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Independent Submission                                        S. LeonardRequest for Comments: 7903                                 Penango, Inc.Category: Informational                                   September 2016ISSN: 2070-1721Windows Image Media TypesAbstract   This document registers media types for certain image formats   promulgated in Microsoft Windows, namely image/wmf, image/x-wmf,   image/emf, image/x-emf, and image/bmp for use with Windows Metafile,   Enhanced Metafile, and Windows Bitmap formats.  Originally designed   for Microsoft Windows 2.0 and 3.0, these image files are intended to   be portable between applications and devices, and they may contain   both vector and raster graphics.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   This is a contribution to the RFC Series, independently of any other   RFC stream.  The RFC Editor has chosen to publish this document at   its discretion and makes no statement about its value for   implementation or deployment.  Documents approved for publication by   the RFC Editor are not a candidate for any level of Internet   Standard; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7903.Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.Leonard                       Informational                     [Page 1]

RFC 7903                Windows Image Media Types         September 2016Table of Contents1. Introduction ....................................................21.1. Windows Metafiles ..........................................21.2. Windows Bitmaps ............................................32. Windows Metafile Media Type Registration Application ............43. Enhanced Metafile Media Type Registration Application ...........64. Windows Bitmap Media Type Registration Application ..............95. IANA Considerations ............................................116. Security Considerations ........................................117. References .....................................................117.1. Normative References ......................................117.2. Informative References ....................................11   Author's Address ..................................................121.  Introduction1.1.  Windows Metafiles   Long before the invention of Scalable Vector Graphics, Microsoft   Corporation recognized the value of recording images in a format that   its applications and operating systems could easily render   irrespective of the output device.  With the release of Windows 3.0,   Microsoft released its Windows Metafile (WMF) format, which can   contain vector and raster graphics in one package.  As a binary   format that needed to work on 16-bit machines, WMF is comprised of a   sequence of record structures.  Each record contains drawing   commands, object definitions, and configuration settings.  When a   metafile is processed, the image can be rendered on a display, output   to a printer or plotter, stored in memory, or saved to some   persistent storage.  Reflecting the relationship to the Windows   Graphics Device Interface (GDI) API, WMF data is "played" to a   playback device context in the same manner that PostScript content is   treated as an executable program that results in the output of the   original document.   As Microsoft's first 32-bit operating system, Windows NT 3.1   introduced an overhaul to the Windows API ("Win32") and the in-memory   formats upon which those APIs relied.  The Enhanced Metafile (EMF)   format was created at this time, using 32-bit values instead of WMF's   16-bit values.  In Windows XP, Microsoft extended EMF with "EMF+",   adding support for Windows GDI+.   Many implementations of WMF and EMF were created because of Windows'   commercial success in the 1990s.  A large body of free and   commercially available clip art and other artwork exists in this   format.  Furthermore, WMF content appears non-normatively in certainLeonard                       Informational                     [Page 2]

RFC 7903                Windows Image Media Types         September 2016   standards (e.g., [OOXML]); the usage is common enough that an   implementer would almost certainly need to support it for basic   interoperability.   Microsoft publicly documented the WMF format as early as the 1992   Windows 3.1 SDK.  Since 2007, Microsoft has released the format   specifications [MS-WMF], [MS-EMF], and [MS-EMF+] under its Open   Specification Promise [MS-OSP].1.2.  Windows Bitmaps   Long before the invention of Portable Network Graphics (PNG),   Microsoft Corporation and IBM Corporation needed to record images in   a format that their applications and operating systems could easily   render on low-end machines (Intel 80286).  The resulting "BMP" format   contains a single raster graphic with basic header fields that can be   easily mapped (or "blitted") to locations in memory.  As computing   moved from 16-bit to 32-bit, BMP evolved to contain 32-bit   structures.  As the '90s wore on, the venerable BMP got boosts with   support for additional color spaces, color profiles, and compression   formats.  The same basic format can be used to convey 2-bit black-   and-white bitmaps with a 1-bit alpha mask from the '80s, and full-   color Ultra HD images on leading-edge displays.  BMP is a building   block of other formats, including Windows Metafiles, Windows Icons,   and Windows Cursors.   Many implementations of BMP were created because of Windows'   commercial success in the 1990s.  Usage of the format for interchange   has declined since the advent of PNG (for lossless raster graphics)   and JPEG (for lossy raster graphics); however, a large body of free   and commercially available BMP artwork exists.  Since Windows Icons   are a building block of "favicon.ico" web technology, an implementer   would almost certainly need to support this format for basic   interoperability.   Microsoft publicly documented the BMP format as early as the 1992   Windows 3.1 SDK (in the Windows Metafile documentation).  Since 2007   Microsoft has released the format specification [MS-WMF], which   includes most components of the Windows Bitmap format, under its Open   Specification Promise [MS-OSP].  See Section 2.2.2.9 of [MS-WMF]   (DeviceIndependentBitmap Object).  BMP data begins with a   BITMAPFILEHEADER and is followed by one of the bitmap headers   (BITMAPINFOHEADER, BITMAPV4HEADER, or BITMAPV5HEADER), optional color   table data, bitmap data, and optional profile data, in that order   [BMPSTOR].Leonard                       Informational                     [Page 3]

RFC 7903                Windows Image Media Types         September 2016   Implementers need to be aware of the [MICE] vulnerability, and to   guard against it.  Some details are included in the completed   registration template.2.  Windows Metafile Media Type Registration Application   Type name: image   Subtype name: wmf   Required parameters: None.   Optional parameters:      DEFAULT_CHARSET: The character set intended when the CharacterSet         enumeration (see the WMF specification) specifies         DEFAULT_CHARSET.  The value of this parameter is a charset from         the IANA "Character Sets" registry         <http://www.iana.org/assignments/character-sets>.  When this         parameter is not specified, DEFAULT_CHARSET has the following         meaning in the WMF specification: "a character set based on the         current system locale; for example, when the system locale is         United States English, the default character set is         ANSI_CHARSET" (which is Windows-1252, more or less).  That is,         when not specified, the default character set is system         dependent.  This optional parameter is new to this registration         and may not enjoy widespread support for some time.  Therefore,         EMF instead of WMF (or if necessary under the circumstances,         embedded EMF within WMF) is a more sensible choice when text is         present.   Encoding considerations: Binary.   Security considerations:      The Windows Metafile format's security history is punctuated in      2005-2006 with the disclosure of the Metafile Image Code Execution      ("MICE") vulnerability.  MICE won the 2007 Pwnie Award for "Mass      0wnage" and "Breaking the Internet".  The official Microsoft      security bulletin describes that the flaw occurs because Windows      Metafiles can set the SETABORTPROC value of the MetafileEscapes      enumeration (accessible via the META_ESCAPE record), allowing for      arbitrary code execution, i.e., "active content".      Windows Metafiles can contain Enhanced Metafiles using the      META_ESCAPE_ENHANCED_METAFILE record; thus, the security      considerations of EMF apply to WMF.Leonard                       Informational                     [Page 4]

RFC 7903                Windows Image Media Types         September 2016      Windows Metafiles are historically very buggy.  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.  WMF implementations not backed by Windows GDI      have different risks: namely, while a malicious WMF author may not      consider the non-Windows GDI implementation as a primary target,      WMF 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.      As a "basic" image format, the image/wmf media type does not      employ executable content and provides no facilities for privacy      or integrity.   Interoperability considerations:      Windows Metafile is the original 16-bit metafile format; it was      released in 1990 at what some computer historians might consider      the "zenith" of the desktop publishing revolution.  Accordingly,      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).  For example, references to WMF content appear (non-      normatively) in Office Open XML.  To say that support for this      format is necessary for interoperability would not be an      understatement.      Accommodations for comments or arbitrary data storage in Windows      Metafiles are virtually non-existent.  However, Windows Metafiles      can contain Enhanced Metafiles using the      META_ESCAPE_ENHANCED_METAFILE record, so an implementation that      handles Windows Metafiles is also expected to handle enhanced      metafile content.  Windows Metafiles can store and output text      strings (see META_TEXTOUT and META_EXTTEXTOUT records), but the      encodings of the strings may be ambiguous.  Unicode encodings are      not possible without the DEFAULT_CHARSET parameter defined in this      registration.      The previously unregistered type image/x-wmf is also in wide use.      Accordingly, it is registered as a deprecated alias.   Published specification:      WMF: Microsoft Corporation, "[MS-WMF]: Windows Metafile Format",      v20160714 (Rev 13.1), July 2016,      <http://msdn.microsoft.com/library/cc250370>.Leonard                       Informational                     [Page 5]

RFC 7903                Windows Image Media Types         September 2016   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-wmf      Magic number(s): D7 CD C6 9A (little-endian DWORD 0x9AC6CDD7)      File extension(s): .wmf      Macintosh file type code(s):         None.  A uniform type identifier (UTI) of "com.microsoft.wmf"         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? No3.  Enhanced Metafile Media Type Registration Application   Type name: image   Subtype name: emf   Required parameters: None.   Optional parameters: None.   Encoding considerations: Binary.Leonard                       Informational                     [Page 6]

RFC 7903                Windows Image Media Types         September 2016   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).Leonard                       Informational                     [Page 7]

RFC 7903                Windows Image Media Types         September 2016      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)Leonard                       Informational                     [Page 8]

RFC 7903                Windows Image Media Types         September 2016      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? No4.  Windows Bitmap Media Type Registration Application   Type name: image   Subtype name: bmp   Required parameters: None.   Optional parameters: None.   Encoding considerations: Binary.   Security considerations:      Bitmaps have a mostly unremarkable security history.      Because BMP data can encapsulate JPEG or PNG data (BI_JPEG, BI_PNG      values of the Compression enumeration inSection 2.1.1.7 of the      WMF specification), the security considerations of JPEG and PNG      processing may also apply to BMP.      As a "basic" image format, the image/bmp media type does not      employ executable content and provides no facilities for privacy      or integrity.   Interoperability considerations:      Uncompressed Windows Bitmaps can be rather large.  If there is a      need to compress an image, modern applications should consider      emitting JPEG or PNG data instead of embedding them in BMP      payloads.Leonard                       Informational                     [Page 9]

RFC 7903                Windows Image Media Types         September 2016   Published specification:      WMF: Microsoft Corporation, "[MS-WMF]: Windows Metafile Format",      v20160714 (Rev 13.1), July 2016,      <http://msdn.microsoft.com/library/cc250370>.      BMP: Microsoft Corporation, "Bitmap Storage", MSDN ID dd183391,      <http://msdn.microsoft.com/library/dd183391>.   Applications that use this media type:      Office productivity applications; clip art applications; desktop      publishing applications; web browsers; graphics processing      applications.   Fragment identifier considerations: None.   Additional information:      Magic number(s):         42 4D ("BM"), meaning "bitmap".  The next field         (BITMAPFILEHEADER bfSize) is a little-endian DWORD indicating         the size of the bitmap content in bytes.      File extension(s): .bmp, .dib      Macintosh file type code(s):         "BMP ", "BMPf", or "BMPp".  Apple has promulgated a uniform         type identifier (UTI) of "com.microsoft.bmp".   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? NoLeonard                       Informational                    [Page 10]

RFC 7903                Windows Image Media Types         September 20165.  IANA Considerations   IANA has registered the media types image/wmf, image/x-wmf,   image/emf, image/x-emf, and image/bmp in the standards tree using the   applications provided in Sections2,3, and4 of this document.6.  Security Considerations   See the registration templates for their respective security   considerations.   The Metafile Image Code Execution (MICE) vulnerability won the 2007   Pwnie Award for "Mass 0wnage" and "Breaking the Internet" [PWNIES07].7.  References7.1.  Normative References   [BMPSTOR]  Microsoft Corporation, "Bitmap Storage", MSDN ID dd183391,              <http://msdn.microsoft.com/library/dd183391>.   [MS-EMF]   Microsoft Corporation, "[MS-EMF]: Enhanced Metafile              Format", v20160714 (Rev 12.0), July 2016,              <http://msdn.microsoft.com/library/cc230514>.   [MS-EMF+]  Microsoft Corporation, "[MS-EMFPLUS]: Enhanced Metafile              Format Plus Extensions", v20160714 (Rev 14.1), July 2016,              <http://msdn.microsoft.com/library/cc230724>.   [MS-WMF]   Microsoft Corporation, "[MS-WMF]: Windows Metafile              Format", v20160714 (Rev 13.1), July 2016,              <http://msdn.microsoft.com/library/cc250370>.7.2.  Informative References   [MICE]     Microsoft Corporation, "Vulnerability in Graphics              Rendering Engine Could Allow Remote Code Execution              (912919)", MS06-001, V1.0, January 2006,              <https://technet.microsoft.com/library/security/ms06-001>.   [MS-OSP]   Microsoft Corporation, "Open Specification Promise",              February 2007, <https://msdn.microsoft.com/en-us/openspecifications/dn646765>.   [OOXML]    Ecma International, "Office Open XML File Formats",              Standard ECMA-376, Fourth Edition, ISO/IEC 29500, December              2012, <http://www.ecma-international.org/publications/standards/Ecma-376.htm>.Leonard                       Informational                    [Page 11]

RFC 7903                Windows Image Media Types         September 2016   [PWNIES07] Pwnie Awards LLC, "Winners of Pwnie Awards 2007", 2007,              <http://pwnies.com/archive/2007/winners/>.Author's Address   Sean Leonard   Penango, Inc.   5900 Wilshire Boulevard   21st Floor   Los Angeles, CA  90036   United States of America   Email: dev+ietf@seantek.com   URI:http://www.penango.com/Leonard                       Informational                    [Page 12]