hardened_malloc is a hardened memory allocator made by Daniel Micay that protects against many memory corruption vulnerabilities. According to the project's description:
Obscurix uses this for many applications by default. It changes the LD_PRELOAD variable to point to /usr/lib/libhardened_malloc.so using bubblewrap's --setenv flag or systemd's Environment option.
Obscurix doesn't use it as the system default memory allocator as many things can break with it such as Xorg. It can be added as the default by adding its file path to /etc/ld.so.preload or building it into libc directly.