The Pillow maintainers report:
Pillow 3.1.0 and earlier when linked against libtiff >= 4.0.0 on x64 may overflow a buffer when reading a specially crafted tiff file. Specifically, libtiff >= 4.0.0 changed the return type of TIFFScanlineSize from int32 to machine dependent int32|64. If the scanline is sized so that it overflows an int32, it may be interpreted as a negative number, which will then pass the size check in TiffDecode.c line 236. To do this, the logical scanline size has to be > 2gb, and for the test file, the allocated buffer size is 64k against a roughly 4gb scan line size. Any image data over 64k is written over the heap, causing a segfault. This issue was found by security researcher FourOne.