Beanstalk: The Finale

Summary

Beanstalk relies on Basin(Pump/Well) to read the prices and provide it to different components for instance: SeasonFacet, PipelineConvertFacet, LibWellBdv, LibWellMinting, LibDeltaB, etc.

The pump functions are based on the time-weighted price, returning the time-weighted average. For instance:

• readInstantaneousReserves

• readTwaReserves

• readCappedReserves

In the event that an L2's sequencer goes down, the time-weighted price when it comes back online will be the extrapolated previous price. This will create an opportunity to push through transactions at the old price before it is updated.

Impact

Even when the new price is read from the Pump, it will be assumed by the sequencer that the previous price held up until the moment it came back online, which will result in a slow, time-weighted adjustment back to the current price.

Reference of a similar issue: https://solodit.xyz/issues/h-01-univ3-oracle-unsafe-on-l2s-in-event-of-sequencer-downtime-zachobront-none-splits-oracle-markdown

Tools Used

Manual Review

Recommendations

Use the Chainlink Sequencer check before consuming the price from the Well/Pump.

https://docs.chain.link/data-feeds/l2-sequencer-feeds#example-code