DatingDapp
AI First Flight #6
Beginner FriendlyFoundrySolidityNFT
EXP
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Submission Details
Severity: high
Valid

HIGH-02 — userBalances never updated, ETH permanently locked

goat

HIGH-02 — userBalances never updated, ETH permanently locked

Description

  • likeUser accepts ETH (msg.value >= 1 ether) but never assigns it to userBalances. When a match occurs, matchRewards reads both users' balances which are always 0, meaning the MultiSig receives 0 ETH while all ETH sent by users is permanently locked in LikeRegistry.

function likeUser(address liked) external payable {
require(msg.value >= 1 ether, "Must send at least 1 ETH");
// @> msg.value never assigned to userBalances!
likes[msg.sender][liked] = true;
}
​
function matchRewards(address from, address to) internal {
uint256 matchUserOne = userBalances[from]; // @> always 0
uint256 matchUserTwo = userBalances[to]; // @> always 0

Risk

Likelihood:

  • Occurs on every single match — 100% of cases.

Impact:

  • All ETH sent by users is stuck in the contract forever. Match rewards are always zero. Users lose funds with no way to recover them.

Proof of Concept

// Alice calls likeUser{value: 1 ether}(Bob)
// Bob calls likeUser{value: 1 ether}(Alice) → match triggered
// matchRewards reads userBalances[Alice] = 0, userBalances[Bob] = 0
// MultiSig receives 0 ETH
// 2 ETH stuck in LikeRegistry forever

Recommended Mitigation

function likeUser(address liked) external payable {
require(msg.value >= 1 ether, "Must send at least 1 ETH");
+ uint256 fee = (msg.value * FIXEDFEE) / 100;
+ userBalances[msg.sender] += msg.value - fee;
+ totalFees += fee;
​
require(!likes[msg.sender][liked], "Already liked");
// ...
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge 8 days ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-01] After the user calls the `likeUser` function, the userBalance does not increase by the corresponding value.

## Description User A calls `likeUser` and sends `value > 1` ETH. According to the design of DatingDapp, the amount for user A should be accumulated by `userBalances`. Otherwise, in the subsequent calculations, the balance for each user will be 0. ## Vulnerability Details When User A calls `likeUser`, the accumulation of `userBalances` is not performed. ```solidity function likeUser( address liked ) external payable { require(msg.value >= 1 ether, "Must send at least 1 ETH"); require(!likes[msg.sender][liked], "Already liked"); require(msg.sender != liked, "Cannot like yourself"); require(profileNFT.profileToToken(msg.sender) != 0, "Must have a profile NFT"); require(profileNFT.profileToToken(liked) != 0, "Liked user must have a profile NFT"); likes[msg.sender][liked] = true; emit Liked(msg.sender, liked); // Check if mutual like if (likes[liked][msg.sender]) { matches[msg.sender].push(liked); matches[liked].push(msg.sender); emit Matched(msg.sender, liked); matchRewards(liked, msg.sender); } } ``` This will result in `totalRewards` always being 0, affecting all subsequent calculations: ```solidity uint256 totalRewards = matchUserOne + matchUserTwo; uint256 matchingFees = (totalRewards * FIXEDFEE ) / 100; uint256 rewards = totalRewards - matchingFees; totalFees += matchingFees; ``` ## POC ```solidity function testUserBalanceshouldIncreaseAfterLike() public { vm.prank(user1); likeRegistry.likeUser{value: 20 ether}(user2); assertEq(likeRegistry.userBalances(user1), 20 ether, "User1 balance should be 20 ether"); } ``` Then we will get an error: ```shell [FAIL: User1 balance should be 20 ether: 0 != 20000000000000000000] ``` ## Impact - Users will be unable to receive rewards. - The contract owner will also be unable to withdraw ETH from the contract. ## Recommendations Add processing for `userBalances` in the `likeUser` function: ```diff function likeUser( address liked ) external payable { require(msg.value >= 1 ether, "Must send at least 1 ETH"); require(!likes[msg.sender][liked], "Already liked"); require(msg.sender != liked, "Cannot like yourself"); require(profileNFT.profileToToken(msg.sender) != 0, "Must have a profile NFT"); require(profileNFT.profileToToken(liked) != 0, "Liked user must have a profile NFT"); likes[msg.sender][liked] = true; + userBalances[msg.sender] += msg.value; emit Liked(msg.sender, liked); [...] } ```

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