AutoRun

AutoRunand the companion featureAutoPlayare components of theMicrosoft Windowsoperating systemthat dictate what actions the system takes when a drive ismounted.

AutoRun was introduced inWindows 95to ease application installation for non-technical users and reduce the cost of software support calls. When an appropriately configuredCD-ROMis inserted into a CD-ROM drive, Windows detects the arrival and checks the contents for a special file containing a set of instructions. For a CD containing software, these instructions normally initiate installation of the software from the CD-ROM onto the hard drive. To maximise the likelihood of installation success, AutoRun also acts when the drive is accessed ( "double-clicked") inWindows Explorer(or "My Computer" ).

Until the introduction ofWindows XP,the terms AutoRun and AutoPlay were used interchangeably, developers often using the former term and end users the latter. This tendency is reflected in Windows Policy settings named AutoPlay that change Windows Registry entries named AutoRun, and in theautorun.inffile which causes "AutoPlay" to be added to drives’context menus.The terminology was of little importance until the arrival of Windows XP and its addition of a new feature to assist users in selecting appropriate actions when new media and devices were detected. This new feature was calledAutoPlayand a differentiation between the two terms was created.

AutoRun, a feature of Windows Explorer (actually of the shell32dll) introduced in Windows 95, enables media and devices to launch programs by use of command listed in a file calledautorun.inf,stored in theroot directoryof the medium.

Primarily used on installation CD-ROMs, the applications called are usually application installers. The autorun.inf file can also specify an icon which will represent the device visually in Explorer along with other advanced features.

The terms AutoRun and AutoPlay tend to be interchangeably used when referring to the initiating action, the action that detects and starts reading from discoveredvolumes.AutoRun is positioned as a layer between AutoPlay and the Shell Hardware Detection service which may help in understanding the terminology. However, to avoid confusion, this article uses the term AutoRun when referring to the initiating action.

AutoPlay

AutoPlay inWindows 8and later

AutoPlay inWindows Vista

AutoPlayis a feature introduced in Windows XP which examines removable media and devices and, based on content such as pictures, music or video files, launches an appropriate application to play or display the content.If available, settings in an autorun.inf file can add to the options presented to the user.

AutoPlay is based on a set of handler applications registered with the AutoPlay system. Each media type (Pictures, Music, Video) can have a set of registered handlers which can deal with playing or display that type of media.

Each hardware device can have a default action occurring on discovery of a particular media type, or the AutoPlay dialog can prompt the user what action to take.

AutoRun activation

The AutoRun sequence starts with the initial discovery of a new device or new piece of media. Following this, notification of interested parties occurs, of which the Windows Explorer shell is of primary interest. After checking certainRegistrysettings to see if AutoRun can proceed, parsing of an optional autorun.inf may occur and any necessary actions are taken.

The initial sequence is handled much the same in every version of Windows from Windows 95. However, the way the autorun.inf file is read and acted upon and the level of integration of AutoRun with AutoPlay has changed significantly from the time AutoPlay was introduced in Windows XP until the present handling inWindows 7.InWindows 10,Microsoft has added the option to enable autorun in its settings. Not only users can turn it on but also they can choose specific external devices for autoplay.

Initiation and notification

When a device with AutoRun-compatible drivers receives new media, a "Media Change Notification" event occurs. The WindowsOSthen notifies interested applications that a device change has occurred. The notification method used can change depending on the device type.

If the device changed is a volume (like a CD) or a port (like a serial port) Windows broadcasts aWM_DEVICECHANGEnotification to all top-level windows.Windows calls this a "basic" notification. A top-level window is one which is a descendant of the desktop.

However, if the device changed is not one of these types an application can use theRegisterDeviceNotificationfunction to register to receive device notifications.

An article on the CodeProject website,"Detecting Hardware Insertion and/or Removal",withclarificationsfrom ablogby Doran Holan is of particular technical interest here.

Non-volume devices are those devices that do not appear as drive letters in "My Computer". These are not handled by any part of AutoRun - any actions taken for these devices are taken either by device specific software or by AutoPlay. SeeAutoPlay#Devices that are not drives.

When Explorer receives notification of avolumechange, it performs a number of actions:

1. Checks to see if AutoRun has been disabled through the Registry. If AutoRun is disabled for that drive or drive type, Explorer does not proceed further. There have beenbugsin this area.
2. Checks that the root directory of the inserted media contains an autorun.inf file, which might be read. Seebelow.
3. Sends aQueryCancelAutoPlaymessage to the foreground window. An application which has registered its interest in receiving this message usingRegisterWindowMessagecan respond to this message to halt AutoRun (and thus AutoPlay) at this point. Any application, foreground or not, can also be notified by using theIQueryCancelAutoPlayCOMinterfaceavailable in Windows XP and later.
4. Altersdouble-clickand contextual menu behaviours. When a user double clicks on the drive icon in Explorer or right clicks to get a context menu, what happens is fully programmable by settings in the autorun.inf file.
5. Adds an autorun.inf controllable icon and descriptive text to the drive icon.
6. Checks to see if the⇧Shiftkey is held down. If it is then Windows Vista (and later Windows versions) will invoke the AutoPlay dialog regardless of settings to the contrary.Previous versions of Windows will not continue with the process.
7. Finally, if this point has been reached, either:
   • takes no further action.
   • executes the "AutoRun task", the application optionally specified in theopenorshellexecutekeys in an autorun.inf's[autorun]section.
   • invokes AutoPlay.

   Which choice is made depends on the version of Windows in use, instructions from the autorun.inf if available and the type of the media discovered.

Changing behaviour

See also:autorun.inf § Inf handling

Before AutoPlay

On Windows versions prior to Windows XP, an autorun.inf file on any drive type will be read and its instructions followed. The AutoRun task, if specified, is executed immediately without user interaction.This includes DRIVE_REMOVABLE, DRIVE_FIXED and DRIVE_REMOTEdrive types.

AutoRun will work with network drives (the DRIVE_REMOTE drive type) that are mapped to a drive letter. AutoRun will also work with floppy drives that are provided with autorun-compatible drivers.

The default Registry settings on Windows versions prior to Windows XP (SeeNoDriveTypeAutoRun), disable Remote and Removable drives from AutoRun initiation, leaving Fixed and CDROM drive types active by default.

Introducing AutoPlay

With the introduction of AutoPlay in Windows XP, the final stage action (stage 7 above) for some drive types changed from executing an application to invoking AutoPlay. From Windows Vista, the AutoPlay system is integrated into every aspect of media handling and there is no automatic execution of the AutoRun task.

The default Registry settings add Removable drives to those that initiated AutoRun. In Windows XP and higher,exceptWindows Server 2003, only the Unknown and Remote drive types are not active for AutoRun.

The handling of the autorun.inf file changes very significantly between each Windows version. The details can be found in theautorun.infarticle. The current handling in Windows 7 is thatonlydrives of type DRIVE_CDROM may specify an AutoRun task, alter double-click behaviour or change context menus.

Registry settings

AutoRun consultsWindows Registryvalues to decide whether to initiate actions for any particular drive or drive type. These values can be changed using several methods, one of which is usingGroup Policy.

The primary relevant Registry entry names areNoDriveTypeAutoRunandNoDriveAutoRun.These exist in both per-machine and per-user settings and their location and priority in the Registry are described in further detail below.

Drive types

The drive types are distinguished by Type Name as follows:

Type name	value	Description
DRIVE_UNKNOWN	0x00000000	The drive-type could not be determined (generic drive)
DRIVE_NO_ROOT_DIR	0x00000001	The drive is currently invalid (no mounted volumes)
DRIVE_REMOVABLE	0x00000002	The drive has removable media (floppy drive,USB flash drive)
DRIVE_FIXED	0x00000003	The disk cannot be removed from the drive (hard disk/solid state drive)
DRIVE_REMOTE	0x00000004	The drive is a remote (network) drive
DRIVE_CDROM	0x00000005	The drive is a CD-ROM, DVD-ROM or BD-ROM drive
DRIVE_RAMDISK	0x00000006	The drive is aRAM disk
DRIVE_NOT_DETERMINED	0x00000007	The drive has not yet been determined
DRIVE_NOT_FOUND	0x00000008	The drive currently can't be accessed (detached drives)
[RESERVED]	0x00000009	This value reserved for future-technologies

Registry terminology

The Windows Registry is a hierarchicaldatabasethat stores configuration settings and options for the operating system. The terminology is somewhat misleading so it is briefly summarised here.

A Registrykeyis similar to a folder that, in addition to values, each key can contain subkeys which in turn may contain subkeys, and so on.

A Registryvalueconsists of a name-data pair. Microsoft documentation commonly uses the term "entry" as an equivalent term. It also uses "value" for "data" when it is obvious what is meant. To avoid confusion, this article always uses the term "entry" when referring to the name-data pair.

Two Registry keys that are very commonly referred to areHKEY_LOCAL_MACHINEwhich contains per-machine settings, andHKEY_CURRENT_USERwhich contains settings for the currently logged-on user. These are almost always abbreviated asHKLMandHKCUrespectively. There may be many users of a machine; their settings are stored inHKEY_USERS,HKCUis actually just a link to the appropriate place inHKEY_USERS.

Changing Registry settings

Registry settings may be changed directly by using the GUIregedittool or the command linereg.exeutility. Settings can also be placed in atext file,named with a.reg extension type. For example, "mychanges.reg".When the file is double clicked, the settings in the file are entered into the Registry, permissions allowing.

They can be changed indirectly by using Group Policy, applied locally to a single computer withGPEdit.mscor to a domain withgpmc.msc.

It may be necessary to either logout or restart the computer in order for any Registry changes to take effect.

Evaluation order

TheNoDriveAutoRunandNoDriveTypeAutoRunRegistry entries can exist in two places, the per-user setting (under HKEY_CURRENT_USER) and the per-machine setting (under HKEY_LOCAL_MACHINE). If an entry appears under HKEY_LOCAL_MACHINE, then any corresponding entry under HKEY_CURRENT_USER is completely ignored. The data values are not merged in any way.

When deciding whether to activate AutoRun, bothNoDriveAutoRunandNoDriveTypeAutoRunRegistry entries are consulted. If either value indicates a drive should be disabled then AutoRun is disabled for that drive.

Thus in the following example:

HKEY_LOCAL_MACHINE		HKEY_CURRENT_USER
NoDriveAutoRun	NoDriveTypeAutoRun	NoDriveAutoRun	NoDriveTypeAutoRun
0x08	(Not Present)	0x03FFFFFF	0x95

the data value taken forNoDriveAutoRunis 0x08, disabling drive D and the data value taken forNoDriveTypeAutoRunis 0x95, disabling removable and network drives. The per-userNoDriveAutoRunentry is never used.

NoDriveTypeAutoRun

HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Entry name	Data type	Range	Default
NoDriveTypeAutoRun	REG_DWORD	0x00 to 0xFF	0x95 or 0x91

This Registry entry disables or enables the AutoRun feature on all drives of the type specified.It reflects the setting of the relevant Autoplay Group Policy. Valid data ranges from 0x00 to 0xFF inhexadecimalnotation. If the entry is not present, the default data value is either 0x95 or 0x91 depending on the version of Windows used. An entry present in HKLM overrides any entry present in HKCU.

The entry data is a bitmapped value, where a bit set to 1 disables AutoRun on a particular type of drive. The bit settings for each type of drive are shown below:

drive type bitwise settings

Note that bit number 1 is unused and that the "Unknown" type is represented twice. Setting all bits to 1 would give a hexadecimal value of 0xFF, decimal 255, and would disable AutoRun on all types of drives.

The default setting for this entry depends on the version of Windows being used:

Operating system	Default setting
Windows 7	0x91
Windows Server 2008	0x91
Windows Vista	0x91
Windows Server 2003	0x95
Windows XP	0x91
Windows 2000	0x95
Windows 95/98	0x95

NoDriveAutoRun

HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Entry name	Data type	Range	Default
NoDriveAutoRun	REG_DWORD	0x0 to 0x03FFFFFF	0x0

This Registry entry disables or enables the AutoRun feature on individual drives.It is not associated with a Group Policy and does not exist by default. The data value is taken to be 0 if the entry is not present. An entry present in HKLM overrides any entry present in HKCU.

The data is a 32 bit (DWORD) bitmapped value, of which the lower 26 bits are used to represent each of the 26 drive letters from A to Z. Thus the valid data range is from 0x0 to 0x03FFFFFF. The least significant bit (the right most bit) represents drive A, and the 26th bit from the right represents drive Z.

A bit set to 1 disables AutoRun on a particular drive. For example, if the data value is set to 0x8 (1000 binary), AutoRun is disabled on drive D.

Group Policy

TheGroup Policysettings dialog box onWindows XPshowing option to turn off AutoPlay.

The only Group Policy settings available for AutoRun affect theNoDriveTypeAutoRunRegistry entries. The policy is available on either a per-machine or a per-user basis reflecting the Registry entry location in either HKLM or HKCU.As describedabove,a per-machine policy setting will cause the per-user policy setting to be ignored.

When a policy isEnabled,Group Policy will add theNoDriveTypeAutoRunentry to the Registry. If the policy isDisabledor set toNot configured,Group Policy deletes this entry from the Registry for the Machine policy (in HKLM) and sets it back to system defaults value for the User policy (in HKCU). System defaults may then take effect as described in theNoDriveTypeAutoRunsection.

The policy names, locations and possible settings vary slightly between Windows versions. The list of settings are relatively short and are always additional to the system default setting. Therefore, on Windows 2000, enabling the "Disable Autoplay" policy and setting it to "CD-ROM drives", disables AutoRun (as distinct from AutoPlay) for CD-ROM and DVD drives, removable drives, network drives, and drives of unknown type.

This setting cannot be used to enable AutoRun on drives on which it is disabled by default or disable AutoRun for drives not listed. To disable or enable any particular drives or drive types, the Registry must be edited manually.

Windows Server 2003, Windows XP, and Windows 2000

The per-machine policy location is:

Group Policy \ Computer Configuration \ Administrative Templates \ System

The per-user policy location is:

Group Policy \ User Configuration \ Administrative Templates \ System

The relevant policy is "Turn off Autoplay". In Windows 2000 the policy is called "Disable Autoplay" instead.

Once the policy is Enabled it can be set to "All drives" or "CD-ROM drives". The latter setting adds CD-ROM drives to the existing list of disabled drive types as described above.

Windows Vista, Windows Server 2008

The per-machine policy location is:

Computer Configuration \ Administrative Templates \ Windows Components \ Autoplay Policies

The per-user policy location is:

User Configuration \ Administrative Templates \ Windows Components \ AutoPlay Policies

The relevant policy is "Turn off Autoplay" and can be set for CD-ROM, DVD-ROM and removable drives or all drives.

Two related policies were added in Vista and Server 2008:

Default behavior for AutoRun

HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Entry name	Data type	Range	Default
NoAutoRun	REG_DWORD

Sets the default behavior for AutoRun commands found in autorun.inf files.

Prior to Windows Vista, when media containing an autorun.inf specifying an AutoRun task was:inserted, the default action was to automatically execute the program without user intervention.:From Windows Vista the default behaviour is to invoke AutoPlay and represent the AutoRun task as:one of the dialog options. This is also the behaviour when this policy is Not configured or:Disabled.

If this policy is Enabled, the behaviour can be changed to either:

• Completely disable autorun.inf commandsor
• Automatically execute the autorun.inf command as per previous Windows versions.

Don't set the always do this checkbox

HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
Entry name	Data type	Range	Default
DontSetAutoplayCheckbox	REG_DWORD

If this policy is Enabled, the "Always do this..." checkbox in the AutoPlay dialog will not be set:by default when the dialog is shown.

Windows 7, Windows Server 2008 R2

In these versions of Windows, the ability of an autorun.inf file to set an AutoRun task, alter double-click behaviour or change context menus is restricted to drives of type DRIVE_CDROM. There are no policy settings that will override this behaviour. Policy locations and settings are as perWindows Vista, Windows Server 2008above with the addition of:

Turn off Autoplay for non-volume devices

HKLM\Software\Policies\Microsoft\Windows\Explorer HKCU\Software\Policies\Microsoft\Windows\Explorer
Entry name	Data type	Range	Default
NoAutoplayfornonVolume

If this policy is enabled, AutoPlay will be disabled fornon-volumedevices.

Altering AutoRun behaviour

Pressing the Shift key

If the⇧ Shiftkey is held down at a certain point in the execution sequence, Windows Vista invokes the AutoPlay dialog regardless of any AutoPlay settings to the contrary.Previous versions of Windows do not execute the AutoRun task. It is essential that theleftShift key is used for this purpose as holding down the right Shift key for eight seconds invokes FilterKeys.

Given that Shift must be held down until Windows checks for it, it may be a considerable amount of time before it becomes effective. The time taken primarily depends on the time to recognise the new hardware and the time taken for CD-ROMs to spin up. It is unsafe to rely on this method.

Auto Insert Notification

CertainMedia Change Notificationevents may be suppressed by altering certain Registry entries. "Media Change Notification" is the generic term; for CD-ROM drives, the specific term is "Auto Insert Notification".

HKLM\SYSTEM\CurrentControlSet\Services\Cdrom
Entry name	Data type	Range	Default
AutoRun	REG_DWORD	0 or 1	1

For CD-ROM drives, changing the value of this Registry entry to 0 will disable Auto Insert Notification for CD-ROM drives only.A Windows restart will be necessary.

Data value	Meaning
0	Does not send an MCN message
1	Sends an MCN message

Under Windows 95/98/ME, this setting can be changed under Device Manager, accessible from the System icon in Control Panel.

AutoRun settings forCD-ROMdrive onWindows 98.

Although the Registry entry is named "AutoRun", it only suppresses the MCN message. The MCN message does trigger AutoRun initiation but it also instructs the Explorer shell to update its views and contents.

Thus, as a side effect only, this disables AutoRun for CD-ROM drives. However, Explorer will now not update its view when a new CD is inserted; it will show the contents of the previous CD untilF5is pressed or View/Refresh is selected from the Explorer menu. This could result in severe confusion for users.

For this reason the Media Change Notification message should not be disabled unless there is absolutely no alternative; AutoRun can be disabled for individual drives using Group Policy or the Registry.

HKLM\SYSTEM\CurrentControlSet\Services\Cdrom
Entry name	Data type
AutoRunAlwaysDisable	REG_MULTI_SZ

This entry is used to suppress the MCN message for specifically listed type of CD-ROM drive,primarily CD-ROM changers. The data is a set of device identifiers, which matches those identifiers reported to the system by the devices themselves.

The default value for this entry consists of products identified by Microsoft testing as being unable to support AutoRun. This entry should not be altered from its default.

Editing Group Policy

AutoRun may be suppressed on particular drives and drive types by using the methods described in theGroup Policysection. However, the Group Policy Editor is not available on Home versions of Windows XPand does not provide any fine-grained drive selection facilities.

However, Group Policy would be the accepted method of disabling AutoRun on an entire Windows domain.

Registry files

A Registry setting file can be created that, when executed, makes the desired changes in the Registry.

Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\policies\Explorer] "NoDriveTypeAutoRun"=dword:000000ff Note that the actual file should always end with a blank line. This is not optional.

In the above example, AutoRun would be disabled for all drives and for all users. This example would need to be run as Administrator and a reboot would be needed for the setting to take complete effect.

Initialization file mapping

Windows Vista and later versions of Windows have a policy setting, "Default behavior for AutoRun", that can be set to disallow the reading of an autorun.inf file on any volume. This avoids certain scenarios wheremalwareleverages autorun.inf functionality to infect a machine. Previous versions of Windows do not have this policy setting but the use ofinitialisation file mappingis an effective workaround.

As an autorun.inf file is a standard WindowsINI file,the appropriateAPIcalls are used by Windows when fetching its settings. These API calls can be redirected using the INI file mapping method. The followingRegistry fileillustrates the workaround, where all autorun.inf settings are taken solely from theHKEY_LOCAL_MACHINE\Software\DoesNotExistRegistry key:

Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\IniFileMapping\Autorun.inf] @="@SYS:DoesNotExist"

As this key does not exist, it is as if the autorun.inf file contains no settings information. It is important to note that this applies to any autorun.inf in any location and on any drive.

Since either the policy setting or this workaround disable autorun, installation of software from an autorunning install CD or DVD will obviously no longer be automatic. It will be necessary to view the CD's autorun.inf file and then execute the appropriate install program manually.

Issues and security

Microsoft recognized that "Because code may be executed without user's knowledge or consent, users may want to disable this feature because of security concerns." and released a "Fixit" to disable AutoRun for users not comfortable with editing the registry.

The AutoRun disable bug

From Windows 2000 through to Windows Server 2008, AutoRun-relevant Registry entries were not handled properly leading to a security vulnerability.Windows 95 and Windows 98 were not affected.

When AutoRun is disabled, Windows should not proceed further through theactivationsequence than the Registry check. However, it parses any autorun.inf found and does everything except the final action to invoke AutoPlay or execute an application.

This leaves the user open to attack from malware which uses the autorun.inf to alter the double-click and contextual menu behaviours. Double clicking the drive icon will infect the machine. Right Clicking and selecting the "Explore" or "Open" options from the context menu is not a workaround as these menu items can be coopted by the appropriate autorun.inf entries.

This bug was fixed in a number of security updates, detailed inMicrosoft Knowledge Basearticle 967715.

Other issues

• If one adds the computer to an Active Directory domain, theNoDriveTypeAutoRunvalue may be reset to a default value.This is due to Group Policy settings in the domain taking effect. This is not a bug.
• Some programs may deliberately change AutoRun Registry settings. Early versions of CD burning software like Roxio have been known to change settings in this way.
• If the Group Policy "Restrict CD-ROM access to locally logged-on user only" security option under:

  Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

  is turned on (Enabled), then AutoRun may not function.

  Windows Installers will also malfunction because "Local System" access to the CD-ROM will be denied.

  This Group Policy setting reflects the value of the Registry entry:

  HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
  Entry name	Data type	Range	Default
  allocatecdroms	REG_SZ	0 or 1	0

  and should be set to 0.
• RealPlayer 10 interferes with AutoPlay functionality to the extent that it may look as if AutoRun or AutoPlay is not working at all.

Attack vectors

AutoRun functionality has been used as a malware vector for some time. Prior to Windows Vista, the default action with a CD-ROM drive type was to follow any autorun.inf file instructions without prompts or warnings. This makes rogue CD-ROMs one possible infection vector.

In the same category are mixed content CD-ROMs. An audio CD, that a user would not expect to contain software at all, can contain a data section with an autorun.inf. Some companies, such asSony BMG,have used this vector to install malware that attempts to protect against copying of the audio tracks.

U3enabled flash drives, byemulatinga CD-ROM unit, can also cause Windows to execute commands from the autorun.inf found on the emulated CD-ROM.

Devices like theHuawei E220HSDPA modem validly use this method to autoinstall drivers for the modem itself. However, plugging in a flash drive from an unknown source is an unwise move.USB Switchbladeand similar tools have made U3 flash drive attacks trivial. Given the ease of writingscriptbased attacks,anti-virussoftware may be ineffective in preventing data and password stealing.

TheConfickerwormin actionscreenshot onWindows 7.

With a standard flash drive, social engineering attacks can be employed to entice a user to click on the appropriate item in the AutoPlay dialog. An alluringactionstring promising free games or pornography would lure many users into the trap. At any time, double clicking on the drive icon will use the autorun.inf automatically, a trap more advanced users could fall into.

Any user can configure AutoPlay to make various decisions for them; by checking the appropriate box in the AutoPlay dialog, running flash drive malware becomes silent and automatic.

AutoRun malware has been extended to use hard drives,picture frames and other digital devices.Care in dealing with external devices is a security priority. The prevalence of malware infection by means of AutoRun and USB flash drive was documented in a 2011 Microsoft studyanalyzing data from more than 600 million systems worldwide in the first half of 2011. The study found that 26 percent of all malware infections of Windows system were due to USB flash drives exploiting the AutoRun feature inMicrosoft Windows.That finding was in line with other statistics, such as the monthly reporting of most commonly detected malware by antivirus company ESET, which lists abuse of autorun.inf as first among the top ten threats in 2011.

Attack mitigation

In addition to basic security precautions, which include

• following theprinciple of least privilegeby not habitually running withAdministratorprivileges and
• applying all relevant security patches and updates,

exposure to these attacks can be minimised through the appropriate use of Group Policy and Registry settings. The following security policies are a summary of those described within this article:

• Disable AutoRun (but see theAutoRun disable bug)
• Use the "Default behavior for AutoRun" Group Policy under Vista (seeabove) to disable autorun.inf commands
• Useinitialization file mappingto nullify autorun.inf sections
• Under Windows 7, only CD and DVD drives may specify applications like the AutoRun task in the autorun.inf file. Windows XP and later can bepatchedto behave in the same way with updateKB971029.In February 2011, this patch was added to the officialWindows Updatechannel.The Windows 7 AutoRun task behaviour now becomes the default for all current versions of the Windows OS.

In addition, the following actions have been recommended by Microsoft, primarily during theConfickerworm attacks:

• Prevent autorun.inf invocation from network shares by:
  1. Deleting any existing autorun.inf file from the root of a mapped network drive
  2. Denying Create rights to the root of a mapped network drive
• Prevent the use of USB storage devices by means of:
  • USB settings within theSystem BIOS
  • Appropriate Registry settings as described in Knowledge Base article823732
  • Setting USB devices to read only to prevent propagation of unknown worms (and theft of proprietary data)

See also

• AutoPlay
• autorun.inf

External links

• AutoRun and AutoPlay Reference,Microsoft,MSDN Library
• Memory stick worms,Nick Brown's blog
• Autorun Protector,A standalone software that prevents PC from autorun worms and protects the removable device from being infected from other sources.
• Dan McCloy's Autorun Reference Guide
• Security Watch Island Hopping: The Infectious Allure of Vendor Swag,TechNet Magazine
• Figure 4: querycancelautoplay example code,Microsoft Systems Journal,September 1998
• AutoPlay Repair Wizard,Microsoft Download Center
• Test your defenses against malicious USB flash drives,Computerworld blog, January 24, 2009
• The best way to disable Autorun for protection from infected USB flash drives,Computerworld blog, January 30, 2009
• How To Remove AutoRun Virus
• Microsoft PowerToys,Microsoft,Tweak UI
• Online Information Resourceon the autorun/autostart feature of Microsoft Windows
• AutoRunConfsimple configuration tool for Autorun settings.
• How to Enable / Disable Autorun for a Drive (using Registry)
• Disable Autorunturn on/off the autorun/autoplay feature of Windows
• Create an AutoRun MenuCreate your own AutoRun Menu