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

User balances never updated

hongphat19

Root + Impact

Description

Users must pay at least 1 ETH when calling likeUser(). According to the README, if two users mutually like each other, all previous like payments, minus a 10% fee, should be pooled into a shared multisig wallet for the matched users.

The contract never credits msg.value to userBalances[msg.sender]. As a result, matchRewards() always reads zero balances, sends zero ETH to the multisig, records zero protocol fees, and leaves the paid ETH trapped in LikeRegistry.

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");
​
// @> msg.value is accepted but never added to userBalances[msg.sender]
likes[msg.sender][liked] = true;
emit Liked(msg.sender, liked);
​
if (likes[liked][msg.sender]) {
matches[msg.sender].push(liked);
matches[liked].push(msg.sender);
emit Matched(msg.sender, liked);
matchRewards(liked, msg.sender);
}
}
​
function matchRewards(address from, address to) internal {
// @> These values remain zero because likeUser never updates userBalances
uint256 matchUserOne = userBalances[from];
uint256 matchUserTwo = userBalances[to];
userBalances[from] = 0;
userBalances[to] = 0;
​
uint256 totalRewards = matchUserOne + matchUserTwo;
uint256 matchingFees = (totalRewards * FIXEDFEE) / 100;
uint256 rewards = totalRewards - matchingFees;
totalFees += matchingFees;
​
MultiSigWallet multiSigWallet = new MultiSigWallet(from, to);
(bool success,) = payable(address(multiSigWallet)).call{value: rewards}("");
require(success, "Transfer failed");
}

Risk

Likelihood:

  • This occurs during every paid like because likeUser() accepts ETH without recording it.

  • This occurs during every mutual match because matchRewards() relies entirely on userBalances.

Impact:

  • Matched users receive zero ETH in their shared multisig instead of their pooled like payments.

  • Paid ETH remains stuck in LikeRegistry because totalFees also stays zero and withdrawFees() can only withdraw tracked fees.

Proof of Concept

function testLikePaymentsAreNotCreditedAndBecomeStuck() public {
SoulboundProfileNFT nft = new SoulboundProfileNFT();
LikeRegistry registry = new LikeRegistry(address(nft));
​
address alice = address(0xA11CE);
address bob = address(0xB0B);
vm.deal(alice, 2 ether);
vm.deal(bob, 2 ether);
​
vm.prank(alice);
nft.mintProfile("Alice", 25, "ipfs://alice");
​
vm.prank(bob);
nft.mintProfile("Bob", 26, "ipfs://bob");
​
vm.prank(alice);
registry.likeUser{value: 1 ether}(bob);
​
assertEq(registry.userBalances(alice), 0);
assertEq(address(registry).balance, 1 ether);
​
vm.prank(bob);
registry.likeUser{value: 1 ether}(alice);
​
assertEq(registry.userBalances(alice), 0);
assertEq(registry.userBalances(bob), 0);
assertEq(address(registry).balance, 2 ether);
​
vm.expectRevert("No fees to withdraw");
registry.withdrawFees();
}

Recommended Mitigation

Credit the incoming like payment before checking for a mutual match.

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");
​
+ userBalances[msg.sender] += msg.value;
likes[msg.sender][liked] = true;
emit Liked(msg.sender, liked);
​
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 hours 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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