On August 9, 2026, USM on Ethereum was exploited via an arithmetic error in its token accounting logic, resulting in a loss of approximately $136,000. Flagged by SlowMist; no dedicated post-mortem has been published.

The USM protocol suffered an exploit due to a pricing logic flaw in the ethFromDefund() function within defund(). It uses the arithmetic mean of the current and estimated final FUM sell prices for a single redemption but lacks “split invariance.” Combined with the per-redemption state contraction (adjShrinkFactor) and integer rounding, an attacker used a flash loan to call fund() to manipulate internal pricing, then split the same FUM amount into 64 small defund() calls, extracting more ETH than a single large call and causing a loss of ~70.83 ETH.