[ARFC] Add rsETH to Aave V3 Ethereum

Governance New Asset
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LlamaRisk is in favour of @ChaosLabs’s recommendation for cautious onboarding of Kelp’s rsETH, including exclusion from e-Mode (as opposed to weETH and osETH), a limited supply cap of 8,000 rsETH, and a conservative LT of 75%. This recommendation stems from our initial review of rsETH, with a particular focus on its internal exchange rate (probed by @MarcZeller), and associated dependancies.

We share our preliminary findings below, emphasizing using rsETH market price for its integration with Aave. We are working on a comprehensive assessment of rsETH and will update the Aave community accordingly.

rsETH Exchange Rate Mechanism

The rsETH exchange rate is determined by the underlying assets (ETH, stETH, ETHx, sfrxETH) and the accumulated staking rewards. The LRTOracle contract stores the Oracle contract for each asset.

  • stETH (oracle contract): price is hardcoded to 1:1 with ETH.
  • ETHx (oracle contract): price relies on the getExchangeRate function of the StaderStakePoolsManager contract, which Stader updates via a permissioned function. The oracle does not independently check for price anomalies or liveness, and it is a proxy contract that the Stader team can upgrade. The getExchangeRate function, operated by Stader, returns a state variable called exchangeRate, updated by the submitExchangeRateData function, callable only by whitelisted addresses controlled by Stader. The ETHx price is determined by the “book value” of ETHx, calculated as totalAssets / totalSupply, similar to the ERC-4626 accounting method.
  • sfrxETH (oracle contract): price is obtained from Frax’s sfrxETH pricePerShare function, an ERC-4626 tokenized vault. The price feed assumes frxETH to be 1:1 with ETH.

Market Price vs. rsETH exchange rate

The rsETH exchange rate calculation includes several assumptions, resulting in a considerable spread between the computed exchange rate and the market price of rsETH. This can be seen in the chart below (data from March 8th May 31st):

image
Source: rsETH internal rate, Redstone & Chainlink feeds and Uniswap V3 rsETH / ETH Pool (blocks 19390000 to 19987000)

Risks with dependencies

The main risk factors associated with rsETH’s dependencies are:

  1. sfrxETH/stETH oracle assumptions: If the market price of stETH or frxETH falls below the ETH price, the collateral backing rsETH could be worth less than expected by the rsETH system. This could lead to a depreciation in the market price of rsETH.
  2. ETHx oracle centralization: The ETHx price is obtained from a relatively centralized source. If a malicious actor manipulates the price feed, they could unjustly inflate the rsETH supply up to the ETHx deposit limit.
  3. LRTManager permissioned function: The Kelp External Admin (6/8) is whitelisted as the LRTManager, which can updatePriceOracleFor without a timelock. This centralization could lead to mistakes or malicious actions that could brick the protocol or cause a loss of funds. For example, adding a new supported token requires calling three different functions in a specific sequence. If the calls are contained in other transactions, the protocol could be in an intermediate state, blocking the updateRSETHPrice() function.
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