The goal of this challenge was to exploit the load function in a mostly unmodified Lua interpreter. To make it more interesting, the interpreter and libc were compiled with clangs's control flow integrity protection, as well as numerous other hardening mechanisms. The exploit achieves an arbitrary read/write primitive by faking a string and a table object (through the LOADK opcode with an out-of-bounds index), then gains code execution by overwriting a jmpbuf structure used by the interpreter for exception handling and coroutine yielding.
A working exploit can be found in exploit/. Usage:
./pwn.py cat pwn.lua | nc ...