`swapSource` in `RNSourceController` contract can be frontrunned and eventually lead to a DoS

[code423n4]

Lines of code

https://github.com/code-423n4/2023-03-wenwin/blob/main/src/RNSourceController.sol#L89-L104

Vulnerability details

Impact

A malicious randon source con frontrun calls to swapSource and prevent protocol owners from changing the random source by frontrunning the call with a transaction to onRandomNumberFulfilled which effectively resets the failedSequentialAttempts to zero, making the original call to swapSource revert.

This process can be repeated any number of times, eventually leading to a DoS and the impossibility of changing the random source.

Proof of Concept

1. Source timeouts and doesn't return request response, retry is called until failedSequentialAttempts == maxFailedAttempts.
2. Protocol owners call swapSource to change the random source of the contract
3. Current random source frontruns the call with a call to onRandomNumberFulfilled which resets the failedSequentialAttempts back to 0.
4. Original transaction from (2) gets reverted as failedSequentialAttempts is now less than maxFailedAttempts.

Recommendation

In case of maxFailedAttempts enter a more robust "pause" state that lets protocol owners deal better with the current situation.

[c4-judge]

thereksfour changed the severity to QA (Quality Assurance)

[c4-judge]

thereksfour marked the issue as grade-a

[rand0c0des]

This is highly unlikely with ChainLink VRFv2. However, seems like a valid concern.

[c4-sponsor]

rand0c0des marked the issue as sponsor acknowledged