The vulnerability in hh.exe is already well known and documented by the LOLBAS project [0]. My team and I (Adversary Simulation at IBM X-Force Red) conduct stealth-oriented red team security assessments and we use vulnerabilities like this to do our jobs every day - just as any red team worth its salt would. Capabilities like this are built into all kinds of tools that are installed by default on Windows. They are often essential to obtaining code or command execution on hosts through social engineering or post-exploitation when moving laterally between hosts.
This is just speculation, but the privesc vulnerability might be related to memory allocation in the DLL used to integrate with the system shell context menu - i.e. right clicking on a file. Just a guess based on the mention of a heap overflow.