Eclipse Attack

An eclipse attack is a peer-to-peer network attack that cuts a single blockchain node off from honest peers so the attacker can control what that node sees and sends. By surrounding the target with attacker-controlled connections, the node’s view of the chain can be shaped or delayed.

What the attack tries to achieve

The goal is to isolate one node, not to take over the whole network. Once isolated, the victim can be fed outdated blocks, censored transactions, or false information. That opens the door to follow-on tricks like convincing the node to accept a transaction that will later be reversed, or wasting a miner’s time on blocks that will never make it to the main chain.

How isolation happens in practice

Blockchains limit how many peers a node can connect to at once, so a determined attacker can try to occupy all of those slots with their own nodes. Common tactics include flooding the target with attacker IPs and waiting for (or forcing) a restart so the target reconnects only to those addresses. With all connections monopolized, the attacker filters everything the victim sends or receives.

What makes eclipse attacks possible

Two ingredients help the attacker: a node’s finite connection slots and predictable peer selection. If a node tends to reuse the same neighbors, or draws too many of them from the same place, it becomes easier to ring-fence. These are network-layer issues rather than smart-contract bugs.

Typical fallout

Effects depend on who gets isolated. A mining node may waste hashpower on a fork that the rest of the network will ignore. A regular node might relay or accept transactions that look valid inside the bubble but will later be rejected. In both cases, the victim’s local copy of the ledger can drift away from reality.

Detection and defenses

Defenses revolve around making it hard to capture all of a node’s connections. Practical steps include diversifying peers, rotating and randomly selecting new connections, and avoiding patterns that let an attacker predict which neighbors you will keep. Some guides also point out that improved peer-selection algorithms reduce exposure.