Blockchain Security Training Network & Node Security 2 — Questions and Answers
Question 1: An attacker isolates a node from the honest network and feeds it a false view of the blockchain. What attack is this?
- Eclipse attack (Correct answer)
- Replay attack
- Dusting attack
- Sybil reorg
Correct answer: Eclipse attack
An eclipse attack monopolizes a victim node's peer connections to control all information it receives.
Question 2: Which practice best mitigates eclipse attacks on a node?
- Diversifying inbound/outbound peers and using anchor connections (Correct answer)
- Increasing block size
- Disabling the mempool
- Lowering the gas limit
Correct answer: Diversifying inbound/outbound peers and using anchor connections
Maintaining diverse peers and persistent anchor connections makes it harder to monopolize a node's connections.
Question 3: What is the primary purpose of a node running behind a firewall exposing only the necessary P2P port?
- Reduce the attack surface for remote exploitation (Correct answer)
- Increase block reward
- Speed up consensus
- Lower transaction fees
Correct answer: Reduce the attack surface for remote exploitation
Limiting exposed ports reduces avenues an attacker can use to reach the node.
Question 4: A full node's RPC interface is exposed to the public internet without authentication. What is the main risk?
- Unauthorized commands, wallet access, or DoS (Correct answer)
- Faster syncing
- Higher staking yield
- Improved peer discovery
Correct answer: Unauthorized commands, wallet access, or DoS
Open RPC endpoints can let attackers query data, drain wallets, or overwhelm the node.
Question 5: Which transport-layer protection helps secure communication between a node and its remote RPC clients?
- TLS encryption with authentication (Correct answer)
- Plaintext HTTP
- Disabling all logging
- Removing the firewall
Correct answer: TLS encryption with authentication
TLS encrypts and authenticates the channel, preventing eavesdropping and tampering.
Question 6: What does a Sybil attack on a peer-to-peer blockchain network involve?
- Creating many fake identities to gain disproportionate influence (Correct answer)
- Double-spending via a 51% hash share
- Forging a single TLS certificate
- Exploiting a smart contract reentrancy bug
Correct answer: Creating many fake identities to gain disproportionate influence
A Sybil attack floods the network with fake nodes to subvert peer selection or consensus signaling.
Question 7: Why is keeping node software updated a critical network-security control?
- Patches fix known vulnerabilities and consensus bugs (Correct answer)
- It increases the token price
- It removes the need for a firewall
- It disables peer discovery
Correct answer: Patches fix known vulnerabilities and consensus bugs
Updates close exploitable security holes and prevent chain splits from outdated consensus rules.
Blockchain Security Training Network & Node Security 2
An attacker isolates a node from the honest network and feeds it a false view of the blockchain.
What attack is this?