Core Contracts

Summary

The RToken contract's burn function incorrectly uses rayMul instead of rayDiv when calculating the scaled amount, resulting in inflated burn values that cause users to lose funds by burning more RTokens than necessary for the same amount of underlying assets. This benefits the protocol and remaining RToken holders at the expense of users performing burns.

Vulnerability Details

The calculation multiplies the amount by the index instead of dividing it. Since the liquidity index typically grows over time and is greater than 1 RAY, this results in an inflated amountScaled value.

Example:

• Amount to burn: 100 asset tokens

• Current index: 2.0 RAY

• Current calculation of RTokens: 100 * 2.0 = 200 (incorrect)

• Expected calculation of RTokens: 100 / 2.0 = 50 (correct)

Impact

HIGH - Users are losing more Tokens than intended.

1. Users burning RTokens lose significant value

2. Less underlying tokens received per RToken burned

3. The loss increases as the liquidity index grows over time

4. The protocol unfairly gains value at the expense of users

Recommendations

Replace the rayMul operation with rayDiv