Beanstalk: Dive Into Basin

Summary

In Solidity, the maximum value for a uint256 is 2^256 - 1. An overflow occurs when a calculation results in a number higher than this maximum value.

Vulnerability Details

For the calcReserve() function, the overflow scenario in the exponentiation step (lpTokenSupply ** 2) would occur if the lpTokenSupply is large enough that squaring it exceeds 2^256 - 1.

calcReserve()

The relevant line is this:

Let's consider a scenario:

• Let lpTokenSupply be x.

• The maximum value before overflow upon squaring would be the square root of 2^256 - 1, which is approximately 2^128.

• If lpTokenSupply (x) is greater than 2^128, then x * x would result in a number larger than 2^256 - 1, causing an overflow.

For example, if lpTokenSupply is 2^130, then squaring it (2^130 * 2^130) would result in 2^260, which is greater than 2^256 - 1, leading to an overflow.

Impact

Revert Transaction: Solidity 0.8.x automatically reverts the transaction if an arithmetic operation overflows.

Tools Used

Manual Review

Recommendations

• Input Validation:

Ensure that lpTokenSupply is within a range that, when squared, does not exceed the maximum uint256 value.