Solidity Solidity Security and Vulnerabilities

Question 1

Which attack exploits a contract that calls an external contract before updating its state?

Accepted Answer

Reentrancy attack

Answer

A reentrancy attack occurs when an external contract repeatedly calls back into the vulnerable contract before the original function finishes updating its state.

Question 2

What is the recommended pattern to prevent reentrancy attacks in Solidity?

Accepted Answer

Checks-Effects-Interactions pattern

Answer

The Checks-Effects-Interactions pattern requires you to perform all state changes (effects) before calling external contracts (interactions), preventing reentrancy.

Question 3

What Solidity modifier from OpenZeppelin prevents reentrancy by locking the function?

Accepted Answer

nonReentrant

Answer

The `nonReentrant` modifier from OpenZeppelin's ReentrancyGuard sets a flag that reverts any recursive calls into the same function.

Question 4

Which vulnerability allows an attacker to manipulate transaction ordering to their advantage?

Accepted Answer

Front-running (MEV)

Answer

Front-running (Miner Extractable Value) lets attackers observe pending transactions and submit their own transactions with higher gas fees to execute first.

Question 5

What is the danger of using `tx.origin` for authentication in Solidity?

Accepted Answer

It can be spoofed via phishing contracts to impersonate users

Answer

A malicious contract can trick a user into calling it, then use `tx.origin` (the original EOA) to pass authentication checks in a target contract.

Solidity Practice Test

Solidity Practice Test

Solidity Solidity Security and Vulnerabilities