ImageMagick ReadSGIImage() Heap Overflow

Overflow.pl Security Advisory #7

ImageMagick ReadSGIImage() Heap Overflow

Vendor: ImageMagick (http://www.imagemagick.org)
Affected version: 6.x up to and including 6.2.8
Vendor status: Fixed version released (6.2.9)

Author: Damian Put <pucik (at) overflow (dot) pl [email concealed]>
URL: http://www.overflow.pl/adv/imsgiheap.txt
Date: 14.08.2006

1. Background

ImageMagick is a free software suite to create, edit, and compose bitmap images.
 It can read, convert and write images in a large variety of formats.

http://www.imagemagick.org

2. Description

Remote exploitation of a heap overflow vulnerability could allow execution of
arbitrary code or couse denial of service.

A heap overflow exists in ReadSGIImage() function, that is used to
decode a SGI image file. The vulnerable code is:

coders/sgi.c:

static Image *ReadSGIImage(const ImageInfo *image_info,ExceptionInfo *exception)
{
...
    iris_info.bytes_per_pixel=(unsigned char) ReadBlobByte(image);
...
    image->columns=iris_info.columns;
    image->rows=iris_info.rows;
...
    bytes_per_pixel=(size_t) iris_info.bytes_per_pixel;
    number_pixels=(MagickSizeType) iris_info.columns*iris_info.rows;
...
    iris_pixels=(unsigned char *)AcquireMagickMemory
(4*bytes_per_pixel*iris_info.columns*iris_info.rows);

We can manipalute iris_info.rows, iris_info.columns and bytes_per_pixel
value. Allocation of memory to "iris_pixels" is based on this values.
When rows*cols*bytes_per_pixe*4 overflow integer variable, we can alloc not
enough memory for next operations, and cause heap overflow.

3. PoC

Example crafted SGI file: http://overflow.pl/poc/imheap.sgi

[pucik@overflow ImageMagick-6.2.8]$ display imheap.sgi
*** glibc detected *** free(): invalid next size (fast): 0x08055dd0 ***
Abort (core dumped) 
[pucik@overflow ImageMagick-6.2.8]$

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