Security Anti-Patterns Guard for Python

Overview

Code generation guard that prevents security vulnerabilities while writing Python web application code. Covers OWASP Top 10 Web (2021), OWASP API Security Top 10 (2023), with CWE references throughout.

Stack: Python, Django, Flask, FastAPI, SQLAlchemy, Pydantic

When to Activate

Activate when generating code that:

• Handles user input (forms, API requests, file uploads)
• Queries databases (SQL, ORM operations)
• Performs authentication or authorization
• Manages sessions or tokens
• Processes files or paths
• Serializes/deserializes data
• Uses cryptographic operations
• Executes system commands

Critical Rules (Top 10)

1. NEVER use f-strings or .format() in SQL queries – use parameterized queries or ORM
2. NEVER use pickle.loads() on untrusted data – use JSON with schema validation
3. NEVER use eval(), exec(), or compile() on user input
4. NEVER use os.system() or shell=True with user data – use subprocess.run() with list args
5. NEVER use yaml.load() – use yaml.safe_load()
6. NEVER hardcode secrets – use environment variables
7. NEVER use random for security – use secrets module
8. NEVER use md5 or sha1 for passwords – use bcrypt or argon2
9. NEVER trust user-supplied file paths – validate with pathlib and check resolved path
10. NEVER skip authorization checks – always verify user owns/can access the resource

Module Index

Quick Decision Tree

User input involved?
├─ Database query → See references/injection.md (use ORM/parameterized)
├─ File path → See references/file-operations.md (use pathlib + resolve check)
├─ Command execution → See references/injection.md (subprocess with list args)
├─ Deserialization → See references/deserialization.md (NEVER pickle untrusted)
├─ Template rendering → See references/xss-output.md (auto-escape enabled)
└─ API endpoint → See references/auth-access.md + references/input-validation.md

Storing/generating secrets?
├─ API keys → See references/crypto-secrets.md (env vars)
├─ Passwords → See references/crypto-secrets.md (bcrypt/argon2)
└─ Tokens → See references/crypto-secrets.md (secrets module)

Framework-specific?
├─ Django → See references/django-security.md
├─ FastAPI → See references/fastapi-flask.md
└─ Flask → See references/fastapi-flask.md

How to Use This Skill

1. During code generation: Reference relevant module for specific vulnerability patterns
2. Code review: Check generated code against patterns in each module
3. When uncertain: Default to the more secure option; add explicit comments explaining security decisions

Sources

• OWASP Python Security Cheat Sheet
• Django Security Documentation
• FastAPI Security Tutorial
• Bandit – Python Security Linter
• PEP 506 – secrets module