Worked example · 2026-10

Set Protocol — actualizeFee() rounded unit shares up by one with no fee minted, and issue-then-redeem pocketed the difference — Set Protocol vault / Ethereum — 2026-10-06

Loss

~5.08 ETH (~$13.7K), per SlowMist.

OAK Techniques observed

OAK-T9.011 (Precision-Loss / Rounding Attack — primary, per SlowMist. actualizeFee() recalculated unitShares with upward rounding even though no fee was minted, moving it from 4,927 to 4,928. The attacker issued set tokens before the update and redeemed the same quantity after it, taking the collateral created by the one-unit increase; Uniswap v4 flash accounting supplied temporary liquidity to scale it. See techniques/T9.011-precision-loss-rounding-attack.md).

Attribution

pseudonymous.

Key teaching point

Round against the caller, and do not recompute when nothing changed. A no-op fee update that still re-rounds a per-unit value hands a free unit to anyone who can straddle it; flash liquidity turns one unit into a payable amount.