CVE-2016-3076 – Buffer overflow in Jpeg2KEncode.c

Pillow between 2.5.0 and 3.1.1 may overflow a buffer when writing large Jpeg2000 files, allowing for code execution or other memory corruption.

This occurs specifically in the function j2k_encode_entry, at the line:

state->buffer = malloc (tile_width * tile_height * components * prec / 8);

This vulnerability requires a particular value for height * width such that height * width * components * precision overflows, at which point the malloc will be for a smaller value than expected. The buffer that is allocated will be ((height * width * components * precision) mod (2^31) / 8), where components is 1-4 and precision is either 8 or 16. Common values would be 4 components at precision 8 for a standard RGBA image.

The unpackers then split an image that is laid out:




If this buffer is smaller than expected, the jpeg2k unpacker functions will write outside the allocation and onto the heap, corrupting memory.

This issue was found by Alyssa Besseling at Atlassian.