Confusum Contractum: Confused Deputy Vulnerabilities in Ethereum Smart Contracts

This repository contains the code used for our USENIX paper Confusum Contractum: Confused Deputy Vulnerabilities in Ethereum Smart Contracts. Our system, Jackal, can be used to find exploitable confused deputy vulnerabilities on the Ethereum blockchain.

⚠️ Disclaimers

• For different technical and ethical reasons, we are not releasing a fully automated "push-one-button" solution for the identification and automatic exploitation of smart contracts. Rather, we open-sourced all the necessary scripts to demonstrate the analyses presented in the paper. Interested researchers will have all the necessary code to replicate our work. In case something does not click, please reach out to us :)

• ALL the high-profile vulnerable contracts discovered with Jackal have already been reported to the CISA. The rest of the contracts do not hold any digital currency at the time of writing. That being said, we take an extra precautionary step and avoid sharing the list of vulnerable addresses publicly. If this is important for your research please reach out to us with a valid academic endorsement and we can share the dataset.

• It is YOUR responsibility to report any new vulnerability discovered using our methodology/new methodologies based on Jackal.

⚡️ Setup

Just clone the repo and run the setup.sh script:

$ git clone https://github.com/ucsb-seclab/jackal.git && source ./setup.sh

This will install ethpwn (the Swiss Army Knife for Smart Contracts Hacking) and greed, our symbolic execution engine for EVM smart contracts.

The script will ask for a WEB3_RPC_ENDPOINT URL to a JSON-RPC Web3 endpoint. If you are running a private node this can be, e.g., http://0.0.0.0:8545. Otherwise, you can use services like Infura or Alchemy to obtain access to their API (there is a free-tier which is more than enough for using our tool).

Note: Using an Infura/Alchemy node will result in slower performances when running the GenericChecker and the TokenChecker. We suggest running a private Web3 endpoint such as Erigon or Geth.

🚀 Usage

CALL Inspector

The identification of controllable CALL(s) in a smart contract binary is done with the script run.py in CheckConfusedContracts. e.g.,:

$ cd jackal/CheckConfusedContracts
$ python run.py --ca <CONTRACT_ADDR_CHECKSUMMED> --block 16380000 

<CONTRACT_ADDR_CHECKSUMMED> is the address of the contract you want to analyze, while 16380000 is the block (height) that is gonna be used as a reference for this analysis. If a controllable CALL is detected the script will report a True positive by highlighting the log with a green color.

Generic Checker

This script is used to find possible "generic" targets (see Section 4.3 in the paper) for an end-to-end exploitation of a confused deputy vulnerability. Please read the note in the generic_checker.py for more information. Usage:

$ cd jackal/FindContractTargets/GenericChecker
$ python generic_checker.py --confused <CONFUSED_CONTRACT_ADDR_CHECKSUMMED> --target 0xdAC17F958D2ee523a2206206994597C13D831ec7 --tx 0x15bef4b45379ad3dfa676f206c1ce0d9d4a18164d82a0d1a71737652c9456212 --func 0xa9059cbb

Token Checker

This script is used to find possible ERC20 targets (see Section 4.3 in the paper) for an end-to-end exploitation of a confused deputy vulnerability. Please read the note in the tokens_checker.py for more information. Usage:

$ cd jackal/FindContractTargets/TokenChecker
$ python tokens_checker.py --ca <CONFUSED_CONTRACT_ADDR_CHECKSUMMED> --block-start 14104827

Automatic Exploit Generation

Finally, this script implement the (A)utomatic (E)xploit (G)eneration algorithm described in Section 4.4 of the paper. Specifically, this script automatically synthetize the necessary CALLDATA to (1) force a confused contract to call a transfer function in an ERC20 contract of choice, and (2) gracefully terminate the execution to complete the exploit. Please read the note in the aeg.py script for further information. Usage:

$ cd jackal/ERC20AutomaticExploitGeneration
$ python aeg.py <CONFUSED_CONTRACT_ADDR_CHECKSUMMED> --aa_call_id 0x9f7 --contract_target 0x6B175474E89094C44Da98b954EedeAC495271d0F --function_target_sig 0xa9059cbb --block 11469710 --entry_point 0xcbd8c06a

..from great power comes great responsibility