/usr/lib/x86_64-linux-gnu/libustr-1.0.so is in libustr-dev 1.0.4-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libustr-1.0.so.1
/usr/lib/x86_64-linux-gnu/libustr-1.0.so.1