Definition
A bribery attack is a security risk in blockchain systems where an external party offers side payments to validators or block producers to induce them to violate the protocol’s intended consensus rules. Instead of relying solely on on-chain incentives, the attacker uses off-chain bribes to make dishonest behavior temporarily more profitable than honest participation. This can target the consensus layer directly or be coordinated around specific blocks or time windows to alter expected outcomes. The attack exploits the economic assumptions that underpin the security of the network rather than its cryptography.
In a bribery attack, the attacker typically proposes conditional rewards that depend on validators participating in a specific chain history or block ordering. These incentives can be designed to encourage behaviors such as participating in a reorg, censoring certain transactions, or supporting particular governance outcomes. Because the bribes are external to the protocol, they may not be visible to other participants and are not captured by standard on-chain security models. The feasibility of such attacks depends on validator concentration, coordination costs, and the relative size of the bribe compared to normal protocol rewards and penalties.
Context and Usage
Bribery attacks are often discussed in the context of consensus security, where the economic incentives of validators are assumed to align with honest behavior. By introducing additional off-protocol rewards, an attacker attempts to break this alignment and make deviations from the canonical chain rational for some participants. In systems with strong slashing or lockup mechanisms, the bribe must exceed not only expected rewards but also potential penalties, which shapes how the risk is modeled. The concept is closely related to the broader analysis of game-theoretic vulnerabilities in permissionless networks.
This type of attack can intersect with MEV, governance, and reorg risks when bribes are structured around specific ordering or inclusion of transactions, or around particular voting outcomes. For example, a bribery attack might target validators to support a coordinated reorg that captures MEV or reverses finalized-looking transactions. In governance settings, bribes can be offered to influence validator or delegate behavior in protocol-level decisions without directly attacking the consensus mechanism itself. As a result, bribery attacks are treated as a systemic risk that must be considered in both protocol design and incentive modeling.