Three checks to reduce allowance races in bridge wallets
Three checks—spender, amount and transaction order—help bridge users limit token approvals and avoid replacing a live allowance before it is spent on the source chain.
3 min read
Bridge-wallet users can reduce allowance races by checking the spender, limiting the amount and confirming each approval before replacing it. An ERC-20 allowance lets a named contract spend tokens from a wallet; changing a non-zero allowance can leave the old amount spendable until the update is confirmed. If the spender uses the old allowance before the update and then uses the new one, both amounts may be spent.
Which contract is the wallet asking you to approve?
Check the token, source network and spender address in the approval prompt before signing. A bridge transaction can involve a token contract, a bridge contract and other route components, but the allowance should name the contract that needs permission to transfer the token. The destination address is not a substitute for checking the spender.
If the route is unfamiliar, read how AcrossBridge handles first transfers for a walkthrough of the bridge flow. Keep that route explanation separate from the approval check: the wallet prompt shows which contract will receive permission.
How much token allowance should you grant?
Approve only the amount the transfer needs when the wallet and token support a precise allowance. An unlimited approval can make later transfers easier, but it leaves the spender able to use the approved balance until that permission is reduced or revoked. That convenience is a poor trade for a one-off bridge transfer.
- Match the token and source chain to the intended transfer.
- Prefer the transfer amount over an unlimited allowance.
- Review any existing allowance before adding more permission.
Some tokens or interfaces handle approvals differently, so follow the transaction details the wallet displays rather than assuming every token uses the same flow.
How do you change an existing allowance safely?
Do not submit a new non-zero amount while a previous approval change is still pending. If you need to replace an existing allowance, set it to zero first when the token supports that method, wait for confirmation, then approve the required amount. This separates the old permission from the new one and reduces the window in which both could be used.
Before signing, check that each transaction is on the source chain and that the amount and spender match the route. After the bridge transfer, review whether the allowance remains; revoke it if you no longer need that spender to move tokens. For most occasional users, a limited approval and a confirmed transaction sequence are the clearest way to keep permission tied to one transfer.