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fix(H5): mark wstETH at the Lido exchange rate, not the DEX spot - #16
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Audit H5: wstethUsdWad marked wstETH at the lower of the exchange rate and the instantaneous UniV3 slot0 spot. slot0 is flash-loan manipulable within a block, and because it was the lower-of, an attacker could push the mark DOWN (front-run settleEpoch, depress the pool, mint extra shares cheaply, back-run) to skew share pricing. Fix: mark wstETH purely at stEthPerToken x ETH/USD, the fundamental redemption value and the standard wstETH-collateral marking (Aave/Morpho). It is not flash-manipulable, so it cannot skew NAV or settlement pricing. The pool spot is kept ONLY as a depeg gate on BUYING more wstETH (wstethBuyAllowed), where a manipulated spot is fail-safe: it can only block a buy, never inflate value. Regression: a basis breach keeps the mark at the exchange rate while blocking buys; an extreme flash-pushed pool spot leaves the mark unchanged. 116 -> 117.
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Audit finding H5 (High)
wstethUsdWad()marked wstETH at the lower of the Lido exchange rate and the instantaneous UniV3slot0spot.slot0is flash-loan manipulable within one block, and because it was the lower-of, an attacker could only push the mark down (front-runsettleEpoch, depress the pool, mint extra shares cheaply, back-run), skewing share pricing. That mark feeds NAV and settlement directly.Fix
Mark wstETH purely at
stEthPerToken x ETH/USD(the Lido exchange rate). This is the fundamental redemption value (wstETH -> stETH -> ETH), is not flash-manipulable, and is the standard wstETH-collateral marking used by Aave and Morpho. Chosen over an on-chain UniV3 TWAP because it is materially lower-risk (no TickMath vendoring, where a wrong constant would silently mis-price). The pool spot is retained only inwstethBuyAllowedas a depeg gate on buying more wstETH, where a manipulated spot is fail-safe: it can only block a buy, never inflate value.Trade-off noted: during a real severe wstETH market depeg, NAV marks wstETH at redemption value rather than the discounted market price. The wstETH sleeve is capped at 50% and defaults to 0, and the buy gate still prevents adding wstETH during a depeg.
Tests
test_h5_basisBreach_marksAtRate_blocksBuys: a 5% pool depeg keeps the mark at the exchange rate but blocks buys.test_h5_poolPushDownCannotLowerTheMark: an extreme flash-pushed pool spot leaves the value mark unchanged.Independent of the other PRs; branches off main. Suite 116 -> 117.