What happened
A flash-loan-funded transaction drained 70.830977 ETH from the USM/FUM pool on Ethereum on 9 August 2026, estimated at about $136,124 at the on-chain USM oracle price.
Technical root cause
Fund and defund pricing used non-invariant-preserving average-price calculations.
How it happened
- The attacker flash-borrowed WETH, called
fund()to mint FUM, then split the newly minted FUM across 64defund()calls. - The pricing paths were not exact inverses, allowing the aggregate redemption to exceed the ETH deposited before the flash loan was repaid.
Protocol details
Classification
Token & Share Accounting
Protocol Type
DeFi Protocol
Implementation language
Solidity
Exploit Transaction
0xfae5e751b8ce01457c…cf559b050e
Evidence
- analysis USM/FUM Exploit Analysis anomly.rs
- analysis DeFiLlama defillama.com
Understand the attack patterns
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