A buffer overflow error was found in the POSIX unit's procedures
process-execute and process-spawn.  The code allocated a buffer
of size ARG_MAX for the argument array, and ENV_MAX for the
environment array, then copied the strings from the input lists
into that buffer *without* checking the length of the lists.

On modern Linuxen, ARG_MAX and ENV_MAX are both undefined, which
exacerbated the problem: CHICKEN would fall back to 256 for ARG_MAX
and 1024 for ENV_MAX when these were undefined.

Additionally, a memory leak existed in this code, which would be
triggered when an error is raised during argument and environment
processing (e.g., if one of the arguments wasn't a string).

References:

http://seclists.org/oss-sec/2016/q3/276