Cardano Vulnerabilities Game — Capture the Flag (CTF)

Welcome to the Cardano Capture the Flag (CTF) challenge by the Vacuumlabs Auditing team!

It is a game where Cardano developers and enthusiasts can try to exploit purposely vulnerable smart contracts and learn about the most common security issues and how to prevent them. In a way, you can try the job of auditors on some common Cardano vulnerabilities.

We believe this will provide the community with educational materials needed to write more secure smart contracts.

Tasks

0. hello_world — A sanity check to verify that everything's setup correctly.
1. sell_nft — Try to buy two NFTs by paying less than their stated prices!
2. vesting — Try to skip the vesting period.
3. multisig_treasury — Unlock treasury without all the signatures.
4. tipjar — Try to prevent others from tipping into a Tip Jar.
5. purchase_offer — Sell an NFT while collecting more money than offerred.
6. tipjar_v2 — The Tip Jar was patched. Try to prevent others from tipping into the upgraded Tip Jar.
7. multisig_treasury_v2 — The treasury was upgraded. Try to unlock it without all the signatures again.
8. lending — Hack a simple peer-to-peer lending protocol.
9. multisig_treasury_v3 — The treasury was upgraded again! Let's compromise it once again 💪.
10. king_of_cardano — Become the King of Cardano and prevent others from overthrowing you.

How it works

Each task has its own folder. It consists of three main parts:

• The validators written in Aiken. They are located in the validators folder. You can compile them by running aiken build in the root directory of the task.
• The off-chain code. We use the Lucid library and the Blockfrost API to interact with the Preview testnet. The off-chain scripts contain:
  • Code deploying the smart contracts onto the Cardano Preview testnet.
  • Sample interaction with the deployed contract. This is the part you should modify and / or extend to exploit a vulnerability.
  • Tests that verify if you successfully exploited the vulnerability or not.
• A README file containing task-specific instructions. The first sample hello_world task contains a bit more info on how exactly to play.

The tasks are more or less of an increasing difficulty. The suggested path is to go from a simple hello_world task up. The tasks' README's also explain more in the beginning, leaving more up to you in the more complex levels.

Setup

To be able to run the first task, just 3 steps of setup are needed:

1. Install Deno.
2. Install Aiken.
3. Copy the template config file in common/offchain/config_temp.ts to common/offchain/config.ts.

That's it and you can now play in the local Lucid emulator! The emulator is great for testing smart contracts fast.

You can now try the first hello_world task (read its README carefully) and get to the yellow test results.

Finishing the setup

To get to the green test results and really finish the task, it is required to finish it in the testnet environment. To set this up, there are a few more steps you need to take:

1. Generate a private key and address. We prepared a private key generation code for you, you can run it by:

   deno run --allow-net --allow-write ./common/offchain/generate_private_key.ts
   

   Put your private key into the PRIVATE_KEY constant located in the common/offchain/config.ts.

   DO NOT REUSE A PRIVATE KEY THAT YOU USE FOR MAINNET! Generate a new one instead!

2. Get Blockfrost API key by registering at https://blockfrost.io/ . Put this API key into the BLOCKFROST_API_KEY constant in the common/offchain/config.ts.

3. You need some starting ADA in your wallet so you can interact with the Cardano testnet. Request tADA into your address (see the newly created key.addr file) from the Cardano Faucet. The environment we use is Preview Testnet.

4. You are good to go! To verify that everything is set up correctly, try solving the very first sample task: Hello World. You should see green test results when everything is done correctly.

Troubleshooting

Videos

There are videos in the videos folder. Check them out if you're struggling with making the framework work. Beware, it can contain spoilers, especially the first video that solves the hello_world task entirely. The later videos do not explain the solutions. They are here mostly to demonstrate Catalyst milestones' completion. You should strive to find the solutions yourself.

Errors during a transaction submission

Sometimes, Lucid errors out when it submits a transaction. This usually happens on the real testnet when you wait for too short between two different transactions from your wallet.

In the meantime, if you encounter this error, you can try to change the default value of CONFIRMS_WAIT in the config to a higher number. This makes it wait for more confirmations before it follows up with the next transaction, increasing the time and making the chance of such errors smaller.

We have also encountered transactions in which Lucid wasn't able to determine the correct amount of ADA that needed to be placed into the UTxO, resulting in the transaction erroring out with Not enough ADA leftover to cover minADA, even if a sufficient amount of ADA was available. To address this issue, our transactions now deposit a fixed amount of at least 2 ADA into each UTxO.

Long waiting time on the testnet

From our experience, the time required for a transaction validation are ever changing on the preview testnet. If it takes too long, try to decrease the default value of CONFIRMS_WAIT in the config to a lower number. Be careful not to change it too low, otherwise you might get errors during submissions.

This is why we run the transactions on the Lucid emulator first. Only if they pass there we try to replicate it on the testnet as well.

Scoreboard

Successful solutions are recorded on the testnet. There is a script called scoreboard.ts that displays the number of successful solutions in a succinct way. You can run it using the command deno run --allow-net --allow-read scoreboard.ts.

Feedback

Join our Discord. You can ask questions, share your solutions and discuss anything (not only) security related. Alternatively, you can share your thoughts and feedback with us at audit@vacuumlabs.com as well.

Warning & Disclaimer

The smart contract code in the examples is purposely vulnerable. DO NOT copy parts of the code into your project, as you may copy a vulnerability, too. Beware that the code may contain more than a single vulnerability.

Changelog

This project is ever evolving. Please refer to the Changelog to see the changes over time.

License

Licensed under GPL-3.0. Full license text can be found here.