Integer overflow in the ImagingResampleHorizontal function in libImaging/Resample.c in Pillow before 3.1.1 allows remote attackers to have unspecified impact via negative values of the new size, which triggers a heap-based buffer overflow.
https://github.com/python-pillow/Pillow/blob/c3cb690fed5d4bf0c45576759de55d054916c165/CHANGES.rst
https://github.com/python-pillow/Pillow/commit/4e0d9b0b9740d258ade40cce248c93777362ac1e