Ostium, a decentralized perpetual futures exchange, has been hacked on the Arbitrum network via a suspected private key compromise of its oracle signer.
A number of crypto security firms flagged suspicious outflows, with estimates loss estimates ranging from $18 to over $23 million.
Ostium’s official X account confirmed an “issue” with its OLP vault shortly thereafter.
Read more: Supra patched oracle on 11 other chains before $9M Hedera exploit
Ostium allows for trading perpetual futures of stocks, commodities, and forex, and held approximately $63 million of assets, pre-hack, according to DeFiLlama data.
Its OLP vault acts as the protocol’s settlement layer, into which users deposit USDC to open trades on the platform.
Decurity, highlighting an example transaction, explained that “the attacker fed self-signed favorable prices to open and immediately close trades at a profit, draining ~11.86M USDC from the OstiumVault.”
Read more: Cap ‘stabledrop’ U-turn sees cUSD drop $23M, founder denies self dealing claims
DeFi dangers
The loss comes just four days after $9 million was lost from Bonzo Finance on the Hedera network, also due to an exposed price oracle.
Supra, the firm behind the vulnerable oracle had previously patched deployments on 11 other chains in the days leading up to the exploit.
Last week, Summer Finance was hacked, also via a price manipulation attack, losing $6 million. It’s announced today that it will not be able to recover from the incident and will be winding down.
Read more: DeFi platform Summer Finance loses $6M in vault exploit
In the first half of 2026, the DeFi sector has seen over $900 million lost in 87 incidents, with over 80% of the losses caused by compromised private keys or bridge hacks.
Of these, two incidents make up the majority, Drift Protocol and LayerZero/KelpDAO. Following the latter, the contagion threat led Arbitrum’s Security Council to step in and freeze over $70 million of stolen funds.
It remains to be seen whether Ostium’s loss warrants a similar reaction.
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