Blockchain Developer Security and Vulnerabilities 2

Question 1

A function transfers Ether to a user before updating their balance. What vulnerability does this introduce?

Accepted Answer

Reentrancy

Answer

Integer overflow

Answer

Front-running

Answer

Timestamp dependence

Question 2

Which pattern is the recommended defense against reentrancy attacks?

Accepted Answer

Checks-Effects-Interactions

Answer

Lazy initialization

Answer

Proxy delegation

Answer

Eager evaluation

Question 3

In Solidity 0.8+, what happens by default when an arithmetic operation overflows?

Accepted Answer

The transaction reverts

Answer

The value wraps around

Answer

It returns zero

Answer

It emits a warning

Question 4

What is the main risk of using tx.origin for authorization?

Accepted Answer

A malicious intermediate contract can impersonate the user

Answer

It costs more gas than msg.sender

Answer

It cannot be read in view functions

Answer

It only works for EOAs

Question 5

A lottery contract picks a winner using block.timestamp and blockhash. Why is this insecure?

Accepted Answer

Miners/validators can manipulate these values

Answer

Timestamps are always zero on testnets

Answer

Blockhash is unavailable in Solidity

Answer

It uses too much storage

Question 6

What does the 'pull over push' payment pattern improve?

Accepted Answer

Resilience to failed external transfers and DoS

Answer

Gas refunds on storage clearing

Answer

Faster block confirmation

Answer

Lower contract bytecode size

Question 7

Which tool is commonly used for static analysis of Solidity contracts to detect vulnerabilities?

Accepted Answer

Slither

Answer

Webpack

Answer

Prettier

Answer

Truffle migrate