immunefi-team / community-challenges Goto Github PK

The POC for the RareNFT assumes that the nonce doesn't change between the off-chain reading and the on-chain attack but that's unrealistic when there are other users.
Luckily, the nonce and the latest token id are in sync, and the latest id can be deduced on-chain in O(logN) time, where N is the number of users who called mint after we read nonce.
edit: Actually, MockERC721.nftId is public so we can just read it in O(1).

The results in: https://github.com/immunefi-team/community-challenges/pull/7/checks say:

You are using a version of Node.js that is not supported by Hardhat, and it may work incorrectly, or not work at all.
Please, upgrade your Node.js version.

Shouldn't we do that?

Challenge 6 (KYC) is not about signature malleability, which would consist in changing the signature without invalidating it. (Something is malleable if you can change its shape without breaking it.)
In this challenge, any invalid signature will do. There's no need to start from a valid signature and alter the last byte. In a minimal POC a user deploys an app and the attacker calls onboardWithSig using a 0 signature. That's it!

Taking the situation of feeExempt as an example:
wipeout = uint248((tokenBalance * rewardBalance + lastReward * stake) / (stake - tokenBalance))
The above expression is equivalent to:
(wipeout + rewardBalance) = (wipeout - lastReward) * stake / tokenBalance
The left side of the equation represents the total reward(including we added) we need to receive, which is correct.
But there seems to be a issue on the right side of the equation, it should be the actual reward through calling sendReward function.
It is calculated through the following code:

amount = _tokenInfo.totalReward - _stakerInfo.lastReward; // line-1
if (balance != 0) {
    amount = (amount * staked) / balance; 
}

As line-1 shows, actually wipeout shouldn't be _TokenInfo.totalReward, which should be _TokenInfo.totalReward -_ StacerInfo.lastReward. _tokenInfo.totalReward - _stakerInfo.lastReward means the value added by calling function addReward, which is wipeout.
So I think the correct equation may be (wipeout + rewardBalance) = wipeout * stake / tokenBalance, which can be used to derive the actual expression of wideout as (tokenBalance * rewardBalance) / (staked - tokenBalance).
Of course, it's also possible that I misunderstood. Please help me correct it.