Microsoft Security Bulletin MS12-039 - Important

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:

• An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

Microsoft has not identified any workarounds for this vulnerability.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability.

What causes the vulnerability? 
The vulnerability is caused when specially crafted True Type Font (TTF) files are incorrectly handled.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker 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. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability? 
An attacker could share content that contains specially crafted TrueType fonts. The vulnerability could be exploited when a user views the shared content that contains specially crafted TrueType fonts.

What systems are primarily at risk from the vulnerability? 
Workstations and terminal servers are primarily at risk. Servers could be at more risk if administrators allow users to log on to servers and to run programs. However, best practices strongly discourage allowing this.

What does the update do? 
The update addresses the vulnerability by correcting how specially crafted TTF files are handled.

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-2011-3402.

When this security bulletin was issued, had Microsoft received any reports that this vulnerability was being exploited? 
Although this vulnerability has previously been exploited through limited, targeted attacks, the exploited attack vectors were addressed in MS11-087, Vulnerability in Windows Kernel-Mode Drivers Could Allow Remote Code Execution (2639417). Microsoft had not received any information to indicate that the attack vectors addressed in this bulletin had been publicly used to attack customers when this security bulletin was originally issued.

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:

• An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

Microsoft has not identified any workarounds for this vulnerability.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability.

What causes the vulnerability? 
The vulnerability is caused when specially crafted True Type Font (TTF) files are incorrectly handled.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker 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. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability? 
An attacker could share content that contains specially crafted TrueType fonts. The vulnerability could be exploited when a user views the shared content that contains specially crafted TrueType fonts.

What systems are primarily at risk from the vulnerability? 
Workstations are primarily at risk for this vulnerability.

What does the update do? 
The update addresses the vulnerability by correcting how specially crafted TTF files are handled.

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

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:

• For an attack to be successful, a user must visit an untrusted remote file system location or WebDAV share and open a legitimate file (such as an .ocsmeet file) from this location that is then loaded by a vulnerable application.
• The file sharing protocol, Server Message Block (SMB), is often disabled on the perimeter firewall. This limits the potential attack vectors for this vulnerability.
• An attacker who successfully exploited this vulnerability could gain the same user rights as the logged-on user. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

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 loading of libraries from WebDAV and remote network shares

  Note See Microsoft Knowledge Base Article 2264107 to deploy a workaround tool that allows customers to disable the loading of libraries from remote network or WebDAV shares. This tool can be configured to disallow insecure loading on a per-application or a global system basis.

  Customers who are informed by their vendor of an application being vulnerable can use this tool to help protect against attempts to exploit this issue.

  Note See Microsoft Knowledge Base Article 2264107 to use the automated Microsoft Fix it solution to deploy the registry key to block the loading of libraries for SMB and WebDAV shares. Note that this Fix it solution does require you to install the workaround tool also described in Microsoft Knowledge Base Article 2264107 first. This Fix it solution only deploys the registry key and requires the workaround tool in order to be effective. We recommend that administrators review the KB article closely prior to deploying this Fix it solution.

• Disable the WebClient service

  Disabling the WebClient service helps protect affected systems from attempts to exploit this vulnerability by blocking the most likely remote attack vector through the Web Distributed Authoring and Versioning (WebDAV) client service. After applying this workaround it is still possible for remote attackers who successfully exploit this vulnerability to cause the system to run programs located on the targeted user's computer or the Local Area Network (LAN), but users will be prompted for confirmation before opening arbitrary programs from the Internet.

  To disable the WebClient Service, follow these steps:

  1. Click Start, click Run, type Services.msc and then click OK.
  2. Right-click WebClient service and select Properties.
  3. Change the Startup type to Disabled. If the service is running, click Stop.
  4. Click OK and exit the management application.

  Impact of workaround. When the WebClient service is disabled, Web Distributed Authoring and Versioning (WebDAV) requests are not transmitted. In addition, any services that explicitly depend on the Web Client service will not start, and an error message will be logged in the System log. For example, WebDAV shares will be inaccessible from the client computer.

  How to undo the workaround.

  To re-enable the WebClient Service, follow these steps:

  1. Click Start, click Run, type Services.msc and then click OK.
  2. Right-click WebClient service and select Properties.
  3. Change the Startup type to Automatic. If the service is not running, click Start.
  4. Click OK and exit the management application.
• Block TCP ports 139 and 445 at the firewall

  These ports are used to initiate a connection with the affected component. Blocking TCP ports 139 and 445 at the firewall will help protect systems that are behind that firewall from attempts to exploit this vulnerability. Microsoft recommends that you block all unsolicited inbound communication from the Internet to help prevent attacks that may use other ports. For more information about ports, see the TechNet article, TCP and UDP Port Assignments.

  Impact of workaround. Several Windows services use the affected ports. Blocking connectivity to the ports may cause various applications or services to not function. Some of the applications or services that could be impacted are listed below:

  • Applications that use SMB (CIFS)
  • Applications that use mailslots or named pipes (RPC over SMB)
  • Server (File and Print Sharing)
  • Group Policy
  • Net Logon
  • Distributed File System (DFS)
  • Terminal Server Licensing
  • Print Spooler
  • Computer Browser
  • Remote Procedure Call Locator
  • Fax Service
  • Indexing Service
  • Performance Logs and Alerts
  • Systems Management Server
  • License Logging Service

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

What is the scope of the vulnerability? 
This is a remote code execution vulnerability.

What causes the vulnerability? 
The vulnerability is caused when Microsoft Lync incorrectly restricts the path used for loading external libraries.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could run arbitrary code as the current user. If the current user is logged-on with administrative user rights, an attacker 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. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.

How could an attacker exploit the vulnerability? 
An attacker could convince a user to open a legitimate Microsoft Lync related file (such as an .ocsmeet file) that is located in the same network directory as a specially crafted dynamic link library (DLL) file. Then, while opening the legitimate file, Microsoft Lync could attempt to load the DLL file and execute any code it contained.

In an email attack scenario, an attacker could exploit the vulnerability by sending a legitimate Microsoft Lync-related file (such as an .ocsmeet file) to a user, and convincing the user to place the attachment into a directory that contains a specially crafted DLL file and to open the legitimate file. Then, while opening the legitimate file, Microsoft Lync could attempt to load the DLL file and execute any code it contained.

In a network attack scenario, an attacker could place a legitimate Microsoft Lync-related file and a specially crafted DLL in a network share, a UNC, or WebDAV location and then convince the user to open the file.

What systems are primarily at risk from the vulnerability? 
Systems where Microsoft Lync is used, including workstations and terminal servers, are primarily at risk. Servers could be at more risk if administrators allow users to log on to servers and to run programs. However, best practices strongly discourage allowing this.

What does the update do? 
The update addresses this vulnerability by correcting how Microsoft Lync loads external libraries.

Is this vulnerability related to Microsoft Security Advisory 2269637?
Yes, this vulnerability is related to the class of vulnerabilities, described in Microsoft Security Advisory 2269637, that affects how applications load external libraries.

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

Microsoft has not identified any mitigating factors for this vulnerability.

Microsoft has not identified any workarounds for this vulnerability.

What is the scope of the vulnerability? 
This is an information disclosure vulnerability. An attacker who successfully exploited the vulnerability could perform cross-site scripting attacks against Lync or Microsoft Communicator users. An attacker could then potentially run script on behalf of a victim user.

What causes the vulnerability? 
The vulnerability is caused by the way that SafeHTML sanitizes HTML.

Is this vulnerability related to CVE-2012-1858 in MS12-037, Cumulative Security Update for Internet Explorer? 
Yes, the HTML Sanitization Vulnerability, CVE-2012-1858, also affects Internet Explorer.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited the vulnerability could perform cross-site scripting attacks against Lync or Microsoft Communicator users. An attacker could then potentially run script on behalf of a victim user.

How could an attacker exploit the vulnerability? 
To exploit this vulnerability, an attacker must have the ability to submit a specially crafted script to a Lync or Microsoft Communicator chat window. Because of the vulnerability, in specific situations the specially crafted script is not properly sanitized, which subsequently could lead to an attacker-supplied script being run in the security context of a user who views the malicious content.

For cross-site scripting attacks, this vulnerability requires that a user receives a specially crafted chat message for any malicious action to occur.

What systems are primarily at risk from the vulnerability? 
Systems where Lync or Microsoft Communicator are used frequently, such as workstations or terminal servers, are at the most risk from this vulnerability.

What does the update do? 
The update addresses the vulnerability by modifying the way that SafeHTML sanitizes HTML content.

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

Reference Table

The following table contains the security update information for this software. You can find additional information in the subsection, Deployment Information, in this section.