Remote Code Execution via Python __import__() - MMACTF 2016 Tsurai Web 300 writeup - 
https://blog.0daylabs.com/2016/09/05/code-execution-python-import-mmactf-300/

Original writeup (https://blog.0daylabs.com/2016/09/05/code-execution-python-import-mmactf-300/).