Mythril

Mythril is a security analysis tool for Ethereum smart contracts. It uses the LASER-ethereum symbolic virtual machine to detect various types of issues. Use it to analyze source code or as a nmap-style black-box blockchain scanner (an "ethermap" if you will).

Installation and setup

Install from Pypi:

$ pip3 install mythril

Or, clone the GitHub repo to install the newest master branch:

$ git clone https://github.com/b-mueller/mythril/
$ cd mythril
$ python3 setup.py install

Note that Mythril requires Python 3.5 to work.

Security analysis

Run myth -x with one of the input options described below to run the analysis. This will run the Python modules in the /analysis/modules directory.

Mythril detects a range of security issues, including integer underflows, owner-overwrite-to-Ether-withdrawal, and others. However, the analysis will not detect business logic issues and is not equivalent to formal verification.

Analyzing Solidity code

In order to work with Solidity source code files, the solc command line compiler needs to be installed and in path. You can then provide the source file(s) as positional arguments, e.g.:

$ myth -x solidity_examples/ether_send.sol 
==== Ether send ====
Type: Warning
Contract: Crowdfunding
Function name: withdrawfunds()
PC address: 816
In the function 'withdrawfunds()' a non-zero amount of Ether is sent to msg.sender.

There is a check on storage index 7. This storage slot can be written to by calling the function 'crowdfunding()'.
--------------------
In file: solidity_examples/ether_send.sol:18

msg.sender.transfer(this.balance)

If an input file contains multiple contract definitions, Mythril analyzes the last bytecode output produced by solc. You can override this by specifying the contract name explicitly:

$ myth -x OmiseGo.sol:OMGToken

Specifying Solc versions

You can specify a version of the solidity compiler to be used with --solv <version number>. Please be aware that this uses py-solc and will only work on Linux and OS X versions of Mavericks, Yosemite and El Capitan as of the time of this writing. It will check you locally installed compiler, if this is not what is specified, it will download binaries on Linux or try to compile from source on OS X.

Output formats

By default, analysis results are printed to the terminal in text format. You can change the output format with the -o argument:

$ myth -xo json underflow.sol

The json format is useful for integration into other tools, while -o markdown creates a human-readable report.

Analyzing a Truffle project

Truffle Suite is a popular development framework for Ethereum. To analyze the smart contracts in a Truffle project, change in the project root directory and make run truffle compile followed by myth --truffle.

Working with contracts on the mainnet and testnets

When analyzing contracts on the blockchain, Mythril will by default query a local node via IPC. If you want to analyze contracts on the live Ethereum network, you can also use the built-in INFURA support. Alternatively, you can override the RPC settings with the --rpc argument.

To analyze a contract on the mainnet, run:

$ myth --infura-mainnet -x -a 0x5c436ff914c458983414019195e0f4ecbef9e6dd

Adding the -l flag will cause Mythril to automatically retrieve dependencies, such as dynamically linked library contracts:

$ myth --infura-mainnet -x -a 0xEbFD99838cb0c132016B9E117563CB41f2B02264 -l -v1

Speed vs. Coverage

The maximum recursion depth for the symbolic execution engine can be controlled with the --max-depth argument. The default value is 12. Lowering this value reduces the analysis time as well as the coverage / number of explored states.

$ myth --infura-mainnet -x -a 0x5c436ff914c458983414019195e0f4ecbef9e6dd --max-depth 8

Control flow graph

The -g FILENAME option generates an interactive jsViz graph:

$ myth --infura-mainnet -g ./graph.html -a 0x5c436ff914c458983414019195e0f4ecbef9e6dd --max-depth 8

The "bounce" effect, while awesome (and thus enabled by default), sometimes messes up the graph layout. Try adding the --enable-physics flag for a very entertaining "bounce" effect that unfortunately completely destroys usability.

Blockchain exploration

If you are planning to do batch operations or use the contract search features, running a go-ethereum node is recommended. Start your local node as follows:

$ geth --syncmode fast

Mythril builds its own contract database to enable fast search operations. This enables operations like those described in the legendary "Mitch Brenner" blog post in seconds minutes instead of days. Unfortunately, the initial sync process is slow. You don't need to sync the whole blockchain right away though: If you abort the syncing process with ctrl+c, it will be auto-resumed the next time you run the --init-db command.

$ myth --init-db
Starting synchronization from latest block: 4323706
Processing block 4323000, 3 individual contracts in database
(...)

The default behavior is to only sync contracts with a non-zero balance. You can disable this behavior with the --sync-all flag, but be aware that this will result in a huge (as in: dozens of GB) database.

Searching from the command line

The search feature allows you to find contract instances that contain specific function calls and opcode sequences. It supports simple boolean expressions, such as:

$ myth --search "func#changeMultisig(address)#"
$ myth --search "code#PUSH1 0x50,POP#"
$ myth --search "func#changeMultisig(address)# and code#PUSH1 0x50#"

Reading contract storage

You can read the contents of storage slots from a deployed contract as follows.

$ myth --storage 0,1 -a "0x76799f77587738bfeef09452df215b63d2cfb08a"
0x0000000000000000000000000000000000000000000000000000000000000003

Utilities

Disassembler

Use the -d flag to disassemble code. The disassembler accepts a bytecode string or a contract address as its input.

$ myth -d -c "0x6060"
0 PUSH1 0x60

Specifying an address via -a ADDRESS will download the contract code from your node.

$ myth -d -a "0x2a0c0dbecc7e4d658f48e01e3fa353f44050c208"
0 PUSH1 0x60
2 PUSH1 0x40
4 MSTORE
(...)
1135 - FUNCTION safeAdd(uint256,uint256) -
1136 CALLVALUE
1137 ISZERO

Finding cross-references

It is often useful to find other contracts referenced by a particular contract. E.g.:

$ myth --search "code#DELEGATECALL#"
Matched contract with code hash 07459966443977122e639cbf7804c446
Address: 0x76799f77587738bfeef09452df215b63d2cfb08a, balance: 1000000000000000
$ myth --xrefs -a 0x76799f77587738bfeef09452df215b63d2cfb08a
5b9e8728e316bbeb692d22daaab74f6cbf2c4691

Calculating function hashes

To print the Keccak hash for a given function signature:

$ myth --hash "setOwner(address)"
0x13af4035

Function signatures

Whenever you disassemble or analyze binary code, Mythril will try to resolve function names using its local signature database. The database must be provided at ~/.mythril/signatures.json. You can start out with the default file as follows:

$ mkdir ~/.mythril
$ cd ~/.mythril
$ wget https://raw.githubusercontent.com/b-mueller/mythril/master/signatures.json

When you analyze Solidity code, new function signatures are added to the database automatically.

Credit

• JSON RPC library is adapted from ethjsonrpc (it doesn't seem to be maintained anymore, and I needed to make some changes to it).

• The signature data in signatures.json was initially obtained from the Ethereum Function Signature Database.

• Many features, bugfixes and analysis modules have been added by contributors.