pytm

Threat Modeling with pytm

Overview

pytm is a Python library for programmatic threat modeling based on the STRIDE methodology. It enables security engineers to define system architecture as code, automatically generate data flow diagrams (DFDs), identify security threats across trust boundaries, and produce comprehensive threat reports. This approach integrates threat modeling into CI/CD pipelines, enabling shift-left security and continuous threat analysis.

Quick Start

Create a basic threat model:

#!/usr/bin/env python3
from pytm import TM, Server, Dataflow, Boundary, Actor

# Initialize threat model
tm = TM("Web Application Threat Model")
tm.description = "E-commerce web application"

# Define trust boundaries
internet = Boundary("Internet")
dmz = Boundary("DMZ")
internal = Boundary("Internal Network")

# Define actors and components
user = Actor("Customer")
user.inBoundary = internet

web = Server("Web Server")
web.inBoundary = dmz

db = Server("Database")
db.inBoundary = internal

# Define data flows
user_to_web = Dataflow(user, web, "HTTPS Request")
user_to_web.protocol = "HTTPS"
user_to_web.data = "credentials, payment info"
user_to_web.isEncrypted = True

web_to_db = Dataflow(web, db, "Database Query")
web_to_db.protocol = "SQL/TLS"
web_to_db.data = "user data, transactions"

# Generate threat report and diagram
tm.process()

Install pytm:

pip install pytm
# Also requires graphviz for diagram generation
brew install graphviz  # macOS
# or: apt-get install graphviz  # Linux

Core Workflows

Workflow 1: Create New Threat Model

Progress: [ ] 1. Define system scope and trust boundaries [ ] 2. Identify all actors (users, administrators, external systems) [ ] 3. Map system components (servers, databases, APIs, services) [ ] 4. Define data flows between components with security attributes [ ] 5. Run tm.process() to generate threats and DFD [ ] 6. Review STRIDE threats and add mitigations [ ] 7. Generate threat report with scripts/generate_report.py

Work through each step systematically. Check off completed items.

Workflow 2: STRIDE Threat Analysis

pytm automatically identifies threats based on STRIDE categories: