/usr/lib/x86_64-linux-gnu/libboost_regex.so is in libboost-regex1.55-dev 1.55.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libboost_regex.so.1.55.0
/usr/lib/x86_64-linux-gnu/libboost_regex.so.1.55.0