- Ostium, a decentralized perpetual futures exchange on Arbitrum, was hacked via a private key compromise of its oracle signer, with losses estimated between $18 million and $23 million.
- The attacker exploited self‑signed favorable prices to drain approximately $11.86 million USDC from the OLP vault, which serves as the protocol’s settlement layer.
- The incident follows similar oracle‑based exploits on Bonzo Finance ($9 million) and Summer Finance ($6 million), the latter now winding down.
- DeFi losses in the first half of 2026 exceeded $900 million across 87 incidents, with over 80% caused by compromised private keys or bridge hacks.
Ostium, a decentralized perpetual futures exchange running on Arbitrum, was hacked through a suspected private key compromise of its oracle signer, according to multiple security firms that flagged suspicious outflows. Loss estimates range from $18 million to over $23 million.
Shortly after, Ostium’s official X account confirmed an “issue” with its OLP vault and stated it had paused all trading while the team investigates. The OLP vault acts as the protocol’s settlement layer, where users deposit USDC to open trades.
Decurity explained that the attacker fed self‑signed favorable prices to open and immediately close trades at a profit, draining approximately $11.86 million USDC from the vault. Ostium held about $63 million in total assets before the exploit, data from DeFiLlama shows.
This loss comes just four days after Bonzo Finance on Hedera lost $9 million due to an exposed price oracle. Last week, Summer Finance was hacked via a similar price manipulation attack, losing $6 million, and announced it will wind down because it cannot recover.
In the first half of 2026, the DeFi sector lost over $900 million in 87 incidents, according to a report; more than 80% of losses came from compromised private keys or bridge hacks. Two large incidents — Drift Protocol and LayerZero/KelpDAO — made up the majority, prompting Arbitrum’s Security Council to freeze over $70 million of stolen funds. It remains to be seen whether Ostium’s loss will trigger a similar response.
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