FREE Blockchain Security Training Smart Contract Vulnerabilities Questions and Answers

Question 1

A smart contract function updates a user's balance *after* making an external call to send them funds. Which vulnerability is most likely to be exploited in this scenario?

Accepted Answer

Reentrancy

Answer

Integer Overflow

Answer

Front-Running

Answer

Unchecked External Call

Question 2

A developer is creating a token contract. To save gas, they use the `uint8` data type for user balances. What potential vulnerability should the developer be most concerned about when users transfer large numbers of tokens?

Accepted Answer

Integer Overflow/Underflow

Answer

Denial of Service

Answer

Access Control Violation

Answer

Insecure Randomness

Question 3

An attacker observes a large pending transaction in the mempool to buy a specific token on a decentralized exchange. The attacker quickly submits their own 'buy' transaction for the same token with a higher gas fee, followed by a 'sell' transaction. What is this type of attack called?

Accepted Answer

Front-Running

Answer

Reentrancy

Answer

Time-locking Attack

Answer

Integer Underflow

Question 4

A smart contract has a function that iterates through an array of investor addresses to distribute dividends. An attacker adds thousands of new addresses to this array, causing the transaction to always fail due to exceeding the block gas limit. Which vulnerability has been exploited?

Accepted Answer

Denial of Service (DoS)

Answer

Unchecked External Call

Answer

Integer Overflow

Answer

Short Address Attack

Question 5

Which of the following is the BEST mitigation strategy against reentrancy attacks in Solidity?

Accepted Answer

Implementing the Checks-Effects-Interactions pattern.

Answer

Using the `transfer()` function for all Ether transactions.

Answer

Ensuring all functions have the `payable` modifier.

Answer

Storing all user balances in private mappings.

Question 6

A smart contract sends an important token reward to a user's address using a low-level `.call()` function but does not verify the boolean value returned by the call. Why is this a security risk?

Accepted Answer

The contract may proceed as if the call succeeded, even if it failed.

Answer

The transaction will always fail due to insufficient gas.

Answer

It can lead to a Denial of Service attack.

Answer

It allows for front-running the reward distribution.

Blockchain Security Training FREE Blockchain Security Training Smart Contract Vulnerabilities Questions and Answers

A smart contract function updates a user's balance after making an external call to send them funds.
Which vulnerability is most likely to be exploited in this scenario?

A smart contract function updates a user's balance *after* making an external call to send them funds.Which vulnerability is most likely to be exploited in this scenario?

A smart contract function updates a user's balance after making an external call to send them funds.
Which vulnerability is most likely to be exploited in this scenario?