nyx/docs/rules/python.md

Python Rules

Nyx detects Python vulnerabilities through AST patterns and taint analysis, covering code execution, command injection, deserialization, SQL injection, and weak crypto.

Taint Labels

Python has moderate taint label coverage. Sources, sinks, and sanitizers are defined in src/labels/python.rs.

Sources

Matcher	Cap
os.getenv, os.environ	all
request.args, request.form, request.json, request.headers, request.cookies, input	all
sys.argv	all
argparse.parse_args, urllib.request.urlopen, requests.get, requests.post	all

Sanitizers

Matcher	Cap
html.escape	HTML_ESCAPE
shlex.quote	SHELL_ESCAPE
os.path.realpath	FILE_IO

Sinks

Matcher	Cap
eval, exec	SHELL_ESCAPE
os.system, os.popen, subprocess.call, subprocess.run, subprocess.Popen, subprocess.check_output, subprocess.check_call	SHELL_ESCAPE
cursor.execute, cursor.executemany	SHELL_ESCAPE
send_file, send_from_directory	FILE_IO
open	FILE_IO

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AST Pattern Rules

Code Execution

Rule ID	Severity	Tier	Description
py.code_exec.eval	High	A	eval() — dynamic code execution
py.code_exec.exec	High	A	exec() — dynamic code execution
py.code_exec.compile	Medium	A	compile() with exec/eval mode

Command Execution

Rule ID	Severity	Tier	Description
py.cmdi.os_system	High	A	os.system() — shell command execution
py.cmdi.os_popen	High	A	os.popen() — shell command execution
py.cmdi.subprocess_shell	High	B	subprocess.* with shell=True

Deserialization

Rule ID	Severity	Tier	Description
py.deser.pickle_loads	High	A	pickle.loads() / pickle.load() — arbitrary object deserialization
py.deser.yaml_load	High	A	yaml.load() without SafeLoader
py.deser.shelve_open	Medium	A	shelve.open() — pickle-backed deserialization

SQL Injection

Rule ID	Severity	Tier	Description
py.sqli.execute_format	Medium	B	cursor.execute() with string concatenation

Weak Crypto

Rule ID	Severity	Tier	Description
py.crypto.md5	Low	A	hashlib.md5() — weak hash algorithm
py.crypto.sha1	Low	A	hashlib.sha1() — weak hash algorithm

Template Injection

Rule ID	Severity	Tier	Description
py.xss.jinja_from_string	Medium	A	jinja2.Template.from_string() — template injection

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Examples

py.deser.pickle_loads — Unsafe deserialization

Vulnerable:

import pickle
data = pickle.loads(request.body)  # Arbitrary code execution

Safe alternative:

import json
data = json.loads(request.body)  # JSON is safe

py.cmdi.subprocess_shell — Shell execution

Vulnerable:

import subprocess
subprocess.call(user_input, shell=True)  # Command injection

Safe alternative:

import subprocess
import shlex
subprocess.call(shlex.split(user_input), shell=False)
# Or better: use an explicit command list
subprocess.call(["ls", "-la", user_dir])

py.deser.yaml_load — Unsafe YAML

Vulnerable:

import yaml
config = yaml.load(user_data)  # Can instantiate arbitrary objects

Safe alternative:

import yaml
config = yaml.safe_load(user_data)  # Only basic Python types

py.sqli.execute_format — SQL concatenation

Vulnerable:

cursor.execute("SELECT * FROM users WHERE id=" + user_id)

Safe alternative:

cursor.execute("SELECT * FROM users WHERE id=?", (user_id,))