Blockchain Developer Security Principles

Question 1

A reentrancy attack on a smart contract is best mitigated by which design pattern?

Accepted Answer

Checks-effects-interactions pattern

Answer

Updating state before making external calls prevents an attacker's fallback from re-entering and draining funds.

Question 2

Which Solidity construct provides reentrancy protection by locking a function during execution?

Accepted Answer

nonReentrant modifier with a mutex

Answer

A nonReentrant modifier uses a boolean mutex to block recursive calls into the same function.

Question 3

Integer overflow vulnerabilities in older Solidity were commonly prevented using which library?

Accepted Answer

SafeMath

Answer

SafeMath wrapped arithmetic to revert on overflow before Solidity 0.8 made checks built-in.

Question 4

From Solidity 0.8.0 onward, how is integer overflow handled by default?

Accepted Answer

Arithmetic reverts automatically on overflow/underflow

Answer

Solidity 0.8+ includes built-in overflow/underflow checks that revert the transaction.

Question 5

A front-running attack exploits which property of public blockchains?

Accepted Answer

Pending transactions are visible in the mempool before mining

Answer

Attackers observe pending transactions in the mempool and submit their own with higher gas to execute first.

Blockchain Practice Test