The vulnerability exploited by attacks that instantaneously manipulate exchange rates using flash loans and trigger mass liquidations is known as Price Oracle Manipulation.
In a flash loan attack, a cyber thief takes out a flash loan (a form of uncollateralized lending) from a lending protocol and uses it in conjunction with various types of gimmickry to manipulate the market in their favor. These attacks can occur in mere seconds and yet still involve four or more DeFi protocols