Integer signedness error in bspatch.c in bspatch in bsdiff, as used in Apple OS X before 10.11.6 and other products, allows remote attackers to execute arbitrary code or cause a denial of service (heap-based buffer overflow) via a crafted patch file.
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.