Odaily Planet Daily reports that the ethFromDefund() pricing logic in the USM contract's defund() redemption function has a flaw. This function calculates the consideration using the arithmetic average of the current FUM sell price and the estimated final FUM sell price in a single redemption. However, this algorithm lacks split invariance. When combined with the state contraction factor adjShrinkFactor and integer truncation mechanism associated with each redemption, splitting an equal amount of FUM assets into 64 smaller redemptions results in a significantly higher total amount of ETH withdrawn compared to a single large redemption.
USM Contract Vulnerability Leads to Theft of 70.83 ETH
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Summary
A vulnerability in the USM contract’s defund() function resulted in the theft of 70.83 ETH. The ethFromDefund() pricing logic uses an arithmetic average of FUM sell prices, lacking split invariance. Attackers exploited this by splitting redemptions into 64 small transactions. The flaw, combined with adjShrinkFactor and integer rounding, enabled disproportionate ETH extraction. Traders are now monitoring how this impacts the ETH price and which altcoins to watch in the coming days.
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