ImageMagick vulnerable to denial of service via integer overflow in BMP decoder on 32-bit systems

ImageMagick is an open source software suite for displaying, converting, and editing raster image files. In ImageMagick versions prior to 7.1.2-7 and 6.9.13-32, an integer overflow vulnerability exists in the BMP decoder on 32-bit systems. The vulnerability occurs in coders/bmp.c when calculating the extent value by multiplying image columns by bits per pixel. On 32-bit systems with size_t of 4 bytes, a malicious BMP file with specific dimensions can cause this multiplication to overflow and wrap to zero. The overflow check added to address CVE-2025-57803 is placed after the overflow occurs, making it ineffective. A specially crafted 58-byte BMP file with width set to 536,870,912 and 32 bits per pixel can trigger this overflow, causing the bytes_per_line calculation to become zero. This vulnerability only affects 32-bit builds of ImageMagick where default resource limits for width, height, and area have been manually increased beyond their defaults. 64-bit systems with size_t of 8 bytes are not vulnerable, and systems using default ImageMagick resource limits are not vulnerable. The vulnerability is fixed in versions 7.1.2-7 and 6.9.13-32.