malwi-box 0.0.4

Intercept, audit, and block critical Python operations at runtime

malwi-box

Intercept, audit, and block critical Python operations at runtime.

Shipped without any dependencies, except pip

Use Cases

• 🔬 Malware analysis - Safely detonate suspicious Python code and observe its behavior
• 📦 Dependency auditing - Discover what file, network, and process access a package actually needs
• 🔒 Runtime protection - Enforce allowlists to block unauthorized operations in production

Warning: This tool is not executed in isolation or virtualization, it runs on your actual machine, kernel and CPU. Use it at your own risk. Still it allows to reduce the blast radius of typical Python malware.

Installation

pip install malwi-box

Or with uv:

uv tool install malwi-box

Quick Start

# Block file access
$ malwi-box eval "open('/etc/passwd').read()"
[malwi-box] Blocked: Read file: /etc/passwd

# Block network requests
$ malwi-box eval "import urllib.request; urllib.request.urlopen('https://evil.com')"
[malwi-box] Blocked: DNS lookup: evil.com

# Block shell commands
$ malwi-box eval "import os; os.system('whoami')"
[malwi-box] Blocked: Shell command: /bin/sh -c whoami

# Block subprocess execution
$ malwi-box eval "import subprocess; subprocess.run(['curl', 'https://evil.com'])"
[malwi-box] Blocked: Execute: /usr/bin/curl

# Log suspicious encoding (info-only, not blocked)
$ malwi-box eval "import base64; base64.b64encode(b'secret')"
[malwi-box] Base64: b64encode

Commands

run

Run a Python script or module with sandboxing.

malwi-box run script.py [args...]
malwi-box run --force script.py     # log violations without blocking
malwi-box run --review script.py    # approve/deny each operation

eval

Execute a Python code string with sandboxing.

malwi-box eval "print('hello')"
malwi-box eval --force "import os; os.system('id')"
malwi-box eval --review "open('/etc/passwd').read()"

install

Install pip packages with sandboxing. Most malware packages perform malicious activities at install-time.

malwi-box install package
malwi-box install package --version 1.2.3
malwi-box install -r requirements.txt
malwi-box install --review package # approve/deny each operation

config

Manage configuration.

malwi-box config create # creates .malwi-box.toml
malwi-box config create --path FILE

Configuration Reference

Config file: .malwi-box.toml

# File access permissions
allow_read = [
  "$PWD",                     # working directory
  "$PYTHON_STDLIB",           # Python standard library
  "$PYTHON_SITE_PACKAGES",    # installed packages
  "$HOME/.config/myapp",      # specific config directory
  "/etc/hosts",               # specific file
]

allow_create = [
  "$PWD",                     # allow creating files in workdir
  "$TMPDIR",                  # allow temp files
]

allow_modify = [
  "$PWD/data",                # only modify files in data/
  { path = "/etc/myapp.conf", hash = "sha256:abc123..." },
]

allow_delete = []             # no deletions allowed

# Network permissions
allow_domains = [
  "pypi.org",                 # allow any port
  "files.pythonhosted.org",
  "api.example.com:443",      # restrict to specific port
]

allow_ips = [
  "10.0.0.0/8",               # CIDR notation
  "192.168.1.100:8080",       # specific IP:port
  "[::1]:443",                # IPv6 with port
]

# HTTP URL path restrictions (optional, empty = domain-only mode)
allow_http_urls = [
  "api.example.com/v1/*",         # glob pattern for paths
  "cdn.example.com/assets/*",
  "https://secure.example.com/*", # explicit scheme
]

# HTTP methods allowed (optional, empty = all methods)
allow_http_methods = ["GET", "POST", "HEAD"]

# Raw socket access (default: false, blocks SOCK_RAW creation)
allow_raw_sockets = false

# Process execution
allow_executables = [
  "/usr/bin/git",             # allow by path
  "$PWD/.venv/bin/*",         # glob pattern
  { path = "/usr/bin/curl", hash = "sha256:abc123..." },
]

allow_shell_commands = [
  "/usr/bin/git *",           # glob pattern matching
  "/usr/bin/curl *",
]

# Environment variables
allow_env_var_reads = []      # restrict env access
allow_env_var_writes = ["PATH", "PYTHONPATH"]

Path Variables

Variable	Description
$PWD	Working directory
$HOME	User home directory
$TMPDIR	System temp directory (macOS: /var/folders/.../T, Linux: /tmp)
$CACHE_HOME	User cache directory (macOS: ~/Library/Caches, Linux: ~/.cache)
$PIP_CACHE	pip cache directory
$VENV	Active virtualenv root (if $VIRTUAL_ENV is set)
$PYTHON_STDLIB	Python standard library
$PYTHON_SITE_PACKAGES	Installed packages (purelib)
$PYTHON_PLATLIB	Platform-specific packages
$PYTHON_PREFIX	Python installation prefix
$ENV{VAR}	Any environment variable

Sensitive Paths (Always Blocked)

The following paths are automatically blocked even if they match an allow rule:

• SSH keys and GPG (~/.ssh, ~/.gnupg)
• Cloud credentials (~/.aws, ~/.azure, ~/.config/gcloud, ~/.kube)
• Browser data (Chrome, Firefox, Safari, Edge)
• Password managers (1Password, Bitwarden, KeePassXC, keychains)
• Development secrets (~/.npmrc, ~/.pypirc, ~/.netrc, ~/.git-credentials)
• System secrets (/etc/shadow, /etc/sudoers, /etc/ssh/*_key)

Network Behavior

• Domains in allow_domains automatically permit their resolved IPs
• Direct IP access requires explicit allow_ips entries
• CIDR notation supported for IP ranges
• Port restrictions supported for both domains and IPs

HTTP URL Path Allowlisting

• If allow_http_urls is empty, only domain-level checks apply (default behavior)
• If allow_http_urls is configured, requests must match both domain AND URL pattern
• Scheme (http://, https://) is optional in patterns - omit to match both
• Glob patterns supported for paths: api.example.com/v1/*
• Subdomain matching: example.com/api/* matches api.example.com/api/*

HTTP Method Restrictions

• If allow_http_methods is empty, all HTTP methods are allowed
• If configured, only listed methods are permitted (e.g., ["GET", "HEAD"])

HTTP Library Coverage

HTTP request interception covers:

• urllib.request (stdlib)
• http.client (stdlib)
• urllib3
• requests
• httpx
• aiohttp

Bypass note: Raw socket HTTP requests bypass library hooks but are blocked by default (allow_raw_sockets = false). The socket.connect event still captures all connections at the network level.

Hash Verification

Executables and files can include SHA256 hashes:

allow_executables = [
  { path = "/usr/bin/git", hash = "sha256:e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855" },
]

How It Works

Uses Python's PEP 578 audit hooks via a C++ extension to intercept:

• File operations (open)
• Network requests (socket.connect, socket.getaddrinfo)
• HTTP requests (urllib.Request + profile hooks for requests, httpx, urllib3, aiohttp, http.client)
• Process execution (subprocess.Popen, os.exec*, os.system)
• Library loading (ctypes.dlopen)
• Raw socket creation (socket.__new__ with SOCK_RAW)

Protections against bypass:

• Blocks sys.addaudithook to prevent registering competing hooks
• Blocks sys.settrace and sys.setprofile to prevent debugger-based evasion
• Blocks ctypes.dlopen by default to prevent loading native code that bypasses hooks

Blocked operations terminate immediately with exit code 78.

Info-Only Events

Some operations are logged for security awareness but never blocked. They help identify potentially suspicious behavior during malware analysis:

Event	Description	Example Output
encoding.base64	Base64 encoding/decoding	Base64: b64encode
crypto.cipher	Cipher encryption/decryption (cryptography library)	Cipher: Encrypt
crypto.fernet	Fernet encryption/decryption	Fernet: encrypt

These events are always logged regardless of mode (run, force, or review) and cannot be disabled. They help identify:

• Data exfiltration attempts (base64 encoding)
• Ransomware behavior (encryption operations)
• Obfuscation techniques

Limitations

• Audit hooks cannot be bypassed from Python, but native code can
• Here it is important to review which executables are allow-listed