exif.c in the Exif extension in PHP before 5.3.6 on 64-bit platforms performs an incorrect cast, which allows remote attackers to cause a denial of service (application crash) via an image with a crafted Image File Directory (IFD) that triggers a buffer over-read.
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.