Mythril Symbolic Execution Skill

Deep vulnerability detection through symbolic execution using Mythril, a security analysis tool for EVM bytecode.

Capabilities

• Symbolic Execution: Configure and run symbolic execution analysis
• Transaction Depth Control: Set appropriate depth for complex interactions
• Trace Analysis: Interpret symbolic execution traces
• Integer Issues: Detect overflow/underflow paths (pre-0.8 Solidity)
• State Analysis: Find reentrancy via state change analysis
• Assertion Detection: Identify assertion failures and edge cases
• PoC Generation: Generate proof-of-concept exploit inputs

Installation

bash
# Install via pip
pip install mythril

# Or use Docker (recommended)
docker pull mythril/myth

# Verify installation
myth version

Basic Usage

Analyze Source Code

bash
# Analyze single file
myth analyze Contract.sol

# Analyze with Solidity version
myth analyze Contract.sol --solv 0.8.20

# Analyze specific contract
myth analyze Contract.sol:MyContract

Analyze Bytecode

bash
# Analyze deployed contract
myth analyze -a 0x<address> --rpc <rpc_url>

# Analyze bytecode file
myth analyze --bin-runtime contract.bin

Configuration Options

Transaction Depth

bash
# Default depth (2)
myth analyze Contract.sol

# Increased depth for complex interactions
myth analyze Contract.sol --execution-timeout 300 -t 3

# Deep analysis (slow)
myth analyze Contract.sol --execution-timeout 600 -t 4

Timeout Settings

bash
# Set execution timeout (seconds)
myth analyze Contract.sol --execution-timeout 300

# Set solver timeout
myth analyze Contract.sol --solver-timeout 10000

# Quick scan
myth analyze Contract.sol --execution-timeout 60 -t 2

Module Selection

bash
# Run specific modules
myth analyze Contract.sol --modules ether_thief,suicide

# Available modules
# - ether_thief
# - suicide
# - integer_overflow/underflow
# - delegatecall
# - arbitrary_write
# - state_change_external_call

Output Formats

Standard Output

bash
myth analyze Contract.sol

JSON Output

bash
myth analyze Contract.sol -o json > report.json

Markdown Output

bash
myth analyze Contract.sol -o markdown > report.md

JSONV2 (Detailed)

bash
myth analyze Contract.sol -o jsonv2 > detailed.json

Vulnerability Detection

Reentrancy Detection

Mythril detects reentrancy by tracking:

• External calls
• State changes after calls
• ETH transfers

==== External Call To User-Supplied Address ====
SWC ID: 107
Severity: Low
Contract: Vulnerable
Function name: withdraw()
PC address: 1234
Estimated Gas Usage: 2500 - 10000
Type: Informational
...

Integer Overflow/Underflow

==== Integer Overflow ====
SWC ID: 101
Severity: High
Contract: Token
Function name: transfer(address,uint256)
PC address: 567
Estimated Gas Usage: 3000 - 5000
A possible integer overflow exists in the function...

Unprotected Self-Destruct

==== Unprotected Selfdestruct ====
SWC ID: 106
Severity: High
Contract: Vulnerable
Function name: kill()
Any sender can trigger self-destruction...

Advanced Usage

Concolic Execution

bash
# Use concrete values where possible
myth analyze Contract.sol --strategy dfs --execution-timeout 300

Custom Constraints

bash
# Analyze with constraints file
myth analyze Contract.sol --constraints constraints.json

State Space Pruning

bash
# Limit state explosion
myth analyze Contract.sol --max-depth 30 --call-depth-limit 3

CI/CD Integration

GitHub Actions

yaml
name: Mythril Analysis
on: [push]

jobs:
  mythril:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Run Mythril
        uses: docker://mythril/myth
        with:
          args: analyze /github/workspace/contracts/*.sol --solv 0.8.20

Custom Script

bash
#!/bin/bash
for file in contracts/*.sol; do
    myth analyze "$file" --solv 0.8.20 -o json > "reports/$(basename $file .sol).json"
done

Interpreting Results

Severity Levels

| Level | Description | Action | |-------|-------------|--------| | High | Critical vulnerability | Fix immediately | | Medium | Potential issue | Investigate | | Low | Minor concern | Consider fixing | | Informational | Code quality | Optional fix |

SWC Registry

| SWC ID | Name | Description | |--------|------|-------------| | SWC-101 | Integer Overflow | Arithmetic overflow | | SWC-104 | Unchecked Return | Ignored return values | | SWC-106 | Unprotected Destruct | Accessible selfdestruct | | SWC-107 | Reentrancy | State change after call | | SWC-110 | Assert Violation | Reachable assertion | | SWC-116 | Timestamp Dependence | Block timestamp usage |

Process Integration

| Process | Purpose | |---------|---------| | smart-contract-security-audit.js | Deep vulnerability analysis | | smart-contract-fuzzing.js | Complement to fuzzing | | invariant-testing.js | Property verification |

Comparison with Other Tools

| Tool | Technique | Speed | Depth | |------|-----------|-------|-------| | Mythril | Symbolic Execution | Slow | Deep | | Slither | Static Analysis | Fast | Surface | | Echidna | Fuzzing | Medium | Medium | | Certora | Formal Verification | Slow | Deepest |

Best Practices

1. Start with quick scans, increase depth as needed
2. Use Docker for consistent environment
3. Run on CI for automated security checks
4. Combine with static analysis (Slither)
5. Verify findings manually before reporting
6. Use appropriate Solidity version flag

Troubleshooting

Out of Memory

bash
# Increase timeout, reduce depth
myth analyze Contract.sol --execution-timeout 600 -t 2

Solver Timeout

bash
# Increase solver timeout
myth analyze Contract.sol --solver-timeout 30000

Compilation Errors

bash
# Specify Solidity version
myth analyze Contract.sol --solv 0.8.20

# Use specific compiler
myth analyze Contract.sol --solc-json solc.json

See Also

• skills/slither-analysis/SKILL.md - Static analysis
• skills/echidna-fuzzer/SKILL.md - Property-based fuzzing
• agents/solidity-auditor/AGENT.md - Security auditor
• Mythril Documentation