The Load_SBit_Png function in sfnt/pngshim.c in FreeType before 2.5.4 does not restrict the rows and pitch values of PNG data, which allows remote attackers to cause a denial of service (integer overflow and heap-based buffer overflow) or possibly have unspecified other impact by embedding a PNG file in a .ttf font file.
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.