Attack Surfaces in Blockchain Ecosystems BDC Practice Questions (Page 5)

Questions 21–25

1. 21application · medium

   A proof-of-stake blockchain is concerned about an attacker who could acquire a large amount of the cryptocurrency by purchasing it on exchanges, then use that stake to rewrite history from a point before the purchase. Which attack is this, and what is a common defense?

   • AEclipse attack; use more peers per node.
   • B51% attack; increase the block time to make attacks harder.
   • CSybil attack; require proof-of-work for validators.
   • DLong-range attack; use checkpointing or finality gadgets.
   Reveal Solution Discussion Select an answer first
2. 22application · medium

   A blockchain project's community uses a forum to discuss proposals. An attacker creates multiple fake accounts to post positive comments about a proposal and downvote opposing views. The attacker also sends direct messages to influential community members, pretending to be a developer, to gain their support. What type of attack is this?

   • ADDoS attack
   • BEclipse attack
   • CSelfish mining attack
   • DSocial engineering and Sybil attack combined
   Reveal Solution Discussion Select an answer first
4. 23application · medium

   A DeFi lending protocol uses a price oracle that reads from a single DEX pool. An attacker notices the pool has low liquidity and uses a flash loan to temporarily skew the price, causing the protocol to allow undercollateralized loans. After the attack, the attacker repays the flash loan and profits. Which combination of mitigations would MOST effectively reduce the risk of this specific attack?

   • AIncrease the protocol's collateral factor and require a longer loan duration for all borrowers.
   • BAdd a reentrancy guard to the loan function and restrict flash loan usage to whitelisted addresses.
   • CDeploy the protocol on a private blockchain with a smaller set of validators.
   • DUse a time-weighted average price (TWAP) oracle and add a maximum price deviation check between the oracle and a secondary reference.
   Reveal Solution Discussion Select an answer first
5. 24application · medium

   A blockchain network's nodes are being overwhelmed with a high volume of invalid transactions and connection requests, causing legitimate transactions to be delayed. The network's block production has slowed, and some nodes are becoming unreachable. Which type of attack is being performed, and what is a common mitigation?

   • A51% attack; increase the block size to accommodate more transactions.
   • BSybil attack; require proof-of-work for every node.
   • CSelfish mining; add more nodes to the network.
   • DDDoS attack; rate-limit incoming connections and use traffic filtering.
   Reveal Solution Discussion Select an answer first
6. 25application · easy

   A blockchain network's nodes are being flooded with a high volume of invalid transactions, causing the network to slow down and legitimate transactions to be delayed. The attack does not target any specific node but aims to overwhelm the network's capacity. What type of attack is this?

   • ASybil attack
   • BSelfish mining attack
   • CDistributed denial-of-service (DDoS) attack
   • DEclipse attack
   Reveal Solution Discussion Select an answer first