Two Attacks On Proof-of-Stake GHOST/Ethereum

TL;DR

This paper identifies two vulnerabilities in Ethereum's Proof-of-Stake protocol, showing how adversaries can manipulate the chain through equivocation and exploiting protocol features, challenging its security assumptions.

Contribution

The paper introduces two novel attacks on Ethereum's PoS consensus, revealing fundamental incompatibilities and vulnerabilities in the current protocol design.

Findings

PoS allows adversaries to produce unlimited equivocating blocks.

Orphaned uncle blocks influence fork choice under GHOST, enabling control.

LMD can be exploited to perform a balancing attack.

Abstract

We present two attacks targeting the Proof-of-Stake (PoS) Ethereum consensus protocol. The first attack suggests a fundamental conceptual incompatibility between PoS and the Greedy Heaviest-Observed Sub-Tree (GHOST) fork choice paradigm employed by PoS Ethereum. In a nutshell, PoS allows an adversary with a vanishing amount of stake to produce an unlimited number of equivocating blocks. While most equivocating blocks will be orphaned, such orphaned `uncle blocks' still influence fork choice under the GHOST paradigm, bestowing upon the adversary devastating control over the canonical chain. While the Latest Message Driven (LMD) aspect of current PoS Ethereum prevents a straightforward application of this attack, our second attack shows how LMD specifically can be exploited to obtain a new variant of the balancing attack that overcomes a recent protocol addition that was intended to mitigate balancing-type attacks. Thus, in its current form, PoS Ethereum without and with LMD is vulnerable to our first and second attack, respectively.