Microsoft Security Bulletin MS12-002 - 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:

• For an attack to be successful, a user must visit an untrusted remote file system location or WebDAV share and open a legitimate file.
• 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 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.

• Register packager.exe with a full path

  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 Registry Editor at your own risk.

  We recommend that you back up the registry before you edit it.

  To register package.exe with a full path, perform the following steps:

  1. Click Start, click Run, type regedit, and then click OK.
  2. Expand HKEY_CLASSES_ROOT, then Package, then Protocol, then StdFileEditing, then Server.
  3. Click on the (Default) key and change the value to:

     C:\Windows\System32\Packager.exe

     Note Substitute the appropriate system path for your system.

What is the scope of the vulnerability? 
This is a remote code execution vulnerability. An attacker who successfully exploited this vulnerability 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.

What causes the vulnerability? 
The vulnerability is the result of an improper registration and implementation of the Windows Object Packager in affected releases of Microsoft Windows.

What is Windows Object Packager? 
Windows Object Packager is a tool that can be used to create a package that can be inserted into a file. For more information about Object Packager, see the following Microsoft Product Documentation.

What might an attacker use the vulnerability to do? 
An attacker who successfully exploited this vulnerability could run arbitrary code as the logged-on user. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. If a user is logged on with administrative user rights, an attacker could take complete control of the affected system. 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? 
In a network attack scenario, an attacker could place a legitimate file with an embedded packaged object and a specially crafted executable file in a network share, a UNC, or WebDAV location and then convince the user to open the legitimate file.

What systems are primarily at risk from the vulnerability? 
Workstations, where users may be expected to open files from untrusted network locations, are primarily at risk. Servers could also be at 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 a registry key associated with the Windows Object Packager.

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.

Note The update for supported versions of Windows XP Professional x64 Edition also applies to supported versions of Windows Server 2003 x64 Edition.

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.

Note The update for supported versions of Windows Server 2003 x64 Edition also applies to supported versions of Windows XP Professional x64 Edition.