Notional Finance (V1 escrow) hack — September 2026

An abandoned Notional Finance escrow contract was emptied of about $1.73m in the small hours of 4 September 2026. The setup transaction landed at 23:58:47 UTC on 3 September in block 25,900,220 and the drain confirmed two minutes and forty-eight seconds later, at 00:01:35 UTC, in block 25,900,234. The contract gave up 69,257.38 DAI and 1,658,524.86 USDC.

The bug is arithmetic. The attacker called mintfCashPair() twice to build a future-cash liability of negative two to the power 128. The free-collateral valuation then cast that number down to a uint128 without checking whether it fit, and the excess digits were simply discarded, leaving a debt that evaluated to zero. An account with no debt may withdraw everything, and it did. CertiK's reading is that an explicit overflow check would have reverted the transaction rather than silently dropping the digits.

The proceeds were converted to 689.2 ETH and pushed through Tornado Cash in a sequence of transfers between 00:15:59 and 00:30:11 UTC, inside half an hour of the drain.

What makes this worth recording is not the size. The contract at 0x9abd...f683 is a legacy deployment: mintfCashPair() belongs to Notional's first version, and Notional had already wound the protocol down elsewhere. On 3 November 2025 the Balancer V2 exploit hit five leveraged vaults across Ethereum and Arbitrum, reducing their collateral to zero and leaving 632.8 ETH of bad debt on mainnet and 80.2 ETH on Arbitrum. Notional concluded it could not return V3 to a working state, wound it down, migrated cross-currency borrowers to Aave and distributed what remained, with mainnet ETH lenders taking a 56.019% haircut on their ETH asset value. The V1 contracts were never part of any of that. They stayed deployed and funded, and nobody swept them. This is the second such case in five days: the Balancer V1 rounding bug of 31 August, recorded elsewhere in this registry, drained another unmaintained deployment whose company no longer exists.

The figure should be read as preliminary. Specter's monitoring flagged the transactions and PeckShield issued its alert using the word may; Notional has published no incident report and confirmed no loss. The DefiLlama dataset lists this entry under the name Notional V2, but the exploited function and the contract's own labelling are V1's.