Beedle - Oracle free perpetual lending

Summary

If a borrower is refinancing to a lender said lender can front run the borrower's call with a call to updateInterestRate() to increase the interest rate. The borrower would then have a loan with an interest rate he didn't agree to.

Vulnerability Details

1. A customer sees lender B's pool's low-interest rate and calls refinance to change from his current lender, lender A, to lender B.

2. Lender B front runs customers call with a call to updateInterestRate to increase the interest rate

3. Customers call to refinance succeed but with a higher interest rate than the customer expected

Impact

refinance() doesn’t make sure the interest rate is what the borrower wants.
This is important since a lender can front-run the borrower's call to refinance with a call to setPool() to increase the interest rate.

Tools Used

manual

Recommendations

Allow borrower to pass in maxInterestRate