Insufficient Balance on-chain error EIP

insufficient-balance-eip.md

Currently, a signed transaction that sends more ether than an account has is considered an invalid transaction, and is not mined.

This can cause a dangerous situation where a user sends funds they didn't mean to, and can be completely avoided by allowing miners to process "insufficient balance" as an on-chain error.

Reproduction steps:

• A user with balance X signs and broadcasts TX A for a max possible value Y (value + gasPrice * gasLimit) where Y < X.
• Before that tx is mined, the user impatiently signs and broadcasts TX B, with an incremented nonce, for max possible value Z where Z < X && Z + Y > X.
• Because each of these transactions are less than the user's current balance, they are both added to miner mempools.
• Transaction A is valid, and is mined.
• Transaction B has undefined behavior. Some nodes may forget it, but it may be passed among peers and remembered at any time.
• The user forgets about the whole thing, doesn't think about the 2nd "retry" transaction.
• The user sends ether to account X, funding its balance so that its new balance Q > Z.
• A miner processes transaction B.
• The user is shocked to find their ether was "spontaneously" sent away.

Fix idea:

• If a miner receives a Transaction from an account with balance X for max possible value Y where Y > X, miners should be able to process that transaction on-chain, spending its gas, to prevent the transaction from being accidentally valid in the future.