## Description The drop chances defined in the state variables section for the COMMON and LEGENDARY are misleading. ## Vulnerability Details The 3 rarity scores are defined as follows: ``` uint256 public constant COMMON_RARITY = 70; uint256 public constant RARE_RARITY = 25; uint256 public constant LEGENDARY_RARITY = 5; ``` This implies that out of a really big number of NFT's, 70% should be of common rarity, 25% should be of rare rarity and the last 5% should be legendary. The `selectWinners` function doesn't implement these numbers. ``` uint256 rarity = uint256(keccak256(abi.encodePacked(msg.sender, block.difficulty))) % 100; if (rarity <= COMMON_RARITY) { tokenIdToRarity[tokenId] = COMMON_RARITY; } else if (rarity <= COMMON_RARITY + RARE_RARITY) { tokenIdToRarity[tokenId] = RARE_RARITY; } else { tokenIdToRarity[tokenId] = LEGENDARY_RARITY; } ``` The `rarity` variable in the code above has a possible range of values within [0;99] (inclusive) This means that `rarity <= COMMON_RARITY` condition will apply for the interval [0:70], the `rarity <= COMMON_RARITY + RARE_RARITY` condition will apply for the [71:95] rarity and the rest of the interval [96:99] will be of `LEGENDARY_RARITY` The [0:70] interval contains 71 numbers `(70 - 0 + 1)` The [71:95] interval contains 25 numbers `(95 - 71 + 1)` The [96:99] interval contains 4 numbers `(99 - 96 + 1)` This means there is a 71% chance someone draws a COMMON NFT, 25% for a RARE NFT and 4% for a LEGENDARY NFT. ## Impact Depending on the info presented, the raffle participants might be lied with respect to the chances they have to draw a legendary NFT. ## Recommendations Drop the `=` sign from both conditions: ```diff -- if (rarity <= COMMON_RARITY) { ++ if (rarity < COMMON_RARITY) { tokenIdToRarity[tokenId] = COMMON_RARITY; -- } else if (rarity <= COMMON_RARITY + RARE_RARITY) { ++ } else if (rarity < COMMON_RARITY + RARE_RARITY) { tokenIdToRarity[tokenId] = RARE_RARITY; } else { tokenIdToRarity[tokenId] = LEGENDARY_RARITY; } ```