Infinite approval

The ERC-20 standard separates the approve, which sets how much a contract may spend, from the transferFrom, which executes the movement. Approving the maximum amount, the value 2 to the power of 256 minus 1, avoids having to re-approve on every interaction, saving gas and friction, but leaves a permanently open key. The risk appears if the spender contract has a bug, is maliciously upgraded through a proxy, or was a drainer from the start: it can empty the entire balance of that token at any time.

Why it matters for security hygiene. An infinite approval forgotten years ago toward a protocol that is later compromised is a latent attack surface; it is the amplification that turns a single-click phishing into a total drain of the token, and it is often granted under blind signing. The mitigations are approving the exact amount needed, using Uniswap's Permit2 model, deployed in November 2022, which adds expiration and limits to signatures, and reviewing and revoking allowances with Revoke.cash or the Etherscan panel.

A related standard is ERC-2612, which enables gasless off-chain signature approval and is natively implemented by tokens like USDC and DAI. Permit2 is the reference example of redesigning the allowance model to contain this problem. Reviewing approvals periodically is the simplest and most effective practice.