/usr/lib/x86_64-linux-gnu/libgladeui-2.so is in libgladeui-dev 3.20.0-2+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgladeui-2.so.6.3.0
/usr/lib/x86_64-linux-gnu/libgladeui-2.so.6.3.0