An autorun.inf file is a text file that can be used by the AutoRun and AutoPlay components of Microsoft Windowsoperating systems. For the file to be discovered and used by these component, it must be located in the root directory of a volume. As Windows has a case-insensitive view of filenames, the autorun.inf file can be stored as AutoRun.inf or Autorun.INF or any other case combination. The AutoRun component was introduced in Windows 95 as a way of reducing support costs. AutoRun enabled application CD-ROMs to automatically launch a program which could then guide the user through the installation process. By placing settings in an autorun.inf file, manufacturers could decide what actions were taken when their CD-ROM was inserted. The simplest autorun.inf files have just two settings: one specifying an icon to represent the CD in Windows Explorer and one specifying which application to run. Extra settings have been added in successive versions of Windows to support AutoPlay and other new features.
The autorun.inf file
autorun.inf is an ASCII text file located in the root folder of a CD-ROM or other volume device medium. The structure is that of a classic Windows.ini file, containing information and commands as "key=value" pairs, grouped into sections. These keys specify:
The name and the location of a program to call when the medium is inserted.
The name of a file that contains an icon that represents the medium in Explorer.
Commands for the menu that appears when the user right-clicks the drive icon.
The default command that runs when the user double-clicks the drive icon.
Settings that alter AutoPlay detection routines or search parameters.
Settings that indicate the presence of drivers.
Abuse
Autorun.inf has been used to execute a malicious program automatically, without the user knowing. This functionality was removed in Windows 7 and a patch for Windows XP and Vista was released on August 25, 2009 and included in Microsoft Automatic Updates on February 8, 2011.
Inf handling
The mere existence of an autorun.inf file on a medium does not mean that Windows will automatically read it or use its settings. How an inf file is handled depends on the version of Windows in use, the volumedrive type and certain Registry settings. Assuming Registry settings allow, the following autorun.inf handling takes place:
This simple autorun.inf file specifies setup.exe as the application to run when AutoRun is activated. The first icon stored within setup.exe itself will represent the drive in Explorer: open=setup.exe icon=setup.exe,0 label=My install CD
Sections
Following are the sections and keys allowed in a valid autorun.inf. There also exist architecture specific section types for systems such as Windows NT 4 running on RISC. However these are long outdated and not described here.
The autorun section contains the default AutoRun commands. An autorun.inf file must contain this section to be valid. Keys allowed are: ; action=text ; action=@filename,-resourceID ; icon=iconfilename ; label=text ; open=exefile filename exefileparam1 [param2... ; shell\verb=menu text ; shell=verb
shell\readme\command=notepad readme.txt shell\readme=Read & Me shell=readme
The Content section allows authors to communicate the type and intent of content to AutoPlay without AutoPlay having to examine [the media. Valid keys are: MusicFiles, PictureFiles, VideoFiles. Each key can be set to indicate true or false values and values are not case sensitive. ; true or ; false or Example: MusicFiles=Y PictureFiles=0 VideoFiles=false
Limits AutoPlay's content search to only those folders listed, and their subfolders. The folder names are always taken as absolute paths whether or not a leading slash is used. Example: \pictures \music more music\special
AutoPlay's content search system will not scan the folders listed, nor their subfolders. IgnoreContentPaths takes precedence over ExclusiveContentPaths so if a path given in a [IgnoreContentPaths] section is a subfolder of a path given in an [ExclusiveContentPaths] section it is still ignored. Example: pictures \music more music\special
This section is used to indicate where driver files may be located. This prevents a lengthy search through the entire contents of a CD-ROM. Windows XP will fully search:
without this section present. All other media should include this section to have Windows XP autodetect any drivers stored on that media. The section is not used with AutoRun or AutoPlay and is only referred to during a driver installation phase. The only valid key is: DriverPath=directorypath which lists a path Windows will search for driver files. All subdirectories of that path are also searched. Multiple key entries are allowed. If no DriverPath entry is provided in the section or the DriverPath entry has no value, then that drive is skipped during a search for driver files. Example: DriverPath=drivers\video DriverPath=drivers\audio open=setup.exe icon=setup.exe,0 label=My install CD
