bug#27329: Emacs 25.2.1 M-x list-packages crashes on https://melpa (SSL problem ?)
I cannot reproduce the problem on my somewhat-different platform (Ubuntu 16.04.2
LTS, x86-64, configured --with-ns so that Emacs reports "NS gnustep-gnu-0.24.0"
as the UI). Assuming you still have the problem, can you please build Emacs with
CFLAGS='-g3 -O0', run Emacs under GDB, and send a backtrace of the crash?