Type name: image

Subtype name: emf

Required parameters: None.

Optional parameters: None.

Encoding considerations: Binary.

Security considerations:

   Enhanced Metafiles are not afflicted with the Metafile Image Code
   Execution ("MICE") vulnerability.  There has been no public
   disclosure of vulnerabilities specific to EMF or EMF+ to date.
   Neither EMF nor EMF+ are designed to contain "active content".
   Nonetheless, Enhanced Metafiles can contain Encapsulated
   PostScript (EPS) data; thus, the security considerations of
   PostScript processing may also apply to EMF.

   As the original intent was to replicate Windows GDI calls, flaws
   in GDI, or in a display or printer driver implementing the backend
   to GDI, could be exploitable with maliciously crafted EMF content.
   EMF implementations not backed by Windows GDI have different
   risks: namely, while a malicious EMF author may not consider the
   non-Windows GDI implementation as a primary target, EMF has many
   "corner case" records for which an implementation's processing may
   not have received the same level of scrutiny as the Windows
   implementation.  "Fuzzing" the implementation is appropriate.  It
   is also possible that EMF+ data is "safe" while EMF data contains
   an exploit (or vice versa); the EMF+-aware implementation (such as
   an application designed for GDI+ on Windows XP or above) would
   skip the "unsafe" data while another implementation would fall
   prey to the exploit.

   As a "basic" image format, the image/emf media type does not
   employ executable content and provides no facilities for privacy
   or integrity.

Interoperability considerations:

   Enhanced Metafile is the 32-bit metafile format; it was released
   in 1992 along with Windows NT 3.1.  There is a large body of free
   and commercially available clip art that is still in use, either
   independently or embedded in productivity documents (word
   processing documents, desktop publishing documents, slideshows,
   presentations, spreadsheets, and workbooks).  To say that support
   for this format is necessary for interoperability would not be an
   understatement.

   Enhanced Metafiles have extensive accommodations for comments and
   arbitrary data storage.  Enhanced Metafiles can store and output
   text strings.  Mercifully, the encodings of these strings are
   well-defined.  Record examples include EMR_EXTTEXTOUTA (US-ASCII),
   EMR_EXTTEXTOUTW (UTF16-LE), EMR_POLYTEXTOUTA (US-ASCII),
   EMR_POLYTEXTOUTW (UTF16-LE), and EMR_SMALLTEXTOUT (UTF16-LE or the
   low-order 8 bits of UTF16-LE -- effectively ISO-8859-1 --
   depending on ETO_SMALL_CHARS).

   Enhanced Metafiles can contain Encapsulated PostScript (EPS) data
   in the EpsData object.  The FormatSignature EPS_SIGNATURE
   (0x46535045, in little-endian) is used instead of
   ENHMETA_SIGNAUTRE (0x464D4520, in little-endian) in such a case.

   Windows XP introduced the GDI+ API, along with EMF+.  EMF+ is
   actually an embedded format in which GDI+ commands are stored as
   EMF comment records (EMR_COMMENT_EMFPLUS record type).  Content
   containing EMF+ data can be identified as "EMF+ Only" (only EMF+;
   the EMF records are not sufficient to reconstitute the drawing) or
   "EMF+ Dual" (both EMF records alone or EMF+ records alone, when
   played back, are sufficient to reconstitute the drawing).  Support
   for EMF+ records may not be as extensive as support for the
   original EMF records.

   The previously unregistered type image/x-emf is also in wide use.
   Accordingly, it is registered as a deprecated alias.

Published specification:

   EMF: Microsoft Corporation, "[MS-EMF]: Enhanced Metafile Format",
   v20160714 (Rev 12.0), July 2016,
   <http://msdn.microsoft.com/library/cc230514>.

   EMF+: Microsoft Corporation, "[MS-EMFPLUS]: Enhanced Metafile
   Format Plus Extensions", v20160714 (Rev 14.1), July 2016,
   <http://msdn.microsoft.com/library/cc230724>.

Applications that use this media type:

   Office productivity applications; clip art applications; desktop
   publishing applications; some web browsers (e.g., Internet
   Explorer).

Fragment identifier considerations: None.

Additional information:

   Deprecated alias names for this type: image/x-emf

   Magic number(s):
      01 00 00 00 (little-endian DWORD 0x00000001), corresponding to
      the EMR_HEADER Type field.
      The next field (EMR_HEADER Size) should be at least 88 (little-
      endian DWORD 0x00000050).

   File extension(s): .emf (for both EMF and EMF+ content)

   Macintosh file type code(s):
      None.  A uniform type identifier (UTI) of "com.microsoft.emf"
      is suggested.

Person & email address to contact for further information:

   Sean Leonard <dev+ietf&seantek.com>

Restrictions on usage: None.

Author/Change controller: Sean Leonard <dev+ietf&seantek.com>

Intended usage: COMMON

Provisional registration? No