Step-by-Step Guide: How to Revoke Smart Contract Approvals After the Curve Finance Exploit

On July 24, 2023, the DeFi community woke up to alarming news: Curve Finance, one of the most trusted decentralized exchanges in the ecosystem, had been exploited for approximately $52 million due to a re-entrancy vulnerability in certain Vyper compiler versions. Multiple stablecoin pools were drained, and several other protocols built on top of Curve were also affected. If you have ever interacted with Curve Finance, Alchemix, JPEG’d, Metronome, or any Vyper-based smart contract, this guide walks you through exactly what to do right now to protect your funds.

Understanding the Vulnerability

The exploit targeted a specific vulnerability in the Vyper programming language compiler, versions 0.2.15, 0.2.16, and 0.3.0. These versions failed to properly implement re-entrancy guards, a fundamental security feature that prevents malicious contracts from repeatedly calling back into a vulnerable function before the first call completes.

Re-entrancy attacks work like a bank that allows you to withdraw money, then before updating your balance, the attacker calls the withdraw function again and again until the vault is empty. In this case, attackers exploited Curve pools that used the affected Vyper versions, draining liquidity from multiple stablecoin pairs including CRV/ETH, alETH/ETH, and msETH/ETH.

It is important to understand that this was not a flaw in Curve’s design or code logic. The vulnerability existed in the compiler itself, meaning the Curve team’s code was written correctly but was compiled into vulnerable bytecode by the Vyper toolchain. This distinction matters because it means other protocols using the same Vyper versions could also be at risk.

Step 1: Check Your Exposure

Before taking any action, determine whether your wallets have interacted with the affected contracts. Visit the Curve Finance exploit tracker or use a blockchain explorer like Etherscan to review your recent transactions.

Enter your wallet address on Etherscan and check your transaction history for any interactions with the following contracts: Curve pools using Vyper 0.2.15-0.3.0, Alchemix alETH pools, JPEG’d pETH-ETH pool, and Metronome msETH pools. If you find interactions with any of these contracts, proceed to the next steps immediately.

Even if you do not currently hold funds in these pools, previous approvals you granted may still be active, meaning a malicious actor could potentially drain your tokens if the compromised contract is exploited further.

Step 2: Revoke Token Approvals

Token approvals are permissions you grant to smart contracts to spend tokens on your behalf. After interacting with DeFi protocols, these approvals often remain active indefinitely. Revoking them is your most important defensive action.

Navigate to Revoke.cash or a similar approval management tool. Connect the wallet you used to interact with Curve or affected protocols. The tool will display all active spending approvals associated with your address. Look specifically for approvals related to Curve, Alchemix, JPEG’d, Metronome, and any Vyper-based contracts.

For each approval related to the affected contracts, click the revoke button. You will need to confirm the transaction in your wallet and pay a small gas fee. Ethereum gas prices at the time of writing hover around 15-25 gwei, so each revocation should cost roughly $1-3 depending on network congestion.

Revoking an approval does not affect your ability to use the protocol in the future. You simply need to re-approve the next time you want to deposit or interact with the contract, at which point the patched versions should be in place.

Step 3: Withdraw From Affected Pools

If you currently have liquidity deposited in any Curve pool or related protocol, assess whether the pool has been patched. Curve and the affected protocols have been working around the clock to patch vulnerable contracts, but some pools may still be at risk.

Visit the official Curve Finance interface at curve.fi to check the status of each pool. Pools that have been patched will display normally, while vulnerable or drained pools may show warnings or reduced liquidity. If a pool you are invested in has not been explicitly confirmed as safe, withdraw your funds as a precaution.

For Alchemix users, check the official Alchemix communications on their Discord and Twitter channels for specific instructions regarding the alETH pool. JPEG’d users should monitor the project’s official channels for updates on the pETH-ETH pool status.

Step 4: Verify Your Wallet Safety

After revoking approvals and withdrawing from affected pools, take additional steps to verify your overall wallet security. Check your token balances for any unexpected changes or unauthorized transfers. Review your wallet’s connected dApps and remove any connections you no longer need.

If you notice any unauthorized transactions, document everything immediately. Take screenshots of the transaction hashes, timestamps, and amounts. Report the incident to the relevant protocol teams and consider posting in community forums to warn other users.

For users with significant holdings, consider moving your assets to a fresh wallet address that has never interacted with any DeFi protocol. This eliminates any risk from lingering approvals or unknown vulnerabilities in contracts you may have touched months or years ago.

Preventative Measures for the Future

This exploit offers several lessons for safer DeFi participation. First, make approval revocation a regular habit. Set a calendar reminder to review and revoke unused approvals monthly. Tools like Revoke.cash, Unrekt, and Rabby Wallet all provide approval management features.

Second, use a hardware wallet for all significant DeFi interactions. Hardware wallets require physical confirmation for every transaction, including token approvals. This extra step forces you to review each approval consciously rather than blindly clicking through MetaMask prompts.

Third, diversify your protocol exposure. Concentrating all your liquidity in a single protocol or pool increases your risk when vulnerabilities are discovered. Spreading funds across multiple reputable, independently audited protocols reduces the impact of any single exploit.

Summary

The Curve Finance exploit of July 2023 was a wake-up call for the entire DeFi ecosystem. Even well-audited, blue-chip protocols can be vulnerable when their underlying tools contain flaws. By following the steps in this guide — checking your exposure, revoking approvals, withdrawing from affected pools, and adopting preventative habits — you can protect your assets and participate more safely in decentralized finance going forward.

Disclaimer: This guide is for educational purposes only and does not constitute financial or security advice. Always verify information through official protocol channels before taking action.