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sherlock-audit / 2023-06-tokemak-judging

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carrotsmuggler - Slashing during `LSTCalculatorBase.sol` deployment can show bad apr for months #824

Open sherlock-admin opened 1 year ago

sherlock-admin commented 1 year ago

carrotsmuggler

medium

Slashing during LSTCalculatorBase.sol deployment can show bad apr for months

Summary

Slashing during LSTCalculatorBase.sol deployment can show bad apr for months

Vulnerability Detail

The contract LSTCalculatorBase.sol has some functions to calculate the rough APR expected from a liquid staking token. The contract is first deployed, and the first snapshot is taken after APR_FILTER_INIT_INTERVAL_IN_SEC, which is 9 days. It then calculates the APR between the deployment and this first snapshot, and uses that to initialize the APR value. It uses the function calculateAnnualizedChangeMinZero to do this calculation.

The issue is that the function calculateAnnualizedChangeMinZero has a floor of 0. So if the backing of the LST decreases over that 9 days due to a slashing event in that interval, this function will return 0, and the initial APR and baseApr will be set to 0.

The calculator is designed to update the APR at regular intervals of 3 days. However, the new apr is given a weight of 10% and the older apr is given a weight of 90% as seen below.

return ((priorValue * (1e18 - alpha)) + (currentValue * alpha)) / 1e18;

And alpha is hardcoded to 0.1. So if the initial APR starts at 0 due to a slashing event in the initial 9 day period, a large number of updates will be required to bring the APR up to the correct value.

Assuming the correct APR of 6%, and an initial APR of 0%, we can calculate that it takes upto 28 updates to reflect close the correct APR. This transaltes to 84 days. So the wrong APR cann be shown for upto 3 months. Tha protocol uses these APR values to justify the allocation to the various protocols. Thus a wrong APR for months would mean the protocol would sub optimally allocate funds for months, losing potential yield.

Impact

The protocol can underperform for months due to slashing events messing up APR calculations close to deployment date.

Code Snippet

https://github.com/sherlock-audit/2023-06-tokemak/blob/main/v2-core-audit-2023-07-14/src/stats/calculators/base/LSTCalculatorBase.sol#L108-L110

Tool used

Manual Review

Recommendation

It is recommended to initialize the APR with a specified value, rather than calculate it over the initial 9 days. 9 day window is not good enough to get an accurate APR, and can be easily manipulated by a slashing event.

codenutt commented 1 year ago

This behavior is acceptable. If we happen to see a slash > 12 bps over the initial 9 days, yes, we set it to 0. It increases the ramp time for that LST so pools with that LST will be set aside for a while until some APR (incentive, etc) comes up. For larger slashes that are more material (> 25bps), we have a 90 day penalty anyway.