Fuzzing
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Fuzzing 1-2-3
How to get from zero to fuzzing hero πŸ’ͺ
There are going to be three main steps to set up fuzzing:
1. Write properties using Scribble​
2. Deploy annotated contracts to a local Ethereum node
3. Start a fuzzing campaign!

Writing Properties

The first step is where you’ll be using Scribble to write properties that the fuzzer should check. Without such custom properties, fuzzing can only find generic vulnerabilities and assertion violations.
Interested in vulnerability detection? Check out our other product, MythX. It uses fuzzing, symbolic execution and static analysis to detect tons of different vulnerabilities out of the box.
There are tons of ways that you can write properties and property checks. We recommend Scribble! It was designed from the ground up to work well for fuzzing and property based testing!
You can find the Scribble documentation here.
You can learn everything you need about writing properties here:

Seed Deployments

In the second step, you’ll deploy Scribble-instrumented smart contracts to a local Ethereum node. Why? We will copy over this deployment into our fuzzer and use it as a seed to initialize our fuzzing campaign. This way, fuzzing starts on an actual deployment of the components in your system, and we’re able to test how the system components interact.
πŸ’‘ You can often repurpose existing test fixtures or deployment scripts for creating your fuzzing seeds!
Browse over to the following page for more information about how to set up seed deployments:

Fuzzing

The last step is where the fun is at! We’ll start fuzzing!
We first build a simple configuration that tells our CLI (see the installation instructions to get started) where to find all the artifacts that should be fuzzed.
# .fuzz_token.yml
​
analyze:
# We need to know where the dependencies live
remappings:
- "@openzeppelin=./node_modules/@openzeppelin"
fuzz:
# Tell the CLI where to find the compiled contracts and compilation artifacts
build_directory: artifacts
# The following address is going to be the main target for the fuzzing campaign
deployed_contract_address: "0x48b8050b4174f7871ce53AaF76BEAcA765037BFf"
# We'll do fuzzing with 4 cores πŸš€
number_of_cores: 4
# When the campaign is created it'll get a name <prefix>_<random_characters>
campaign_name_prefix: "my-first-campaign"
# Enable the following option if you're fuzzing Scribble-annotated code.
# It will visualise all the results for the original source code,
# instead of the instrumentation code.
map_to_original_source: true
# Point to your Ethereum node which holds the seed deployment 🌱
rpc_url: "http://localhost:8545"
# This is the contract that the campaign will show coverage for, map issues to, etc.
# It's a list of all the relevant contracts (don't worry about dependencies, we'll get those automatically πŸ™Œ)
targets:
- "contracts/Token.sol"
You only need to setup your configuration once! Then you're all set to fuzz in seconds!
Want to learn more about the configuration options?
You can now start a fuzzing campaign!
$ fuzz -c .fuzz_token.yml run
​
You can find your report at: <report_url>
Let's hope we don't find any bugs in your contracts! 🀞
For more information on the campaign reports check out this page:
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On this page
Writing Properties
Seed Deployments
Fuzzing