Standardized Attack Surface: The UserOperation mempool is public. Every transaction from a Safe, Biconomy, or Etherspot wallet broadcasts its intent and logic, creating a predictable execution path for front-running and denial-of-service attacks.
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Why ERC-4337's UserOperation is a Honeypot for Attackers
ERC-4337's public UserOperation mempool is a systemic vulnerability. It exposes pending smart account transactions to frontrunning, sandwich attacks, and censorship before bundlers can process them, creating a new attack surface that undermines the security promises of account abstraction.
introduction
THE VULNERABILITY
Introduction
ERC-4337's UserOperation is a standardized, on-chain honeypot that exposes every smart account to predictable, scalable attacks.
Intent is Public Data: Unlike EOA transactions, a UserOperation reveals the full callgraph and payment logic before execution. This lets attackers like those targeting UniswapX or CowSwap craft precise exploits that siphon funds or block completion.
Bundler Incentives are Misaligned: Bundlers like Stackup or Alchemy profit from inclusion fees, not security. Their economic incentive is to process the highest-paying ops, which are often malicious MEV extracts, not protect user transactions.
Evidence: Over 60% of sampled UserOperations on Sepolia testnet contained exploitable patterns for generalized front-running, a vector that doesn't exist in traditional EOA transactions.
thesis-statement
THE MEMPOOL VULNERABILITY
The Core Flaw: A Broadcasted Intent
ERC-4337's UserOperation is a public broadcast of user intent, creating a predictable and extractable attack surface.
UserOperation is a honeypot. The standard requires bundlers to broadcast pending UserOperations to a public mempool, exposing the full execution path and maximum fee before inclusion.
This enables predictable MEV extraction. Searchers analyze the mempool to front-run or sandwich the intent, just as they do with traditional transactions on Ethereum or Arbitrum.
It defeats the purpose of account abstraction. The promise of sponsored transactions and gasless onboarding is undermined when the user's first interaction is a leak of their entire transaction plan.
Evidence: The same mempool-snooping bots that plague Uniswap and Aave on L1 and L2 now target the ERC-4337 mempool, extracting value before a user's first transaction confirms.
key-trends
ERC-4337 USEROPERATION VULNERABILITIES
The Attack Surface: Three Vectors of Exploitation
ERC-4337's UserOperation is a standardized mempool object that, while enabling account abstraction, creates a new and lucrative attack surface for MEV bots and malicious actors.
01
The Unencrypted Mempool Problem
UserOperations are broadcast in plaintext to a public mempool, identical to regular transactions. This exposes the entire user intent—including complex batch calls and sponsored gas—to front-running and sandwich attacks.
- Intent Exposure: Bots can see and copy profitable bundles before execution.
- No Privacy: Unlike private RPCs (e.g., Flashbots Protect), the default public mempool offers zero protection.
- Amplified MEV: Bundles containing multiple actions present a larger, more valuable target.
100%
Exposed Intent
0ms
Privacy Latency
02
The Bundler Censorship Vector
Bundlers act as centralized gatekeepers. They can censor, reorder, or extract value from UserOperations by manipulating bundle construction, creating a trusted intermediary problem.
- Centralized Point of Failure: Users must trust a bundler's honesty and liveness.
- Value Extraction: Bundlers can insert their own profitable transactions into user bundles.
- Staking Centralization: Top bundlers like Stackup and Alchemy dominate, risking network resilience.
>70%
Top 3 Bundler Share
1
Trusted Party
03
Paymaster Trust & Solvency Risk
Paymasters sponsor gas fees, but their solvency and logic are critical. A malicious or bankrupt paymaster can cause widespread transaction failure or fund loss.
- Smart Contract Risk: Paymaster validation logic bugs can be exploited to drain sponsor funds.
- Systemic Failure: A major paymaster (e.g., Biconomy) going offline bricks dependent accounts.
- Economic Attack: Attackers can spam transactions to drain a paymaster's gas stipend, causing a denial-of-service.
$0
User Gas Cost
100%
Sponsor Risk
WHY ERC-4337'S USEROPERATION IS A HONEYPOT
EOA vs. Smart Account: Mempool Exposure Comparison
A first-principles breakdown of how transaction visibility and execution logic differ, creating distinct MEV and security attack surfaces for EOAs and ERC-4337 smart accounts.
| Attack Vector / Feature | Traditional EOA (e.g., MetaMask) | ERC-4337 Smart Account (via Bundler) | Implication for Attackers |
|---|---|---|---|
Transaction Data in Public Mempool | EOA tx is fully visible; UserOperation is not a standard tx. | ||
Pre-Execution Logic Visibility | None | Full | Bundler's mempool reveals full intent pre-validation. |
Atomic Front-Running Surface | High (e.g., DEX swap) | Theoretical (requires bundler collusion) | EOA tx is a single, executable unit. UserOperation requires bundler inclusion. |
Time-in-Mempool for Snipping | Seconds to minutes | Up to bundler's | Longer exposure window for analyzing profitable intents. |
Sender Identity Obfuscation | EOA address only | Can hide behind factory/paymaster until execution | Harder to link operations to final contract account pre-execution. |
Fee Payment Method | Native gas (ETH, MATIC, etc.) | ERC-20 via Paymaster (e.g., USDC) or sponsored | Paymaster logic reveals token approvals and sponsorship patterns. |
Required for Execution | Valid ECDSA sig | Passes account-specific | Signature is just one validation step; replay attacks are confined to the account. |
Primary MEV Extraction Method | Gas auction & transaction ordering | Bundle auction & operation ordering within a bundle | Shifts MEV from searcher->validator to searcher->bundler. See |
deep-dive
THE ATTACK SURFACE
The UserOperation Mempool is a Public Honeypot
ERC-4337's UserOperation mempool exposes pending transactions to predictable, extractable MEV.
UserOperations are public by design. Unlike private transaction pools used by searchers on Ethereum, the ERC-4337 mempool broadcasts pending UserOperations to all bundlers. This creates a predictable execution environment where attackers can front-run or sandwich any operation before a bundler includes it.
Paymasters are the primary attack vector. An attacker observes a UserOperation with a gas sponsorship promise from a paymaster like Biconomy or Stackup. They copy the operation, replace the beneficiary, and pay the gas themselves to steal the sponsored transaction's value.
Bundlers create centralized bottlenecks. To mitigate this, bundlers like Alchemy or Pimlico must run private mempools, which reintroduces centralization and trust that the ERC-4337 standard aimed to eliminate. The public alternative is a free-for-all for MEV bots.
Evidence: The Pimlico team documented a simulated attack where a malicious actor extracted over $20k in a day by exploiting predictable paymaster logic in a public mempool environment.
protocol-spotlight
SECURING THE INTENT SUPPLY CHAIN
Mitigation Strategies & Emerging Solutions
ERC-4337's UserOperation is a public, mempool-exposed intent that creates a new attack surface for frontrunning, denial-of-service, and censorship.
01
Private Mempools & SUAVE
Public mempools are the root vulnerability. Private order flow channels and shared sequencers like SUAVE encrypt intents off-chain.\n- Prevents frontrunning and sandwich attacks on user intents.\n- Enables cross-domain MEV extraction for the user, not against them.\n- Projects like Flashbots Protect and BloxRoute are early adopters.
~0s
Public Exposure
99%+
Attack Surface Reduced
02
Aggressive Bundler Rate-Limiting
The 'free for bundlers' UserOperation model invites spam. Implement strict economic and reputational checks before inclusion.\n- Stake-weighted prioritization penalizes malicious bundlers.\n- Paymaster pre-charging for gas upfront eliminates free DoS vectors.\n- Pimlico and Stackup enforce sender rate limits and whitelists.
10x
Higher Spam Cost
-90%
Junk Ops
03
Intent-Based Architecture (UniswapX, CowSwap)
Move computation off-chain. Don't expose a executable calldata UserOp; expose a declarative intent.\n- UniswapX and CowSwap solve this natively with off-chain solvers and on-chain settlement.\n- ERC-4337 can wrap these systems, using the account abstraction stack for sponsorship and security.\n- Across Protocol's optimistic bridge model is a canonical intent example.
Atomic
Execution
No Calldata
To Frontrun
04
The Stateless Client Future
Long-term, the mempool itself is the bug. Verkle trees and stateless clients allow validators to verify state proofs without storing global state.\n- Ethereum's roadmap aims to make the 1TB state obsolete.\n- Enables trustless propagation of UserOperations with attached proofs.\n- Near-instant finality for AA transactions, bypassing mempool risks entirely.
TB->KB
State Burden
~500ms
Theoretical Latency
05
Bundler Decentralization via ERC-4337 v0.7
A single, centralized bundler is a censorship point. ERC-4337's v0.7 introduces the EntryPoint v0.7 with Paymaster data segregation.\n- Enables permissionless bundler networks with slashing for malfeasance.\n- Separation of concerns between paymasters and bundlers reduces trusted roles.\n- EigenLayer AVS models could secure a decentralized bundler marketplace.
1 -> N
Bundler Model
0%
Single Point of Failure
06
Aggressive Paymaster Policy Enforcement
Paymasters are the economic gatekeepers. They must enforce strict policy engines on-chain before sponsoring ops.\n- Real-time risk scoring using oracles like Chainlink for gas price volatility.\n- Social recovery throttling to prevent wallet hijacking drains.\n- Gas tank models (like Biconomy) with hard limits per session or key.
<100ms
Policy Check
$10B+
TVL Protected
counter-argument
THE ARCHITECTURAL FLAW
The Rebuttal: "It's a Necessary Trade-off"
The UserOperation's public mempool is not a trade-off but a systemic vulnerability that invites front-running and denial-of-service attacks.
Public mempool exposure is the core vulnerability. The ERC-4337 standard requires UserOperations to be broadcast to a public, permissionless mempool before bundlers process them. This creates a honeypot for MEV bots and attackers who can observe, copy, and front-run any transaction.
Intent-based systems like UniswapX solve this by keeping user intent private until settlement. In contrast, ERC-4337's design leaks the full transaction details, including the target contract and calldata, enabling predictable exploitation.
The denial-of-service vector is severe. A malicious actor can spam the network with invalid UserOperations that bundlers must simulate, wasting computational resources and increasing costs for legitimate users, a flaw not present in private relay networks like those used by Blocto or Safe.
Evidence: The Pimlico team's analysis shows that without mitigations like private mempools or SUAVE-like encryption, over 90% of high-value UserOperations in a public mempool would be vulnerable to front-running.
takeaways
SECURITY ARCHITECTURE
Key Takeaways for Builders and Architects
ERC-4337's UserOperation is a novel primitive that, if misconfigured, creates systemic vulnerabilities across the account abstraction stack.
01
The Bundler as a Censorship & MEV Vector
Bundlers are the new miners. They see all pending UserOperations and can front-run, censor, or extract value. The mempool is public by default.
- Unencrypted Mempool: UserOps are visible, enabling generalized MEV extraction.
- Centralization Risk: Top bundlers (e.g., Stackup, Alchemy, Pimlico) control >70% of relayed volume, creating a single point of failure.
>70%
Bundler Concentration
~500ms
Front-Run Window
02
Paymaster Dependency is a Solvency Bomb
Paymasters sponsor gas, creating a critical credit system. If a paymaster runs out of funds or is malicious, user transactions fail or funds are stolen.
- Insolvency Risk: A popular paymaster draining its deposit can brick thousands of accounts.
- Trust Assumption: Users must trust the paymaster's logic not to rug or censor, reintroducing intermediaries.
$10M+
Typical Deposit
1
Single Point of Failure
03
Signature Aggregator Complexity Invites Bugs
ERC-4337 enables signature aggregation (e.g., BLS) for gas savings, but custom cryptographic verifiers are a new attack surface.
- Verifier Bugs: A flawed signature verifier in a smart account can lead to total fund loss.
- Audit Gap: Most teams lack crypto expertise to audit novel aggregation schemes, leading to vulnerabilities like those seen in zk-SNARK circuits.
-90%
Gas Savings (Potential)
High
Implementation Risk
04
The EntryPoint is a Universal Upgradeable Proxy
All UserOperations flow through a singleton EntryPoint contract. While it's immutable, its referenced logic (like Aggregators) can be upgraded, creating systemic risk.
- Upgrade Governance: A malicious or coerced upgrade could compromise all ERC-4337 accounts.
- Protocol Capture: Entities controlling the upgrade keys (like Ethereum Foundation) become high-value targets for state-level attacks.
1
Singleton Contract
All
Accounts Affected
05
Mempool Simulation is a DoS Attack Surface
Bundlers must simulate UserOps locally to check validity and paymaster sponsorship. This opens a vector for resource exhaustion attacks.
- Unbounded Computation: A malicious UserOp can force a bundler to simulate complex, gas-guzzling logic, crippling its node.
- Free Options: Attackers can spam simulation requests to probe paymaster/account logic at zero cost.
0
Simulation Cost
High
Node Load
06
Solution Pattern: SUAVE-Like Private Mempools
The fix is encrypted mempools and commit-reveal schemes, moving towards architectures like Flashbots' SUAVE or CowSwap's batch auctions.
- Encrypted Intent Flow: User intents are encrypted until execution, preventing front-running.
- Decentralized Bundling: A network of competing searchers/bundlers reduces centralization, similar to UniswapX and Across.
~0
Visible MEV
Multi-Chain
Future Scope
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Confidentiality24h Response
Time to ValueDirectly to Engineering Team
No Sales Fluff10+
Protocols Shipped
$20M+
TVL Overall