On July 15, an attacker drained roughly $11.86 million in USDC from Ostium, a decentralized perpetuals exchange on Arbitrum, in a single transaction. The exploit bundled twenty calls into the protocol's trading contracts, alternating between the Trading contract and OstiumPrivatePriceUpKeep contract. The key move: the attacker submitted a fabricated BTC price of $5,000 to open a position and $60,000 to close it.
How the price got twisted
The transaction was one bundle of twenty calls, and the attacker's wallet had opened its first position minutes before with a rounding-error deposit. The target was pair index 0, which Ostium's subgraph maps to BTC/USD. The attacker didn't break the oracles themselves — they broke the authorization layer. Whoever is allowed to submit price reports effectively decides the settlement price, and that's what got used.
A protocol with real backing
Ostium has been a well-funded player in the perps space. It raised a $3.5 million seed in 2023 led by General Catalyst and LocalGlobe, with backers like SIG, DeFi Alliance, and Balaji Srinivasan. Then in December 2025 it added a $20 million Series A co-led by General Catalyst and Jump Crypto, putting total funding at roughly $27.8 million. At the time, Ostium advertised more than $25 billion in cumulative trading volume, including around $5 billion in metals. On the day of the exploit, DefiLlama showed TVL near $63 million.
The flaw wasn't the oracle
Ostium runs a pull-based oracle system: Stork Network for real-world asset feeds, Chainlink Data Streams for crypto pairs. The vulnerability wasn't in the data itself. It was in the price authorization. Whoever is authorized to submit price reports can decide the price used for settlement. That's how a BTC price of $5,000 and then $60,000 made it through. It's a design issue, not a data feed failure.
Still waiting on the final numbers
The exact authorization failure and the reconciled total loss aren't confirmed yet. That's up to Ostium's own accounting. Until then, the community is left with the question of how a single transaction with a fake price went through a protocol that had $63 million locked at the time.
