediately

Security Update Replacement: This bulletin replaces two prior security updates. See the Frequently Asked Questions (FAQ) section of this bulletin for details.

Tested Software and Security Update Download Locations:

Affected Software:
•

Microsoft Exchange 2000 Server Service Pack 3 with the Exchange 2000 Post-Service Pack 3 Update Rollup of August 2004 — Download the update (KB931832)
•

Microsoft Exchange Server 2003 Service Pack 1 — Download the update (KB931832)
•

Microsoft Exchange Server 2003 Service Pack 2 — Download the update (KB931832)
•

Microsoft Exchange Server 2007 — Download the update (KB935490)

The software in this list has been tested to determine whether the versions are affected. Other versions are either past their support life cycle or are not affected. To determine the support life cycle for your product and version, visit the Microsoft Support Lifecycle Web site.
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General Information

Executive Summary

Executive Summary:

This update resolves several newly discovered, privately reported vulnerabilities. Each vulnerability is documented in its own subsection in the Vulnerability Details section of this bulletin.

An attacker who successfully exploited the most severe of these vulnerabilities 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.

We recommend that customers apply the update immediately.

Severity Ratings and Vulnerability Identifiers:
Vulnerability Identifiers Impact of Vulnerability Microsoft Exchange 2000 Server Service Pack 3 Microsoft Exchange Server 2003 Service Pack 1 and Microsoft Exchange Server 2003 Service Pack 2 Microsoft Exchange Server 2007

Outlook Web Access Script Injection Vulnerability - CVE-2007-0220

Information Disclosure

Important

None

Malformed iCal Vulnerability - CVE-2007-0039

Denial of Service

Important

MIME Decoding Vulnerability - CVE-2007-0213

Remote Code Execution

Critical

IMAP Literal Processing Vulnerability - CVE-2007-0221

Denial of Service

Important

None

Aggregate Severity of All Vulnerabilities

Critical

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

What is different about the Microsoft Exchange Server2007 update from Microsoft Exchange Server 2000 and Microsoft Exchange Server 2003?
With the release of Microsoft Exchange 2007, Microsoft Exchange is moving to a new servicing model. For better understanding of the Microsoft Exchange servicing model, please see the Exchange 2007 product documentation. For questions regarding the new Exchange servicing model, please contact Microsoft Product Support Services.

What updates does this release replace?
This security update replaces two prior security updates. The security bulletin IDs and affected operating systems are listed in the following table.
Bulletin ID Microsoft Exchange 2000 Server Service Pack 3 Microsoft Exchange Server 2003 Service Pack 1 and Microsoft Exchange Server 2003 Service Pack 2 Microsoft Exchange Server 2007

MS06-019

Replaced

Not Applicable

MS06-029

Replaced

Not Applicable

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 2.0.1

Microsoft Exchange 2000 Server Service Pack 3

Yes

Microsoft Exchange Server 2003 Service Pack 1 and Microsoft Exchange Server 2003 Service Pack 2

Yes

Microsoft Exchange Server 2007

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: Summary list of monthly detection and deployment guidance articles.

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 Exchange 2000 Server Service Pack 3

Yes

Microsoft Exchange Server 2003 Service Pack 1 and Microsoft Exchange Server 2003 Service Pack 2

Yes

Microsoft Exchange Server 2007

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 SMS 2.0, the SMS SUS Feature Pack, which includes the Security Update Inventory Tool (SUIT), can be used by SMS to detect security updates. SMS SUIT uses the MBSA 1.2.1 engine for detection. For more information about SUIT, visit the following Microsoft Web site. For more information about the limitations of SUIT, 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 (ITMU) 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 ITMU, 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: Summary list of monthly detection and deployment guidance articles.
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Vulnerability Details

Outlook Web Access Script Injection Vulnerability - CVE-2007-0220:

An information disclosure vulnerability exists in Microsoft Exchange in the way that Outlook Web Access (OWA) handles script-based attachments. An attached script could spoof content, disclose information, or take any action that the user could take within the context of the OWA session.

Mitigating Factors for Outlook Web Access Script Injection Vulnerability - CVE-2007-0220:
•

The vulnerability could not be exploited automatically through e-mail. For an attack to be successful an attacker must e-mail a specially crafted file to a user and convince the user to open the file within an authenticated OWA session.
•

Microsoft Exchange Server 2007 is not affected by this vulnerability.
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Workarounds for Outlook Web Access Script Injection Vulnerability - CVE-2007-0220:

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.
•

Disable Outlook Web Access (OWA) on a computer running Exchange Server.

Disabling Outlook Web Access helps protect the affected system from attempts to exploit this vulnerability. To disable Outlook Web Access, follow these steps:

Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.

Expand Servers, expand Server, expand Protocols, and then expand HTTP.

Right-click Exchange Virtual Server, and then click Stop.

Note A red cross will appear over the Exchange Virtual Server icon, indicating it has been stopped. From now on, users will see a The Page Cannot Be Displayed error message when they try to access their e-mail through OWA.

Impact of workaround: This workaround prevents users from accessing their mailboxes through Outlook Web Access (OWA), Outlook Mobile Access (OMA) and Exchange Server ActiveSync.
•

Block HTML Attachment as Level2 Type in Outlook Web Access (OWA).

Set Outlook Web Access to save HTML attachments locally before they are opened. This enables Internet Explorer to check for active content and warn the user before opening the attachment.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use the Registry Editor at your own risk.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWEB\OWA

Update "Level2MIMETypes" to include ”text/html”

Update “Level2FileTypes” to include ”htm,html”

You can apply this .reg file to individual systems by double-clicking it. You can also apply it across domains by using Group Policy. For more information about Group Policy, visit the following Microsoft Web sites:

Group Policy collection

What is Group Policy Object Editor?

Core Group Policy tools and settings

Note You must restart Internet Explorer for your changes to take effect.

Impact of workaround: The Outlook Web Access client has to save the HTML attachment locally before it could be opened.
•

Block HTML Attachment as Level1 Type in Outlook Web Access (OWA).

Set Outlook Web Access to block the ability to save HTML attachments locally.

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWEB\OWA

Update "Level1MIMETypes" to include ”text/html”

Update “Level1FileTypes” to include ”htm,html”

Group Policy collection

What is Group Policy Object Editor?

Core Group Policy tools and settings

Note You must restart Internet Explorer for your changes to take effect.

Impact of workaround: The Outlook Web Access client will not be able to retrieve HTML attachment. Access is totally blocked.
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FAQ for Outlook Web Access Script Injection Vulnerability - CVE-2007-0220:

What is the scope of the vulnerability?
A script injection vulnerability exists that could allow an attacker to run a script supplied by the attacker. If this script were run, it would run in the security context of the OWA user on the client system. The script could take any action on the user's computer that the Web site was authorized to take. These actions could include monitoring the user’s 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?
An incorrectly handled UTF character set label in Outlook Web Access could allow unauthorized scripts to run.

What is Outlook Web Access?
Microsoft Outlook Web Access (OWA) is a service of Exchange Server. By using OWA, a server that is running Exchange Server can also function as a Web site that lets authorized users read and send e-mail, manage their calendar, and perform other e-mail functions over the Internet.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could gain access to the Outlook Web Access session in the security context of the exploited user. The attacker could then change, delete, forward e-mail, or perform other actions on behalf of the logged on user.

How could an attacker exploit the vulnerability?
An attacker could exploit the vulnerability by e-mailing a specially-crafted file to the user and by persuading the user to open the file within an authenticated OWA session.

What systems are primarily at risk from the vulnerability?
Users who are using Microsoft Exchange Outlook Web Access to read e-mail are primarily at risk.

What does the update do?
The update removes the vulnerability by changing the way that Outlook Web Access handles UTF encoded attachments.

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.
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Malformed iCal Vulnerability - CVE-2007-0039:

A denial of service vulnerability exists in Microsoft Exchange Server because of the way that it handles calendar content requests. An attacker could exploit the vulnerability by sending an e-mail message with specially crafted iCal file to a Microsoft Exchange Server user account. An attacker successfully exploiting this vulnerability could cause the mail service to stop responding.

Mitigating Factors for Malformed iCal Vulnerability - CVE-2007-0039:

We have not identified any mitigations for this vulnerability.
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Workarounds for Malformed iCal Vulnerability - CVE-2007-0039:

Require authentication for connections to a server that is running Microsoft Exchange Server for all client and message transport protocols

Requiring authentication for all connections made to the Exchange Server computer will help protect against anonymous attacks. This will not protect against an attack from a user who can successfully authenticate.

Impact of workaround: Anonymous communication from clients through IMAP, POP3, HTTP, LDAP, SMTP, and NNTP will no longer be possible. Server to server anonymous communication through RPC, X.400, foreign gateway, and third-party connector protocols will also no longer be possible. In default configurations of Exchange Server, authenticated access is required for all protocols except SMTP. If all text/calendar MIME type message parts and the meeting.ics file are blocked, anonymous SMTP connections could still be accepted.
•

Block iCal on Microsoft Exchange Server to help protect against attempts to exploit this vulnerability through SMTP e-mail

Systems can be configured to block certain types of files from being received as e-mail attachments. Meeting requests, typically used in Outlook, contain a file attachment that stores the meeting information. This file attachment is usually named meeting.ics. Blocking this file, and blocking the calendar MIME type, could help protect Exchange Servers and other affected programs from attempts to exploit this vulnerability if customers cannot install the available security update. To help protect an Exchange Server computer from attacks through SMTP, block the .ics files and all text/calendar MIME type content before it reaches the Exchange Server computer.

Note Exchange supports other messaging protocols, such as X.400, that these workarounds do not protect. We recommend that administrators require authentication on all other client and message transport protocols to help prevent attacks using these protocols.

Note Filtering only for attachments that have the file name meeting.ics may not be sufficient to help protect your system. A specially crafted file attachment could be given another file name that could then be processed by the Exchange Server computer. To help protect against specially crafted e-mail messages, block all text/calendar MIME type content.

There are many ways to block the meeting.ics file and other calendar content. Here are some suggestions:
•

You can use ISA Server 2000 SMTP Message Screener to block all file attachments or to block only the meeting.ics file. Blocking all file attachments provides the most protection for this issue if you use ISA Server 2000 because ISA Server 2000 does not support blocking content based on MIME content types. For more information, see Microsoft Knowledge Base Article 315132.
•

You can use ISA Server 2000 SMTP Filter to block all file attachments or to block only the meeting.ics file. Blocking all file attachments provides the most protection for this issue if you use ISA Server 2000 because ISA Server 2000 does not support blocking content based on MIME content types. For more information, see Microsoft Knowledge Base Article 320703.
•

You can use ISA Server 2004 SMTP Filter and Message Screener block all file attachments or just the meeting.ics file. Blocking all file attachments provides the most protection for this issue if you use ISA Server 2004 because ISA Server 2004 does not support blocking content based on MIME content types. For more information, see Microsoft Knowledge Base Article 888709.
•

You can use third-party e-mail filters to block all text/calendar MIME type content before it is sent to the Exchange Server computer or to a vulnerable application.

Impact of workaround: If calendar attachments are blocked, meeting requests will not be received correctly. In some cases, users could receive blank e-mail messages instead of the original meeting request. In other cases, users may not receive meeting requests at all. Perform this workaround only if you cannot install the available security update or if a security update is not publicly available for your configuration.
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FAQ for Malformed iCal Vulnerability - CVE-2007-0039:

What is the scope of the vulnerability?
This is a denial of service vulnerability. An attacker who successfully exploited this vulnerability could cause the e-mail service to stop responding on a Microsoft Exchange Server. During that time, the Exchange Server cannot respond to user requests to access, send, or receive e-mail. The Microsoft Exchange Information Store service must be restarted to regain its functionality.

What causes the vulnerability?
EXCDO functionality provided with Exchange Server does not properly process certain iCal properties provided in email messages.

What is EXCDO?
Exchange Collaboration Data Objects (EXCDO) is an interface that allows for certain types of information to be processed in the Exchange store.

What is iCAL?
Internet Calendar (iCAL) is a MIME content type used by Microsoft Exchange Server and e-mail clients when sending and exchanging information related to calendars and scheduling.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could cause the e-mail service to stop responding on a Microsoft Exchange Server. During that time, the Exchange Server cannot respond to user requests to access, send, or receive e-mail. The Microsoft Exchange Information Store service must be restarted to regain its functionality.

How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by creating a specially crafted iCal file and sending an e-mail message with the file to a user account connected configured for a Microsoft Exchange Server. An attacker successfully exploiting this vulnerability could cause the mail service to stop responding.

What systems are primarily at risk from the vulnerability?
Microsoft Exchange Servers are primarily at risk from this vulnerability.

What does the update do?
The update removes the vulnerability by modifying the way Exchange Server processes messages with iCal properties.

MIME Decoding Vulnerability - CVE-2007-0213:

A remote code execution vulnerability exists in Microsoft Exchange Server because of the way that it decodes specially crafted e-mail messages. An attacker could exploit the vulnerability by sending a specially crafted e-mail to a Microsoft Exchange Server user account. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

Mitigating Factors for MIME Decoding Vulnerability - CVE-2007-0213:

We have not identified any mitigations for this vulnerability.
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Workarounds for MIME Decoding Vulnerability - CVE-2007-0213:

Microsoft has tested the following workarounds. While these workarounds will not correct the underlying vulnerability, they will help to block known attack vectors. When a workaround reduces functionality, it is identified in the following section.
•

Require authentication for connections to a server that is running Microsoft Exchange Server for all client and message transport protocols.

Requiring authentication for all connections made to the Exchange Server computer will help protect against anonymous attacks. This will not protect against an attack from a malicious user who can successfully authenticate.

FAQ for MIME Decoding Vulnerability - CVE-2007-0213:

What is the scope of the vulnerability?
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability could remotely 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?
Microsoft Exchange incorrectly handles the decoding of specially crafted, base64 encoded content.

What is MIME?
MIME stands for Multipurpose Internet Mail Extensions, a protocol for defining file attachments for the Web.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

How could an attacker exploit the vulnerability?
An attacker could exploit the vulnerability by sending a specially crafted e-mail to a Microsoft Exchange Server user account. An attacker who successfully exploited this vulnerability could take complete control of an affected system.

What systems are primarily at risk from the vulnerability?
Microsoft Exchange Servers are primarily at risk from this vulnerability.

What does the update do?
The update removes the vulnerability by modifying the way that Exchange Server handles base64-encoded messages.

IMAP Literal Processing Vulnerability - CVE-2007-0221:

A denial of service vulnerability exists in Microsoft Exchange Server because of the way that it handles invalid IMAP requests. An attacker could exploit the vulnerability by sending a specially crafted IMAP command to a Microsoft Exchange Server configured as an IMAP server. An attacker successfully exploiting this vulnerability could cause the mail service to stop responding.

Mitigating Factors for IMAP Literal Processing Vulnerability - CVE-2007-0221:
•

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.
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Workarounds for IMAP Literal Processing Vulnerability - CVE-2007-0221:

Block the following at the firewall:
•

TCP port 143

This port is used to initiate a connection with IMAP. Blocking it at the firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability.
•

Disable the IMAP service

Disabling the IMAP service will help protect the affected system from attempts to exploit this vulnerability. To disable the IMAP service, follow these steps:

Click Start, and then click Control Panel. Alternatively, point to Settings, and then click Control Panel.

Double-click Administrative Tools.

Double-click Services.

Double-click IMAP4.

In the Startup type list, click Disabled.

Click Stop, and then click OK.

You can also stop and disable the IMAP service by using the following command at the command prompt:

sc stop IMAP4svc
sc config IMAP4svc start= disabled

Impact of workaround: If you disable the IMAP service, you turn off IMAP functionality for IMAP clients.
•

Stop the IMAP virtual server

Stopping the IMAP virtual server will help protect the affected system from attempts to exploit this vulnerability. To stop the IMAP virtual server, follow these steps:

Click Start, point to All Programs, point to Microsoft Exchange, and then click System Manager.

Expand Servers, expand Server, expand Protocols, and then expand IMAP4.

Right-click IMAP4 Virtual Server and then click Stop.

Impact of workaround: If you disable the IMAP virtual server, you turn off IMAP functionality for IMAP clients.
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FAQ for Vulnerabilities in IMAP Literal Processing Vulnerability - CVE-2007-0221:

What is the scope of the vulnerability?
This is a denial of service vulnerability. An attacker who successfully exploited this vulnerability could cause the e-mail service to stop responding on a Microsoft Exchange Server. During that time, the Exchange Server cannot respond to user requests to access, send, or receive e-mail. The IIS Admin Service service must be restarted to regain its functionality.

What causes the vulnerability?
The vulnerability is caused by incorrect handling of a command in the IMAP service.

What is IMAP?
IMAP stands for Internet Message Access Protocol. IMAP is an e-mail protocol that Exchange and other e-mail programs use to exchange messages. IMAP allows users to perform tasks including folder creation, message searching, and other e-mail tasks.

What might an attacker use the vulnerability to do?
An attacker who successfully exploited this vulnerability could cause the e-mail service to stop responding on a Microsoft Exchange Server. During that time, the Exchange Server cannot respond to user requests to access, send, or receive e-mail. The IIS Admin Service service must be restarted to regain its functionality.

How could an attacker exploit the vulnerability?
An attacker could try to exploit the vulnerability by sending a specially crafted IMAP command to a Microsoft Exchange Server configured as an IMAP server. An attacker successfully exploiting this vulnerability could cause the mail service to stop responding.

What systems are primarily at risk from the vulnerability?
While the security update is intended for any affected and supported Microsoft Exchange Server, servers hosting IMAP services are primarily at risk from this vulnerability.

What does the update do?
The update removes the vulnerability by modifying the way that Microsoft Exchange Server validates IMAP commands.

Acknowledgments

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

Martijn Brinkers of Izecom for reporting the Outlook Web Access Script Injection Vulnerability (CVE-2007-0220).
•

Alexander Sotirov of Determina Security Research for reporting the Malformed iCal Vulnerability Vulnerability (CVE-2007-0039).
•

Joxean Koret, working with the iDefense Vulnerability Contributor Program, for reporting the IMAP Literal Processing Vulnerability (CVE-2007-0221).

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 (May 8, 2007): Bulletin published.