Transaction fee markets and mempool heuristics determine which transactions are considered high priority. When adversaries deliberately distort those signals, fee estimation manipulation becomes a lever for selective exclusion. Attackers can inject crafted traffic, alter apparent fee distributions, or withhold timely rebroadcasts so that wallets and relays estimate a victim's transaction as low value and therefore unlikely to be included. That apparent randomness is often an engineered effect rather than noise.
How manipulation enables targeted exclusion
Two channels make this practical. First, deliberate mempool spam can occupy block space and push legitimate transactions below inclusion thresholds, effectively delaying or suppressing users whose transactions coincide with the noise. Philip Daian at Cornell Tech documented how miner extractable value and transaction ordering incentives create environments where actors pay to influence inclusion and ordering of transactions. Second, adversaries can craft fee-profiles that bias common estimation algorithms used by wallets, so particular address patterns or transaction types consistently appear low-priority. Vitalik Buterin at the Ethereum Foundation has described structural incentives around block builders and proposers that can enable selective exclusion when private ordering and builder collusion exist. The combination of adaptive fee heuristics and opaque builder markets creates fertile ground for targeted attacks.
Consequences, context, and real-world nuance
The immediate consequence is degraded availability: affected transactions see long confirmation delays, elevated fees as users rebroadcast with higher prices, or complete non-inclusion when attackers sustain pressure. Financially, victims lose time-sensitive opportunities; legally and politically, targeted communities—dissidents, journalists, or activists in specific territories—can be selectively muted, producing a chilling effect on speech and commerce. In environments where state actors can influence local validators or ISPs, such tactics compound territorial censorship already imposed by networking controls. Environmental costs arise from repeated retransmissions and wasted block space, increasing energy per settled transaction without producing useful throughput.
Mitigations include more robust fee-estimation that resists short-term noise, transparent proposer-builder separation reforms that reduce private exclusion routes, and monitoring by independent researchers and node operators. Philip Daian at Cornell Tech and others have emphasized that addressing the economic incentives—reducing extractable value and improving transparency—is central to reducing the feasibility of fee-manipulation–driven censorship. Complete immunity is difficult; the solution combines protocol, economic, and governance changes.