Push Payment

Push Payment Explained in Detail

Push payment sends ETH or tokens to a recipient during another operation. For example, an auction may try to refund the previous bidder inside the new bid() call.

This is simple, but it gives recipient code a chance to revert, consume gas, or reenter.

Smart contract example

(bool ok, ) = recipient.call{value: amount}("");
require(ok, "payment failed");

If recipient is untrusted, this can block the parent operation.

Push Payment in Auditing

Push payments are a common source of reentrancy and denial of service. One malicious recipient can sometimes freeze bidding, distribution, liquidation, or settlement.

Auditors ask whether a pull payment design would be safer.

Red flags in code

• Refunds are sent inline to untrusted addresses.

• Batch payouts require every recipient to accept payment.

• State updates happen after the payment call.

• Low-level call results are ignored.

• transfer or send is assumed to be universally safe.

How to test or review it

• Test recipients that revert, consume gas, and reenter.

• Check whether one failed payment blocks unrelated users.

• Review state ordering with checks-effects-interactions.

• Test batch payout limits.

• Consider converting risky refunds into pull payments.