/usr/lib/x86_64-linux-gnu/libcext.so is in libcext-dev 7.1-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libcext.so.0.2.2
/usr/lib/x86_64-linux-gnu/libcext.so.0.2.2