libffi, a library used to call code written in one language from code written in a different language, was enforcing an executable stack on the i386 architecture. While this might not be considered a vulnerability by itself, this could be leveraged when exploiting other vulnerabilities, like for example the stack clash class of vulnerabilities discovered by Qualys Research Labs. For the full details, please refer to their advisory published at: https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt