OAK — OnChain Attack Knowledge

Worked example · 2023-20

ERC-4337 Paymaster Griefing and DoS Attack Surface Cohort — 2023–2026

OAK Techniques observed
OAK-T13.001, OAK-T13.001.004
Attribution
unattributed (aggregate cohort).
Loss
Aggregate undocumented at class level (griefing attacks are cost-imposition rather than direct extraction; per-paymaster drawdown from sustained griefing campaigns is measured in ETH gas costs rather than stolen funds). The structural loss is in paymaster-operational continuity — a paymaster forced offline by griefing breaks the sponsorship path for legitimate users of the protocol the paymaster serves.
Key teaching point
Paymaster griefing (T13.001.004) is structurally unique among OAK Techniques because the attacker's goal is cost-imposition rather than value extraction. The attacker submits UserOps designed to drain the paymaster's deposited balance without producing useful protocol activity — the funds are burned as gas, not redirected to the attacker. The technique is the ERC-4337 counterpart to network-layer DoS: the paymaster is the resource, the UserOp is the packet, and the EntryPoint's gas accounting is the protocol the attacker exploits. From a defender's perspective, paymaster-griefing is a standing surface for any paymaster whose deposit balance is large enough to be worth disrupting and whose sponsorship criteria are loose enough to admit griefing UserOps.

Summary

Timeline

2023 (ERC-4337 EntryPoint v0.6 deployment — initial paymaster architecture) → 2023–2024 (EntryPoint v0.7 — unused-gas-penalty mechanism added specifically to address paymaster-DoS surface, but early implementation omitted the penalty from postOp value calculation) → 2025 (sustained griefing campaigns observed against production paymasters; Pimlico/Stackup/Alchemy bundler-reputation throttling events) → 2026 (EntryPoint v0.9 — temporary-revert griefing vector closed; [projecteleven2026v09] disclosure).

T13.001.004 — Paymaster Griefing

Three worked sub-patterns documented in the EntryPoint specification and audit literature:

  • (i) Unused-gas-penalty abuse. Artificially-high gas-limit submission triggers an unused-gas-penalty path the paymaster did not budget for. The v0.7 "unused gas penalty" mechanism was itself added to address paymaster-DoS surface, and an early implementation neglected to include the penalty in the value passed to postOp, causing the paymaster to charge users less than the gas it actually had to pay [erc4337spec].
  • (ii) Temporary-revert griefing. A temporary "must-revert" condition in a target contract forces a victim's correctly-signed UserOp to execute while the condition is active — the UserOp validates normally, but the inner call reverts and the paymaster still pays the gas. The EntryPoint v0.9 griefing-vector fix in 2026 addressed exactly this class [projecteleven2026v09].
  • (iii) Bundle-level griefing. A single malicious UserOp causes validatePaymasterUserOp to fail for the rest of the bundle, exhausting the paymaster's bundler-reputation budget and causing the bundler to throttle the paymaster [ozaa4337audit].

Canonical incidents:

  • 2025-04 — ERC-4337 paymaster exploitation incident. See examples/2025-04-erc4337-paymaster.md.
  • 2025-09 — EntryPoint v0.9 griefing-vector disclosure. See examples/2025-09-erc4337-entrypoint-v09-griefing-disclosure.md.
  • 2026-04 — Mass bundler-DoS via paymaster griefing. See examples/2026-04-erc4337-paymaster-griefing-mass-bundler-dos.md.

Detection primitives: paymaster-fund-balance monitoring (drawdown rate exceeding expected sponsorship-throughput envelope); sponsored-UserOp gas-limit anomaly detection (spikes in verificationGasLimit/callGasLimit/paymasterPostOpGasLimit); bundler-reputation-score monitoring at major bundlers (Pimlico, Stackup, Alchemy, Biconomy).

The structural constraint on T13 coverage is ERC-4337 deployment youth: the EntryPoint was first deployed on Ethereum mainnet in 2023 (v0.6), and the paymaster ecosystem is substantially younger than the DeFi lending/AMM/oracle surfaces that dominate T9 coverage. The v0.7→v0.8→v0.9 EntryPoint evolution is the mechanism by which paymaster-griefing surfaces are being closed at the protocol layer — each version increment addresses a specific griefing vector, analogous to how ERC-20 wrapper standards (WETH, Permit2) addressed token-approval surfaces over multiple years.

Public references

  • [erc4337spec] — ERC-4337 EntryPoint specification (v0.6 through v0.9)
  • [projecteleven2026v09] — Project Eleven EntryPoint v0.9 griefing-vector disclosure (2026)
  • [ozaa4337audit] — OZ AA-4337 audit findings (paymaster-DoS surface characterisation)
  • [pimlico2025bundler] — Pimlico bundler reputation-system documentation
  • [stackup2025bundler] — Stackup bundler operations and reputation throttling

Techniques demonstrated (2)