$40M GMX Reentrancy Exploit Leads Week of Smart Contract Failures
GMX lost $40M after allowing contract calls in a critical redemption function. Hacken saw $250K minted from a compromised key. Bankroll dropped $65K due to a classic integer underflow in outdated Solidity. Three different failure classes, one shared root: unchecked access where trust assumptions break.
In Brief
GMX lost $40M after a smart contract reentrancy attack.
Hacken lost $250K due to a compromised minter wallet key used to mint unauthorized tokens.
Bankroll lost $65K after an integer underflow in its sell() function let an attacker manipulate payouts.
Hacks Analysis
GMX | Amount Lost: $40M
On November 4th, the GMX exploit on Arbitrum resulted in a $40M loss. The root cause was that the executeDecreaseOrder() function accepted a smart contract as an input instead of an externally owned account (EOA). Unlike EOAs, smart contracts can execute arbitrary logic during callbacks. This allowed the attacker to reenter and manipulate internal state mid-transaction. If the function had restricted access to EOAs only, the reentrancy attack would not have been possible. The attacker opened a large short position to inflate the vault’s AUM, then redeemed GLP at the manipulated higher value to drain funds.
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Exploited Contract (GMX: Order Book on Arbitrum): 0x09f77e8a13de9a35a7231028187e9fd5db8a2acb
Exploited Contract (GMX: Vault on Arbitrum): 0x489ee077994b6658eafa855c308275ead8097c4a
On June 21, the Hacken exploit on the Ethereum mainnet resulted in a $250K loss due a minter wallet key compromise. The attacker was able to mint HAI tokens and exchanged them for profit. Hacken team acknowledged the incident and confirmed that the deployer wallet and core infrastructure were not affected. Hacken has stopped minting and is improving its bridge architecture to prevent future risks.
On June 19, the BankrollNetworkStack exploit on Ethereum and BNB chains resulted in a $65K loss. The root cause of the exploit was an integer underflow in the sell() function, where a signed integer was subtracted without safety checks: payoutsTo[_customerAddress] -= _updatedPayouts. The contract was compiled with Solidity 0.6.8, which lacks overflow/underflow protection. The attacker exploited this flaw to manipulate dividend accounting and withdraw more funds than allowed.
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Exploited Contract (on BNB): 0xAdEfb902CaB716B8043c5231ae9A50b8b4eE7c4e
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Follow-up: Conduct a follow-up review to ensure that the remediation steps were effective and that the smart contract is now secure.
Follow-up: Conduct a follow-up review to ensure that the remediation steps were effective and that the smart contract is now secure.
In Brief
Remitano suffered a $2.7M loss due to a private key compromise.
GAMBL’s recommendation system was exploited.
DAppSocial lost $530K due to a logic vulnerability.
Rocketswap’s private keys were inadvertently deployed on the server.
Hacks
Hacks Analysis
Huobi | Amount Lost: $8M
On September 24th, the Huobi Global exploit on the Ethereum Mainnet resulted in a $8 million loss due to the compromise of private keys. The attacker executed the attack in a single transaction by sending 4,999 ETH to a malicious contract. The attacker then created a second malicious contract and transferred 1,001 ETH to this new contract. Huobi has since confirmed that they have identified the attacker and has extended an offer of a 5% white hat bounty reward if the funds are returned to the exchange.
