ACryptoS depositMulti Vault Share-Minting Exploit

On November 8, 2026, ACryptoS, a multi-chain DeFi yield aggregator, was drained of approximately $665,000 when an attacker exploited a missing input check in its vault deposit logic, looting 77 of 126 vaults across five networks.

What happened

The flaw sat in depositMulti(uint256[] amounts, uint256 minShares), which never verified that the amounts array length matched the vault's token count. Passing a one-element array to a two-token concentrated-liquidity vault made it price the deposit using only token0 while ignoring token1 holdings, so a tiny deposit minted the bulk of a vault's shares. withdrawMulti then redeemed those shares against both underlying assets, extracting the mispricing. On a Polygon fork, a 10 USDC deposit with a one-element array minted 66.84% of the share supply, versus about 0.01% for a correctly sized array. The campaign ran from 02:02 to 16:22 UTC across Arbitrum ($230K), BNB Chain ($191K), Polygon ($135K), Base ($70K) and Optimism (~$40K); Linea vaults were untouched. Investigators at SlowMist counted 135 attacker addresses and roughly 1,000 exploit deposits.

Aftermath

ACryptoS disabled deposits on all vaults by 16:40 UTC — closing the first chain within 80 minutes of reaching the developer and all chains within about 2.5 hours via per-vault beacon upgrades — while leaving withdrawals open. The team said it would deprecate the protocol with no relaunch planned, urging users to withdraw remaining funds. Most proceeds were swapped into ETH, WETH or WBNB and bridged out, leaving under $1,000 in freezable stablecoins; the project burned one exploiter's shares in a Base vault to preserve about $6,187 USDbC for depositors. A reported 10% white-hat bounty could not be confirmed in the project's own statements, and no funds had been returned.

Why it matters

ACryptoS is a textbook share-accounting bug: like classic ERC-4626 first-deposit and inflation attacks, it turned a vault's own share-minting math into a drain, with no price oracle or flash loan required. The one-line omission — never checking array length against token count — mirrors how small input-validation gaps keep producing outsized losses in DeFi, echoing other recent smart-contract failures like TENDRIL and UNCX Network. It also underscores that breadth, not depth, defines multi-chain risk: a single shared contract flaw let one bug cascade across five networks and 77 vaults at once, and an unfunded, volunteer-maintained protocol had little choice but to wind down rather than make users whole.