I observed that my system is vulnerable to remote OS command injector attack. What would be the impact of Remote OS command injector attack?
If a bad guy can persuade you to run his program on your computer, it's not solely your computer anymore.
The question pretty much answeres itself: The attack can run code on your machine allowing him to run any malware. There are a few boundaries for hackers like the size of the code to be executed or the privileges to malware is run with, however, hackers have overcome this problems with various techniques like small "loaders" which make space for a bigger malware to come and then download it or exploits to bypass privilege restrictions etc.
To make use of the quote above, being able to run a program without restrictions can lead to pretty much everything from stealing your passwords and banking information to holding your PC ransom or destroying it.