Hawk High

Issue Summary

The LevelOne contract implements the UUPS upgradeable pattern but lacks the critical protective __gap array that safeguards against storage layout corruption during contract upgrades. This omission creates a significant vulnerability that could lead to catastrophic data loss or contract malfunction when upgrading.

Technical Details

When developing upgradeable contracts using OpenZeppelin's UUPS pattern, each contract in the inheritance chain should include a storage gap to reserve space for future variables. The gap serves as a buffer zone that can be consumed by future versions of the contract without affecting the storage layout of child contracts.

Current implementation:

The absence of this storage gap creates a brittle contract that cannot safely evolve over time. If any future versions of the imported OpenZeppelin contracts introduce new storage variables, they will occupy slots that were meant for LevelOne's own storage, causing a cascading corruption of data.

Impact - High

The consequences of this vulnerability include:

1. Data Integrity Loss: Critical contract state could become corrupted after an upgrade.

2. Functional Failure: Core contract functions may operate on incorrect data, leading to unexpected behaviors.

3. Financial Risk: Funds controlled by the contract could be misallocated or irretrievable if key storage variables (like principal or mapping data) are corrupted.

4. Upgrade Paralysis: Once recognized, this issue effectively prevents safe upgrades, defeating the purpose of making the contract upgradeable.

Likelihood - Medium to High

While the issue only materializes during an upgrade involving storage layout changes, such changes are common in contract evolution:

1. OpenZeppelin regularly updates their libraries

2. The contract design itself suggests future enhancements (educational system progression)

3. The UUPS pattern specifically exists to facilitate evolution

Given these factors, it's highly likely that an upgrade attempt will occur within the contract's lifetime, making this vulnerability probable to manifest.

Proof of Concept

Consider this simplified scenario:

1. Current version of parent contract:

   abstract contract UUPSUpgradeable {

   // Original storage variables

   }

2. Deploy LevelOne which inherits from this version.

3. Future version of parent contract:

   
   
   abstract contract UUPSUpgradeable {

   // Original storage variables

   uint256 newVariable1;

   address newVariable2;

   }

4. When upgrading to use this future version:

   • newVariable1 will collide with principal

   • newVariable2 will collide with inSession

   • The entire state becomes corrupted

Remediation

Implement a storage gap at the end of the contract:

The size of the gap (50 slots in this example) should be chosen based on anticipated future expansion needs. This simple addition drastically improves the contract's upgrade safety by providing a buffer zone for future parent contract modifications.

Additionally, consider implementing comprehensive upgrade tests that verify storage layout compatibility between versions before deploying upgrades to production.