[NEWS] GIMP Denial Of Service Vulnerability (GIF Zero Width or Height )

From: SecuriTeam (support_at_securiteam.com)
Date: 03/22/05

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      GIMP Denial Of Service Vulnerability (GIF Zero Width or Height )
    ------------------------------------------------------------------------

    SUMMARY

     <http://www.gimp.org/> The GIMP is the GNU Image Manipulation Program. It
    is a freely distributed piece of software for such tasks as photo
    retouching, image composition and image authoring.

    The GIMP gifload plug-in is vulnerable to a denial of service attack when
    it processes some GIF files with image width or height value of 0.

    DETAILS

    Vulnerable Systems:
     * The GIMP 2.2.4 for all Operating Systems. Prior versions may be
    vulnerable as well.

    GIMP use gifload to load GIF files. The gifload does not check the value
    of width and height fields of the image descriptor when reading a GIF
    file. It generate a size to call g_malloc() and it does not check the
    return pointer value from g_malloc() yet before used the pointer. So if
    gifload have a value of 0 from the width or height field read from the
    image descriptor, it crashes.

    Changing any normal GIF file image width value or image height value to 0,
    will cause GIMP to crash when trying to open the image.

    Vulnerable Code:
    source code from gimp-2.2.4/plug-ins/common/gifload.c:
    ..
    // load_image()
    // Didn't check the value of width and height fields in image descriptor
    // when read from file
    ..
    if (!useGlobalColormap)
            {
              if (ReadColorMap (fd, bitPixel, localColorMap, &grayScale))
                {
                  g_message ("Error reading local colormap");
                  return image_ID;
                }
              image_ID = ReadImage (fd, filename, LM_to_uint (buf[4], buf[5]),
                                    LM_to_uint (buf[6], buf[7]),
                                    localColorMap, bitPixel,
                                    grayScale,
                                    BitSet (buf[8], INTERLACE), imageCount,
                                    (guint) LM_to_uint (buf[0], buf[1]),
                                    (guint) LM_to_uint (buf[2], buf[3]),
                                    GifScreen.Width,
                                    GifScreen.Height
                                    );
            }
          else
            {
              image_ID = ReadImage (fd, filename, LM_to_uint (buf[4], buf[5]),
                                    LM_to_uint (buf[6], buf[7]),
                                    GifScreen.ColorMap, GifScreen.BitPixel,
                                    GifScreen.GrayScale,
                                    BitSet (buf[8], INTERLACE), imageCount,
                                    (guint) LM_to_uint (buf[0], buf[1]),
                                    (guint) LM_to_uint (buf[2], buf[3]),
                                    GifScreen.Width,
                                    GifScreen.Height
                                    );
            }
    .
    // ReadImage() len==image width, height==image height
    // xpos and ypos are initialized to 0
    gint xpos = 0, ypos = 0, pass = 0;
    ..
      if (alpha_frame)
        dest = (guchar *) g_malloc (len * height *
                                    (promote_to_rgb ? 4 : 2));
        // dest == 0;
      else
        dest = (guchar *) g_malloc (len * height);
        // dest == 0;
    ..
              if (promote_to_rgb)
                {
                  temp = dest + ( (ypos * len) + xpos ) * 4;
                  // temp = 0 + ( (0 * 0) + 0) * 4;
                  // temp == 0
                  // So it cause write access exception!
                  *(temp ) = (guchar) cmap[0][v];
                  *(temp+1) = (guchar) cmap[1][v];
                  *(temp+2) = (guchar) cmap[2][v];
                  *(temp+3) = (guchar) ((v == Gif89.transparent) ? 0 : 255);
                }
              else
                {
                  temp = dest + ( (ypos * len) + xpos ) * 2;
                  // temp = 0 + ( (0 * 0) + 0) * 2;
                  *temp = (guchar) v;
                  *(temp+1) = (guchar) ((v == Gif89.transparent) ? 0 : 255);
                }
    EOF

    Vender Status:
    The vendor has fixed the bug:
    <http://bugzilla.gnome.org/show_bug.cgi?id=169113>
    http://bugzilla.gnome.org/show_bug.cgi?id=169113

    Disclosure Timeline:
    2005-03-03 Reported To Vendor, And the vendor has fixed the bug.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:felix__zhou@hotmail.com>
    Hongzhen Zhou.

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