Dangerous Flash Drives – part 2

The story continues. Microsoft released their Security Advisory with workarounds regarding the „ .lnk vulnerability “ described in our previous blog post.  To help you protect your systems, here are the two official workarounds, or you can visit the official Microsoft website to find the whole article:

Microsoft Security Advisory (2286198)

http://www.microsoft.com/technet/security/advisory/2286198.mspx

Disable the displaying of icons for shortcuts

Note Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe.

1.	Click Start, click Run, type Regedit in the Open box, and then click OK
2.	Locate and then click the following registry key: HKEY_CLASSES_ROOT\lnkfile\shellex\IconHandler
3.	Click the File menu and select Export
4.	In the Export Registry File dialog box, enter LNK_Icon_Backup.reg and click Save Note This will create a backup of this registry key in the My Documents folder by default

5.	Select the value (Default) on the right hand window in the Registy Editor. Press Enter to edit the value of the key. Remove the value, so that the value is blank, and press Enter.
6.	Restart explorer.exe or restart the computer.

Impact of workaround.Disabling icons from being displayed for shortcuts prevents the issue from being exploited on affected systems. When this workaround is implemented, shortcut files and Internet Explorer shortcuts will no longer have an icon displayed.

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 will still be possible for remote attackers who successfully exploited this vulnerability to cause Microsoft Office Outlook 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.

These were the official Microsoft workarounds.

 

However, there seems to exist also another solution: deploying a GPO that denies running the executable files from all but C drive. This should solve the problem, however, it could be largely uncomfortable (but safe) for users and is recommended only for experienced administrators.

 

Thanks to Peter Gramantik