Attack Surfaces in Blockchain Ecosystems BDC Practice Questions (Page 2)

Questions 6–10

1. 6foundation · easy

   Which of the following is a social engineering vector that targets blockchain participants?

   • AA fake customer support agent asking for a user's seed phrase to 'verify' their wallet
   • BA 51% attack on a proof-of-work blockchain
   • CA smart contract that has an integer overflow vulnerability
   • DA network-level eclipse attack that isolates a node
   Reveal Solution Discussion Select an answer first
2. 7application · medium

   A smart contract for a token sale uses a `withdraw` function that sends Ether to the caller after updating the user's balance. An auditor warns that the contract is vulnerable to reentrancy. What is the most effective fix?

   • AUse a reentrancy guard (e.g., a mutex) that prevents reentrant calls, and update the user's balance before making the external call.
   • BIncrease the gas limit for the withdraw function to ensure the external call completes before the balance update.
   • CMake the withdraw function `payable` to allow the contract to receive Ether during the call.
   • DUse `tx.origin` to verify the caller's identity before allowing the withdrawal.
   Reveal Solution Discussion Select an answer first
4. 8expert · hard

   A proof-of-work blockchain has a relatively low hash rate, and a large mining pool controls 48% of the network's hash power. The pool's operators are considering an attack to double-spend a large transaction. They have the ability to temporarily rent additional hash power from a cloud service. What is the most critical factor that determines whether a 51% attack is feasible?

   • AThe cost of renting enough hash power to exceed 50% and maintain it for the duration of the attack, compared to the potential profit from the double-spend.
   • BThe block time, because a faster block time makes it easier to reorganize the chain.
   • CThe number of nodes in the network, because a 51% attack requires controlling a majority of nodes.
   • DThe number of confirmations required by the receiving party, because more confirmations make the attack harder.
   Reveal Solution Discussion Select an answer first
5. 9foundation · easy

   What is a governance attack in a blockchain ecosystem?

   • AAn attacker sends a phishing email to a governance token holder
   • BAn attacker manipulates the voting process to pass malicious proposals or gain control of the protocol
   • CAn attacker exploits a smart contract bug to steal funds
   • DAn attacker launches a DDoS attack on the network's RPC endpoints
   Reveal Solution Discussion Select an answer first
6. 10application · medium

   A DAO is voting on a proposal to upgrade its smart contract. A group of token holders colludes to vote in favor of the proposal, but they do not actually understand the technical implications. The proposal passes, and the upgrade introduces a critical vulnerability that drains the treasury. What type of attack is this?

   • ASybil attack on the network
   • BGovernance attack through uninformed voting
   • CPhishing attack on the DAO's members
   • DEclipse attack on the DAO's nodes
   Reveal Solution Discussion Select an answer first