# Smart Contract Security Lab

This folder contains intentionally vulnerable contracts and tests that exploit
them. The goal is to learn how bugs work so you can review and defend contracts
more effectively.

Never deploy these contracts outside a local devnet.

## Current Exercises

### Reentrancy

Files:

- `src/security/VulnerableBank.sol`
- `test/security/Reentrancy.t.sol`

The vulnerable contract sends ETH to the caller before updating internal
balances. The attacker contract re-enters `withdraw` from its `receive`
function and drains more ETH than it deposited.

Run:

```bash
./jeannie blockchain-test test/security/Reentrancy.t.sol -vv
```

Defensive fixes to practice:

- checks-effects-interactions
- reentrancy guards
- pull-payment patterns
- avoiding unnecessary raw calls
- invariant tests for total balances

## Suggested Next Exercises

- bad access control
- `tx.origin` authentication
- signature replay without chain ID or nonce
- oracle price manipulation simulation
- unsafe upgradeable proxy ownership