What Role Does the CALL Opcode Play in Enabling Reentrancy?
The CALL opcode in the Ethereum Virtual Machine (EVM) is used to execute a message call to an external contract. When a contract sends Ether to another address, it uses a form of the CALL opcode.
Crucially, this opcode temporarily transfers control flow to the recipient contract. If the recipient is a malicious contract, it can use this moment of control to call back into the original contract's vulnerable withdrawal function, initiating the Reentrancy attack before the state is updated.
Glossar
Message Call
Trigger ⎊ A Message Call, within cryptocurrency and derivatives markets, represents a pre-defined event initiating automated trading instructions; its function extends beyond simple order execution, often incorporating complex conditional logic based on real-time market data.
Reentrancy Attack
Exploit ⎊ The reentrancy attack, a critical vulnerability in smart contracts and financial systems, leverages recursive function calls to circumvent intended security protocols.
Ethereum Virtual Machine
Computation ⎊ The Ethereum Virtual Machine (EVM) functions as a decentralized, Turing-complete computational engine, central to the execution of smart contracts on the Ethereum blockchain.
Call Opcode
Execution ⎊ A Call Opcode, within cryptocurrency derivatives, signifies a programmatic instruction to initiate a long position contingent upon an underlying asset exceeding a predetermined strike price, fundamentally altering risk exposure.
Transaction Atomicity
Finality ⎊ In the context of cryptocurrency, options trading, and financial derivatives, finality refers to the assurance that a transaction, once confirmed, cannot be reversed or altered.