Summary

Users may lose access to their NFTs if the L1-L2 collection mapping is changed after initial bridging, particularly if a new L2 collection is deployed and mapped to the existing L1 collection.

Vulnerability Details

1. Users bridge NFTs from L1 to L2, with a new ERC721 contract deployed on L2.

2. Later, the L1 collection owner deploys their own NFT collection on L2.

3. The ArkProject owner updates the L1-L2 mapping to point to the new L2 collection.

4. Users who previously bridged NFTs can no longer bridge back to L1, as their NFTs are in the old L2 collection.

Impact

Users lose access to their bridged NFTs on L2.

Tools Used

Manual review

Recommendations

1. Implement a migration system for NFTs when L1-L2 mappings change.

2. Add functionality to bridge back NFTs to L1 and then to the correct L2 collection.