Ethena Labs - critical-or-high's results

Lines of code

https://github.com/code-423n4/2023-10-ethena/blob/main/contracts/StakedUSDe.sol#L191

Vulnerability details

Impact

An attacker could make staked USDE contract unusable by donating dust amount of USDE (asset tokens) just right after StakedUSDeV2 creation. Thus discouraging users from staking USDE.

StakedUSDe is a modified version of ERC4626, while it employs a tailored mechanism to protect from frontrunning with a "donation" attack.

The protection mechanism (the _checkMinShares() function) ensures that the total supply is greater than MIN_SHARES = 1 ETH.

  /// @notice ensures a small non-zero amount of shares does not remain, exposing to donation attack
  function _checkMinShares() internal view {
    uint256 _totalSupply = totalSupply();
    if (_totalSupply > 0 && _totalSupply < MIN_SHARES) revert MinSharesViolation();
  }

This leads to the following DoS attack via dust USDE donation:

1. An attacker donates 1 Gwei of USDE to the StakedUSDeV2 contract after its deployment.
2. A legitimate user tries to deposit 10_000 USDE.
3. The previewDeposit() function returns the amount of shares 10_000 * 10^18 * (1 / 10^9) which is less than MIN_SHARES = 10^18 and call to deposit() reverts.
4. Since it's not possible to use StakedUSDeV2, a new StakedUSDeV2 should be deployed. An attacker repeats steps 1-3.

Proof of Concept

• https://github.com/code-423n4/2023-10-ethena/blob/main/contracts/StakedUSDe.sol#L191
• https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/extensions/ERC4626.sol#L229

Tools Used

Manual review.

Recommended Mitigation Steps

Use ERC4626.sol built-in protection mechanism from frontrunning with a "donation" attack instead of _checkMinShares().

Assessed type

DoS

Lines of code

https://github.com/code-423n4/2023-10-ethena/blob/main/contracts/StakedUSDeV2.sol#L116

Vulnerability details

Impact

Functions StakedUSDev2.cooldownShares() and StakedUSDev2.cooldownAssets() allow someone to withdraw USDE on behalf of the owner in case the owner approves some amount of staked USDE to someone.

It allows such a person with approved staked USDE from the owner to grief them by calling periodically cooldownShares() or cooldownAssets() with one wei amount of shares/assets. As a result, the owner cannot withdraw their USDE by calling unstake().

When cooldownShares() or cooldownAssets() is called (on behalf of the owner) cooldowns[owner].cooldownEnd is re-written witn new value uint104(block.timestamp) + cooldownDuration. Because of that, the following condition is false and unstake() reverts.

Proof of Concept

• https://github.com/code-423n4/2023-10-ethena/blob/main/contracts/StakedUSDeV2.sol#L82
• https://github.com/code-423n4/2023-10-ethena/blob/main/contracts/StakedUSDeV2.sol#L100

Tools Used

Manual review.

Recommended Mitigation Steps

Implement a queue for the owner to withdraw USDE from USDeSilo.

Assessed type

DoS