Root + Impact

If either collectionId or itemId is allowed to be 128 bits or greater, collisions can occur. For example:
(collectionId: 1, itemId: 0) → tokenId = 2^128
(collectionId: 0, itemId: 2^128) → tokenId = 2^128
Both pairs produce the same tokenId, meaning two different NFTs would be indistinguishable in the system.

Description

The contract uses the following logic to combine a collectionId and an itemId into a single ERC1155 token ID:

This is intended to uniquely encode a pair of 128-bit values into a single 256-bit value

Risk

Likelihood:

This bug can lead to loss of uniqueness, data corruption, and potential exploits.

Impact

• Token ID Collision:

Different (collectionId, itemId) pairs can map to the same tokenId.

• Loss of Uniqueness:

This breaks the uniqueness guarantee of token IDs, which can lead to:

• Incorrect ownership tracking

• Metadata confusion

• Potential exploits (e.g., minting or transferring unintended NFTs)

Recommended Mitigation

Enforce 128-bit Limits:

Add require statements to ensure both collectionId and itemId are strictly less than 2^128: