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Obsolete, not maintained anymore, don't install it, don't use it, you were warned!

License: MIT CircleCI Codacy Badge PyPI Code style: black Maintainability Rating

A monitor for smart contracts that checks for security vulnerabilities.

Karl Vreski

Video presentation

DefCon 27


Get latest version of Karl.

$ pip install --user karl

Install Ganache with npm if you want Karl to test the found vulnerabilities in a sandbox (--sandbox=true, disabled by default), to reduce false positives.

$ npm i -g ganache-cli


Karl will allow you to monitor a blockchain for vulnerable smart contracts that are being deployed.

It connects to the blockchain, monitors for new blocks and runs mythril for every new smart contract deployed.

The output can be displayed in the console, saved in files in a folder or POSTed to a URL.

Output can be:

  • stdout just posting the results to standard output
  • folder create a file for each vulnerable contract in a folder
  • posturl POST the results to an http endpoint

Help message

$ karl --help
usage: karl [-h] [--rpc] [--rpc-tls RPC_TLS] [--block NUMBER] [--output Can be one of: stdout, posturl, folder]
            [--posturl POSTURL] [--folder-output FOLDER_OUTPUT] [--sandbox SANDBOX] [--timeout SECONDS] [--loop-bound LOOP_BOUND] [--tx-count NUMBER]
            [--modules [MODULES [MODULES ...]]] [--onchain-storage ONCHAIN_STORAGE] [--verbose] [--version]

Smart contract monitor using Mythril to find exploits

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit

RPC options:
                        Custom RPC settings (default: None)
  --rpc-tls RPC_TLS     RPC connection over TLS (default: False)
  --block NUMBER        Start from this block, otherwise start from latest (default: None)

  --output Can be one of: stdout, posturl, folder
                        Where to send results (default: stdout)
  --posturl POSTURL     Send results to a RESTful url [when using `--output posturl`] (default: None)
  --folder-output FOLDER_OUTPUT
                        Save files to this folder [when using `--output folder`] (default: None)

  --sandbox SANDBOX     Test found transactions in a Ganache sandbox (default: False)

Scan options:
  --timeout SECONDS     Scan timeout per contract (default: 600)
  --loop-bound LOOP_BOUND
                        Maximum number of loop iterations (default: 3)
  --tx-count NUMBER     Maximum number of transactions (default: 3)
  --modules [MODULES [MODULES ...]]
                        Modules to use for scanning (default: ['ether_thief', 'suicide'])
  --onchain-storage ONCHAIN_STORAGE
                        Whether onchain access should be done or not (default: True)

  --verbose, -v         Set verbose (default: 4)


Running against the mainnet

$ karl --rpc
Stdout initialized
Scraping block 6745471
Scraping block 6745472
Scraping block 6745473
Analyzing 0xf8c065bB1DafC99eE5476a2b675FAC4a036a4B07
Scraping block 6745474
Analyzing 0xC9e044D76f211E84bA651b30BBA86758ca8017c7
Scraping block 6745475
Scraping block 6745476
Scraping block 6745477
Analyzing 0x19427b8FD32dfEc78393517Da416bC5C583E6065

Running against ganache with stdout enabled

$ karl --rpc http://localhost:8545 --output=stdout
INFO:mythril.mythril:Using RPC settings: ('localhost', 8545, False)
INFO:mythril.analysis.modules.suicide:Suicide module: Analyzing suicide instruction
Initial balance = 100000000000000000000, final balance = 100999999999999985722

Type = VulnerabilityType.KILL_AND_WITHDRAW
Description = Looks line anyone can kill this contract and steal its balance.
Transactions = [{'from': '0x1dF62f291b2E969fB0849d99D9Ce41e2F137006e', 'to': '0x2F2B2FE9C08d39b1F1C22940a9850e2851F40f99', 'data': '0xcbf0b0c0bebebebebebebebebebebebe1dF62f291b2E969fB0849d99D9Ce41e2F137006e', 'value': 0}]

Running against ganache with posturl enabled

$ karl --rpc [ganache](http://localhost:8545) --output=posturl --posturl=http://localhost:8080
Posturl initialized
Scraping block 5
Analyzing 0x4b8e80acaE3F0db32e5d35925EfaA97D477dBb70

And it will send this to the listening service

$ nc -l 8080
Accept-Encoding: identity
Content-Type: application/x-www-form-urlencoded
Content-Length: 725
Host: localhost:8080
User-Agent: Python-urllib/3.7
Connection: close

    "error": null,
    "issues": [{
        "address": 722,
        "contract": "0x4b8e80acaE3F0db32e5d35925EfaA97D477dBb70",
        "debug": "Transaction Sequence: {'1': {'calldata': '0x56885cd8', 'call_value': '0x0', 'caller': '0xaaaaaaaabbbbbbbbbcccccccddddddddeeeeeeee'}, '4': {'calldata': '0x6c343ffe', 'call_value': '0x0', 'caller': '0xaaaaaaaabbbbbbbbbcccccccddddddddeeeeeeee'}}",
        "description": "Arbitrary senders other than the contract creator can withdraw ETH from the contract account without previously having sent an equivalent amount of ETH to it. This is likely to be a vulnerability.",
        "function": "withdrawfunds()",
        "max_gas_used": 1749,
        "min_gas_used": 1138,
        "swc-id": "105",
        "title": "Ether thief",
        "type": "Warning"
    "success": true

Running against the mainnet with folder output enabled

$ karl --rpc karl --rpc --output folder


Running locally with a specially crafted vulnerable contract:


Running on the main net using Infura:




If you get this error

  #include <openssl/aes.h>
compilation terminated.
error: command 'x86_64-linux-gnu-gcc' failed with exit status 1

You must install the openssl source code libraries


$ sudo apt-get install libssl-dev


This tool is inspired by Bernhard's initial prototyping and it heavily uses his project Myth.