Token Approvals: They Stay Active Until You Revoke Them

Crypto authorizations granted to a contract remain active as long as you don’t withdraw them. From May 5, 2026, attackers exploited this rule. They withdrew approximately 1.42 million dollars from 31 addresses, thanks to authorizations given to a router of the Ekubo protocol. The main victim had granted theirs 158 days earlier, according to the founder of SlowMist.

A crypto authorization does not stop with the transaction

To exchange a token on a decentralized application, you first sign an authorization. This message thus allows a contract to withdraw your tokens on your behalf. The ERC-20 standard stipulates that it can do so “multiple times, up to the set amount”. However, your wallet does not always display what you are signing, as shown in our article on clear signing.

Moreover, this authorization has no end date. The official ethereum.org guide on revocation states plainly: “There is no expiration date on contract permissions.” They can therefore be used years later.

Disconnecting from the site does not change anything either. The authorization exists in the token’s contract, on the blockchain, and not in your browser. According to the same guide, the project therefore retains access to your tokens after disconnection. Your digital wallet does indeed keep your keys, not your authorizations. You must then revoke the authorization to cut this access.

The amount then poses a second problem. Many applications request unlimited access, so as not to ask again at each exchange. A university study published in 2022 measured this on transactions made up to July 31, 2021. At the time, 60% of authorizations on Ethereum were for an unlimited amount.

Crypto authorizations: what you think you accept

When you validate an exchange, you think you authorize only that single operation. In reality, the authorization goes further. It allows the contract to take a token amount, at any time, until withdrawn.

As long as the contract functions well, it only withdraws for your own operations. However, a code flaw can allow a third party to trigger the withdrawal. The authorization does not verify who calls the contract. It only checks that the contract has the right to take your tokens.

Ekubo has revised its own explanation. On May 8, its report probably attributed large authorizations to users who raised the ceiling themselves. On May 16, the text changed. The team indicates that its interface may have created some of these authorizations and no longer tries to attribute their origin.

Ekubo: how a forgotten router drained wallets

Ekubo is an exchange protocol present on Starknet and on several blockchains compatible with Ethereum. The attack targeted the HuffRouter, a router optimized to reduce fees, deployed on Ethereum and Arbitrum. Its users had indeed given it the right to withdraw their tokens to execute their exchanges.

A data parsing bug in HuffRouter […] allowed a caller to add arbitrary bytes after a otherwise valid exchange path, and have them interpreted as data set by the router upon settlement.

Ekubo, incident report

Specifically, the attacker could designate any user as the payer of an exchange. Anyone who had authorized this router thus became a target. The first withdrawal was on May 5, 2026, at 5:50 p.m. UTC.

Ekubo estimates losses at around 1.42 million dollars, across 31 addresses. However, a single address lost about 17 WBTC, or nearly 1.37 million dollars, as well as 0.34 cbBTC. It therefore concentrates 98% of the total. The attack did not affect the liquidity providers nor the Starknet version of the protocol.

The team also acknowledges not having audited this contract. They considered its risk low. According to them, authorizations could be limited, and exchanges via the interface should remain small and rare. These routers can no longer be modified: they “remain vulnerable,” the report specifies. Ekubo then deployed on June 23 a reimbursement fund, capped per address and voluntarily paid by its DAO.

Socket, LI.FI, SwapNet: the same pattern for years

Ekubo is not an isolated case. The site Revoke.cash lists these attacks in its annual report. It counts 9 authorization exploits in 2025, totaling just over 6 million dollars. In 2024, they had cost 80 million.

In July 2024, the LI.FI platform lost about 11.6 million dollars, taken from 153 wallets. According to the report published by LI.FI, the flaw only affected unlimited authorizations. In January 2024, a similar flaw at Socket targeted about 200 users, all with unlimited access.

In January 2026, 18 users lost 13.43 million dollars through SwapNet’s contracts. According to the post-mortem of the Matcha Meta platform, victims had disabled the one-time use authorization offered by default. Matcha notes, however, that a precise unused amount also left funds exposed.

These attacks differ from signature scams. In that case, a fake site makes you sign an authorization for the scammer. This type of theft cost 83.85 million dollars in 2025, according to the 2025 report from security company ScamSniffer.

Reducing the risk of crypto authorizations

The first reflex is to limit the amount. MetaMask allows setting a spending cap when signing. Their official help is clear: “Never grant unlimited (astronomically high) authorizations.”

Then, clean up regularly. The tool Revoke.cash displays your crypto authorizations on more than 80 networks. The verifier on the Etherscan explorer does the same on Ethereum. Revoking one authorization at a time is free, excluding network fees. Revoke.cash charges 1.50 dollars per batch revocation. In a January 2024 advisory, the police and cybersecurity agency of Singapore also recommend reviewing and revoking large authorizations.

Finally, some applications already limit the duration. The Uniswap application uses Permit2 and grants 30-day authorizations, according to its help center. However, you first give an authorization to the Permit2 contract itself, and that one does not expire. On Starknet, tokens follow the same model as Ethereum, without expiration.

ERC-8255 wants authorizations to expire by default

On May 6, 2026, Moody Salem, founder of Ekubo, submitted the project ERC-8255 on the EIP site. Its principle is simple: a classic authorization would expire after a maximum duration, set by each token. A new function would also allow granting a shorter authorization, down to a single block.

The text first adds new functions, compatible with existing applications. However, it changes the behavior of ordinary authorizations, which divides developers. On the Ethereum Magicians forum, some prefer to leave the classic authorization untouched. Researcher pcaversaccio believes instead that “authorizations have always been a bug, not a feature” (editorial translation).

Other approaches also exist. The ERC-7674 proposal provides for authorizations erased at the end of the transaction. Since the Pectra update of May 2025, a compatible wallet can also bundle authorization and exchange in a single operation.

As of October 18, 2026, ERC-8255 remained a project, and its text referenced no implementation. The Ekubo routers targeted on May 5 cannot be modified. Their unlimited authorizations therefore only disappear if each user revokes them. Our comparison of the most secure crypto wallets presents other available protections.