Mythril

Mythril is an assembler and disassembler for Ethereum VM bytecode. It was created for low-level testing/fuzzing of EVM implementations.

Installation

Clone the git repo:

$ git clone https://github.com/b-mueller/mythril/
$ pip install -r requirements.txt

Usage

To disassemble a piece of bytecode, pass it on the command line:

$ ./mythril.py -d -c "0x606060405050"
PUSH1 0x60
PUSH1 0x40
POP
POP

Modifying and re-assembling code

Mythril can assemble code from input files that contain one instruction per line. To start from an existing contract, save the disassembly to a text file:

$ ./mythril.py -d -c "0x606060405050" -o code.easm

Edit the instructions in a text editor. For example, we can change the two PUSH instruction from the original example:

PUSH2 0x4050
PUSH4 0x60708090
POP
POP

Save the file and run Mythril with the -a flag to re-assemble:

$ ./mythril.py -a code.easm 
0x61405063607080905050

The virtual machine language is described in the Ethereum Yellowpaper.

Loading a contract from the Ethereum blockchain

You can also load code from an existing contract in the Ethereum blockchain. For this, you need to have a full node running, and the RPC debug interface must be activated. For example, when running geth you can do this as follows:

$ geth --syncmode full --rpc --rpcapi eth,debug

To load contract code from your node, pass the TxID of the transaction that created the contract:

./mythril.py -d -t 0xbf7518b40ab1242af74229512592f77736569157faffbf373cc1b4f5d499b967

Note: If you want to get code from the Ethereum mainnet, it is easier to download it from Etherscan.