The September 2024 wave of cryptocurrency exploits — including the $44 million BingX breach, the $27 million Penpie reentrancy attack, and the growing epidemic of permit phishing scams — has exposed a critical vulnerability that most users overlook: unmanaged token approvals. Every time you interact with a decentralized application, you grant smart contract permissions that can persist indefinitely. This advanced tutorial walks through the technical process of auditing, understanding, and revoking these permissions to secure your wallet against exploitation.
The Objective
Token approvals are a fundamental mechanism in Ethereum and EVM-compatible blockchain applications. When you swap tokens on a decentralized exchange, provide liquidity to a lending protocol, or stake assets in a yield farm, you are granting a smart contract permission to spend tokens on your behalf. These approvals specify which contract can move which tokens, and in what quantities. The problem is that most users accumulate dozens or hundreds of active approvals across multiple chains without ever reviewing or revoking them.
The September 2024 permit phishing attacks exploit this exact oversight. Attackers create convincing interfaces that prompt users to sign approval transactions disguised as routine operations — verification, claiming rewards, or connecting to a new protocol. Once signed, the attacker gains a spending allowance on the user tokens, which can be exercised at any time, often draining wallets completely.
The objective of this tutorial is to give you complete visibility into your active token approvals across all EVM-compatible chains and the ability to revoke any that are unnecessary or suspicious. By the end, you will have a clean, audited approval state and a repeatable process for maintaining it.
Prerequisites
Before beginning, ensure you have access to your wallet through a web3 interface — MetaMask, Rabby, or any wallet that supports custom network interactions. You will need a small amount of native tokens on each chain where you plan to revoke approvals, as revocation transactions require gas fees. For Ethereum mainnet, this means ETH. For BNB Chain, BNB. For Polygon, POL. For Arbitrum, ETH. Plan for approximately $2 to $5 per chain in gas costs for a typical cleanup operation.
You should also have a basic understanding of how ERC-20 token approvals work at the contract level. When you call the approve function on an ERC-20 token contract, you set an allowance for a spender address. The allowance represents the maximum number of tokens the spender can transfer from your balance. An unlimited approval — commonly set to the maximum uint256 value — gives the spender unrestricted access to your entire balance of that token, now and in the future, until you explicitly revoke it.
Finally, ensure you are using a secure, uncompromised device. If you suspect your computer may be infected with malware, perform this process from a clean environment. The entire point of this exercise is to secure your assets, and conducting it on a compromised machine would be counterproductive.
Step-by-Step Walkthrough
Step 1: Inventory Your Wallet Addresses — Compile a complete list of all wallet addresses you actively use across all EVM-compatible chains. This includes your primary MetaMask account, any hardware wallet-connected addresses, and any secondary accounts. You will need to check each address individually.
Step 2: Use Approval Tracking Tools — Navigate to an on-chain approval tracking tool. Several reliable options exist, including Etherscan Token Approval Checker for Ethereum mainnet, and multi-chain tools like Revoke.cash and Rabby Wallet built-in approval scanner. These tools connect to your wallet and display all active token approvals in a readable format, showing the token contract, the spender contract, and the remaining allowance.
Step 3: Analyze Each Approval — For each active approval, ask three questions. First, do I recognize the spender contract? If not, it may be a phishing contract or an abandoned protocol. Second, do I still actively use this protocol? If you stopped using a DEX or lending platform months ago, its approval is an unnecessary risk. Third, is the approval amount unlimited? Unlimited approvals are convenient but dangerous — if the protocol is compromised, the attacker can drain your entire balance of that token.
Step 4: Revoke Unnecessary Approvals — For each approval you want to remove, use the revoke function within the tracking tool or manually call the token contract approve function with the spender address and an amount of zero. This immediately sets the spending allowance to zero, preventing the spender from transferring any of your tokens. Confirm the transaction in your wallet and wait for it to be included in a block.
Step 5: Set Limited Approvals Going Forward — When interacting with new protocols, use exact-amount approvals rather than unlimited ones wherever possible. Some interfaces offer this option — if swapping 1,000 USDC, approve exactly 1,000 USDC rather than the unlimited default. While this requires more frequent approval transactions, it limits exposure to the specific amount you intend to use. Modern DEX interfaces increasingly support permit2 signatures that offer more granular and time-limited permissions as an alternative to traditional unlimited approvals.
Troubleshooting
If a revocation transaction fails, the most common cause is insufficient gas. Ensure you have enough native tokens to cover the transaction fee. On congested networks like Ethereum mainnet, gas prices can spike significantly — use a gas tracker to time your transactions for lower-fee periods, typically during off-peak hours.
If you discover approvals to contracts you do not recognize and suspect may be malicious, prioritize revoking those immediately. Do not interact with the suspicious contract in any way — simply revoke the approval and move on. If funds have already been moved by a suspicious contract, contact the relevant blockchain security firms and document all transaction hashes for potential investigation.
For multi-chain wallets, remember to switch your wallet network to the correct chain before attempting to view or revoke approvals. Approval tracking tools typically show approvals only for the currently connected network. If you use Arbitrum, Optimism, Base, Polygon, BNB Chain, and Ethereum, you need to check each chain separately.
Mastering the Skill
Token approval management should become a regular practice, not a one-time exercise. Schedule a monthly approval audit where you review and clean up permissions across all your active chains. Each audit takes approximately 15 to 30 minutes and can prevent catastrophic losses. Consider using a wallet like Rabby that provides built-in approval warnings and automatic revocation suggestions, streamlining the process significantly. The $120 million lost in September 2024 crypto hacks affected victims who, in many cases, could have been protected by better approval hygiene. In a ecosystem where smart contract permissions are the keys to your digital assets, managing those permissions with the same diligence you apply to your private keys is not optional — it is essential.
Disclaimer: This article is for informational purposes only and does not constitute financial or investment advice. Always conduct your own research before making investment decisions.
this is the kind of guide everyone in crypto needs to read but nobody does until they get drained. permit phishing is responsible for way more losses than most people think
bingx lost $44M and penpie $27M in the same month and both could have been mitigated with better approval hygiene. the tools exist, people just don’t use them
bingx $44M and penpie $27M in the same month and both were preventable with basic approval hygiene. the tools exist
I audited my own approvals after reading this and found 47 active ones I had totally forgotten about. some were unlimited spend approvals from defi farms I stopped using months ago
^ 47 is actually low. seen people with 200+. revoke.cash is your friend people
47 is rookie numbers lol. checked mine after the penpie exploit and had 89 active across 4 chains
unlimited spend approvals are the real killer. you approve 1000 tokens for a one-time swap of 50 and the contract can drain the rest whenever
unlimited approvals should be opt-in not default. the fact that most DEX UIs still default to infinite is negligent