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]$