Integer overflow in the gray_render_span function in smooth/ftgrays.c in FreeType before 2.4.0 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted font 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.