DatingDapp

Summary

The executeTransaction function in the MultiSigWallet contract is vulnerable to reentrancy attacks because it makes an external call (call{value: txn.value}) before updating state variables or emitting events. A malicious contract can re-enter and potentially trigger another transaction execution before the first one completes, leading to double execution or unexpected state changes.

Vulnerability Details

Code Snippet:

Exploit Scenario

1. Attacker creates a malicious contract that has a fallback function capable of re-entering executeTransaction.

2. The attacker gets a transaction approved and calls executeTransaction.

3. The external .call{value: txn.value} sends funds to the attacker's contract.

4. The attacker's fallback function re-enters executeTransaction before the first call completes, executing the same transaction multiple times before txn.executed = true takes effect.

5. The attacker withdraws multiple times, effectively draining funds.

PoC:

Impact

Medium Severity: Attackers can re-enter executeTransaction before state changes take effect, leading to double execution or fund loss.
Funds Drain: If the attacker controls an approved transaction, they can continuously withdraw funds by exploiting the reentrancy loophole.
Broken MultiSig Security: A compromised owner or an attacker can bypass the intended transaction execution logic.

Tools Used

Slither (automated static analysis)
Manual Review (to confirm reentrancy risk)

Recommendations

To prevent reentrancy, follow the Checks-Effects-Interactions pattern by:

1. Updating state before making external calls (✅ Already done in this case).

2. Emitting events before making external calls (❌ Currently incorrect).

3. Using OpenZeppelin's ReentrancyGuard to prevent reentrancy.

Additional Considerations:

1. Use ReentrancyGuard (nonReentrant modifier) to prevent multiple function calls in the same transaction.

2. Emit events before external calls to ensure state consistency.

3. Limit gas for external calls to prevent complex fallback function execution.

4. By implementing these fixes, executeTransaction will be secured against reentrancy attacks and prevent potential fund loss or double execution exploits.