Infinite Approval

An infinite approval grants a smart contract the permission to spend an unlimited amount of a specific token from the user's wallet. Unlike a standard approval with a defined limit (e.g., 100 USDC), this authorization has no upper bound, allowing the contract to transfer the user's entire current and future balance of that token.

• Key Mechanism: The approval amount is set to the maximum possible value for the uint256 data type: 2^256 - 1.
• Purpose: Designed for convenience in protocols like DEX aggregators or lending platforms where users frequently interact.

The primary risk of an infinite approval is that it creates a persistent vulnerability. If the approved smart contract is later compromised due to a bug or exploit, or if it is malicious from the start, the attacker can drain all tokens of that type from the user's wallet.

• Attack Vector: A single compromised contract can lead to catastrophic, one-step fund loss.
• Persistence: The approval remains active until explicitly revoked by the user, posing a long-term threat.

Infinite approvals are often requested by Decentralized Exchanges (DEXs) and aggregators (like 1inch or Matcha) to facilitate multi-step swaps without requiring intermediate approvals. They are also common in lending protocols (like Aave or Compound) where users may frequently deposit and withdraw collateral.

• Developer Convenience: Simplifies the user experience by reducing transaction friction.
• Gas Optimization: Avoids the gas cost of submitting a new approval transaction for every interaction.

To manage risk, users and developers should adopt specific practices:

• Use Allowance Checks: Wallets and interfaces should warn users when an infinite approval is requested.
• Prefer Limited Approvals: Grant only the exact amount needed for a transaction or a reasonable limit for repeated use.
• Regularly Revoke Approvals: Use tools like Etherscan's Token Approval Checker or Revoke.cash to review and revoke unused permissions.
• Contract Security: Interact only with well-audited, reputable protocols.

Infinite approval is enabled by the standard ERC-20 approve() function. This function updates the allowance mapping, which tracks how much a spender (a contract) can withdraw from the owner's balance.

• Function Signature: approve(address spender, uint256 amount)
• State Variable: The allowance[owner][spender] is set to the provided amount.
• Maximum Value: Setting amount to type(uint256).max or 2**256 - 1 creates the infinite approval state.

EIP-2612 permit() is a gas-efficient alternative to approve() that uses off-chain signatures. A user signs a message granting an allowance, which can then be submitted by a relayer. While also capable of granting infinite approvals, its key innovation is enabling approvals without a prior on-chain transaction.

• Gas Savings: Eliminates the need for a separate approve transaction.
• Same Risks: The permit message can also authorize an infinite amount, carrying identical security implications if misused.

An infinite approval (or unlimited approval) is a token allowance set to the maximum possible value (e.g., 2^256 - 1). This grants a smart contract the ability to transfer an unlimited quantity of a specific token from the user's wallet at any time. While convenient for repeated interactions, it creates a persistent attack vector: if the approved contract is later exploited or contains malicious code, the attacker can drain the entire approved token balance from the user's wallet.

The primary risk materializes when a previously trusted protocol is compromised. Common attack vectors include:

• Contract Exploits: A bug or vulnerability in the approved contract allows an attacker to call the transfer function.
• Admin Key Compromise: If the contract owner's private keys are stolen, the attacker can upgrade the contract to a malicious version.
• Phishing & Fake Contracts: Users mistakenly approve malicious contracts disguised as legitimate dApps.

Historical incidents, like the Uniswap and SushiSwap LP token approvals exploited in 2020, demonstrate how infinite approvals in old, unused contracts led to significant user losses long after initial interaction.

Users should adopt a principle of least privilege for token approvals:

• Use Limited Approvals: Always specify the exact amount needed for a transaction. Most modern wallets (MetaMask, Rabby) now warn against or default to limited approvals.
• Revoke Unused Approvals: Regularly review and revoke old approvals using tools like Etherscan's Token Approval Checker, Revoke.cash, or built-in wallet features.
• Verify Contracts: Double-check the contract address you are approving and be wary of signatures requesting unlimited spending.

The ERC-20 standard enabled infinite approvals via the approve function. Newer standards and patterns aim to reduce risk:

• ERC-2612 (Permit): Allows token approvals via off-chain signatures, enabling single-transaction interactions without a prior approval transaction, reducing exposure windows.
• IncreaseAllowance/DecreaseAllowance: Safer functions that prevent front-running attacks associated with the standard approve.
• dApp Design: Protocols can implement periodic re-authorization prompts or use meta-transactions to avoid persistent allowances altogether.

Wallet providers and blockchain analytics platforms have built tools to combat approval risks:

• Approval Warnings: Wallets like MetaMask display prominent warnings for infinite approval requests.
• Approval Managers: Dedicated dashboards (e.g., within Rabby Wallet) let users view, limit, and revoke all approvals in one interface.
• Simulation & Security Services: Platforms like Tenderly and OpenZeppelin Defender can simulate transactions to detect unexpected approval calls, while Chainscore monitors for abnormal allowance patterns as a risk signal.

Understanding infinite approval requires context on related mechanisms:

• Allowance: An ERC-20 mechanism where a token owner (owner) authorizes a third-party spender contract to transfer tokens on their behalf, up to a specified limit.
• Gasless Transactions (Meta-Transactions): A pattern where a relayer pays the gas fee for a user's transaction. Often relies on ERC-2612 permits or similar signing schemes, which can eliminate the need for a prior on-chain approval transaction, thereby reducing the attack surface compared to a standing infinite approval.

An infinite approval is a token allowance where a user authorizes a smart contract to spend an unlimited amount of their tokens. This creates a persistent risk: if the approved contract is later exploited or contains malicious code, the attacker can drain the user's entire token balance for that asset. Unlike a limited allowance, this risk remains until the user manually revokes it.

The primary user-level defense is to grant only the exact allowance needed for a transaction. Modern wallets like MetaMask often suggest this by default. Best practices include:

• Approving only the amount required for the immediate swap or interaction.
• Using periodic, small approvals for recurring actions (e.g., weekly DCA).
• This limits potential loss to the approved amount, not the entire wallet balance.

Advanced standards eliminate the need for on-chain approvals altogether. ERC-2612 (Permit) allows users to sign off-chain messages to grant token permissions, which are submitted in the same transaction as the action. Permit2, a canonical smart contract, builds on this by enabling secure, revocable, and cross-app token approvals, significantly reducing phishing and stale approval risks across the ecosystem.

Wallet providers play a crucial role in risk mitigation through user experience:

• Defaulting to limited approvals and displaying the exact amount.
• Clear warnings when a user attempts to grant an infinite approval.
• Integrated approval managers within the wallet interface for easy review and revocation.
• Educating users on the difference between approve and increaseAllowance calls.

The ecosystem is shifting towards eliminating infinite approvals as a default. Key initiatives include:

• Auditors flagging unnecessary infinite approvals as medium-severity issues.
• Major DEXs and protocols migrating to Permit2 or implementing max-only approvals.
• Educational campaigns by security firms to raise user awareness. The goal is to make limited, intent-driven approvals the standard, reducing the overall attack surface.

A delegate call is a low-level EVM opcode that allows a contract to execute code from another contract while preserving the original contract's storage context. It is a common attack vector exploited to drain funds from contracts with infinite approvals.

• Mechanism: A malicious contract uses delegatecall to make the user's wallet contract call transferFrom on itself.
• Famous Exploit: Used in the Parity Wallet hack.
• Connection to Infinite Approval: Wallets or contracts holding infinite approvals are high-value targets for delegate call attacks.

Gas fee optimization is the primary user incentive for granting infinite approvals. By approving once for an unlimited amount, users avoid paying gas fees for repeated approve transactions when interacting with the same dApp.

• Trade-off: Convenience and cost savings vs. persistent security risk.
• Common Pattern: Used heavily by DEX aggregators and yield farming protocols where users make frequent trades or deposits.
• Alternative: Setting a large, finite allowance (e.g., 10,000 tokens) can provide similar convenience with capped risk.

A wallet drainer is a type of malicious smart contract or script designed to steal all approved assets from a victim's wallet. Infinite approvals are the primary enabler for these attacks.

• Attack Flow: 1) User signs a malicious transaction. 2) Drainer contract calls transferFrom for each approved token. 3) Funds are sent to the attacker's address.
• Social Engineering: Often distributed via phishing websites, fake airdrops, or compromised Discord announcements.
• Prevention: Revoking unused approvals and verifying all transaction requests are the best defenses.