An elevation-of-privilege bug allows attackers to run any program on a target machine with high privileges. A researcher has dropped a zero-day vulnerability that affects the Steam game client for Windows. The vulnerability exists in the Steam Client Service, which runs on Windows computers with system privileges. Steam says that it has more than a billion registered users worldwide (and 90 million active users, who sign up to play games like Assassin s Creed, Grand Theft Auto V and Warhammer) Valve then published a patch, that the same researcher said can be bypassed.
Source: https://threatpost.com/gamers-zero-day-steam-client-affects-windows/147225/