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Monday, April 18, 2011


Windows Vista Fails to Handle Malicious AutoRun-enabled CD-ROMS and USB Drives~~~~~~

Windows Vista fails to properly handle the NoDriveTypeAutoRun registry value, which may prevent Vista from effectively disabling AutoRun and AutoPlay features.

I. Description
AutoRun, which was introduced with Windows 95, is a feature that causes Windows to automatically take an action when a removable media device is inserted. For example, when an AutoRun-enabled CD-ROM is inserted, Windows may automatically execute a program on that disc.

This also holds true for U3-enabled USB devices, which emulate a CD-ROM device as well as provide USB mass storage capabilities. These devices can automatically execute code when they are inserted into a Windows system. The AutoRun action can also take place when the user clicks the icon for an AutoRun-enabled device. AutoRun is enabled by default in Windows.

AutoPlay, which was introduced with Windows XP, extends AutoRun capabilities to also allow a menu to be presented to the user, which lists actions that the user may take. AutoRun and AutoPlay can be disabled by setting the CDRom Autorun registry value to 0 and also setting the NoDriveTypeAutoRun registry value to 0xFF. The NoDriveTypeAutoRun registry value is directly tied to the Group Policy setting for "Turn off Autoplay."

Windows Vista fails to properly handle the NoDriveTypeAutoRun registry value. According to Microsoft's documentation, setting NoDriveTypeAutoRun to 0xFF should disable AutoPlay for all types of drives. However, when this registry value is present, Vista enables some AutoPlay features that may not have been enabled prior to setting that registry value.

For example, if NoDriveTypeAutoRun is set to 0xFF, Vista may execute a program specified in the Autorun.inf file when the device icon is clicked. Other values for NoDriveTypeAutoRun may also enable certain AutoPlay features in Vista.

II. Impact
Windows Vista may have some AutoPlay enabled, even though the Group Policy Editor and associated registry values indicate otherwise. This may allow an attacker to cause a user to inadvertently execute arbitrary code on a removable device, such as a USB drive.

III. Solution
We are currently unaware of a practical solution to this problem. Please consider the following workarounds:

Disable AutoRun and AutoPlay in Vista
With limited testing, it appears to be possible to disable AutoRun and AutoPlay on Windows Vista systems by taking the following steps:
  • Set the Autorun registry value for CDs to 0. This will prevent Windows from sending a Media Change Notification (MCN) message when a CD-ROM is inserted, which will in turn prevent AutoPlay with these devices.
  • Disable AutoPlay for all media and devices, by clearing the Use AutoPlay for all media and devices setting in the Windows Control Panel. Details for how to do this are available in the Windows Help and How-to.
  • Do not set the NoDriveTypeAutoRun registry values in HKLM or HKCU. If they are present, we recommend removing the values. This can be also be accomplished by using the Group Policy Editor to set the "Turn off Autoplay" option to "Not Configured"
  • Set the "Default behavior for Autorun" to Enabled - "Do not execute any autorun commands" in the Group Policy Editor.
The relevant settings in the Group Policy editor can be reached by running gpedit.msc and going to Local Computer Policy -> Computer Configuration -> Administrative Templates -> Windows Components -> AutoPlay Policies.

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