Exercise 5

Table of contents:

• Exercise 5
  • Setup
  • Context
  • Goals
  • Hints
  • Solution

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Setup

1. Clone the repo: git clone https://github.com/crytic/damn-vulnerable-defi-echidna
2. Install the dependencies by running yarn install.

Context

The challenge is described here: https://www.damnvulnerabledefi.xyz/challenges/2.html. It is assumed that the reader is familiar with the challenge.

Goals

• Set up the testing environment with the correct contracts and necessary balances.
• Analyze the "before" function in test/naive-receiver/naive-receiver.challenge.js to identify the required initial setup.
• Add a property to check if the balance of the FlashLoanReceiver contract can change.
• Create a config.yaml with the necessary configuration option(s).
• Once Echidna finds the bug, fix the issue and re-test your property with Echidna.

The following contracts are relevant:

• contracts/naive-receiver/FlashLoanReceiver.sol
• contracts/naive-receiver/NaiveReceiverLenderPool.sol

Hints

It is recommended to first attempt without reading the hints. The hints can be found in the hints branch.

• Remember that you might need to supply the test contract with Ether. Read more in the Echidna wiki and check the default config setup.
• The invariant to look for is that "the balance of the receiver contract cannot decrease."
• Learn about the allContracts optio.
• A template is provided in contracts/naive-receiver/NaiveReceiverEchidna.sol.
• A config file is provided in naivereceiver.yaml.

Solution

The solution can be found in the solutions branch.

echidna . --contract NaiveReceiverEchidna --config naivereceiver.yaml
...

echidna_test_contract_balance: failed!💥
  Call sequence:
    flashLoan(0x62d69f6867a0a084c6d313943dc22023bc263691,353073667)

...