3.1.2
=====

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 (:cve:`CVE-2016-3076`).

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

.. code-block:: c

    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::

    RGBARGBARGBA....

into::


    RRR.
    GGG.
    BBB.
    AAA.


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.