Fix Command Injection in TurboGears
Command injection in TurboGears occurs when unsanitized user input from controller arguments is passed to shell-executing functions. In this guide, we'll look at how to move from dangerous shell execution to secure, parameterized process spawning.
The Vulnerable Pattern
from tg import expose import os
class RootController(BaseController): @expose() def index(self, user_input): # CRITICAL: Shell metacharacters in user_input will execute # Example attack: ?user_input=;cat /etc/passwd command = ‘ls -la ’ + user_input data = os.popen(command).read() return dict(output=data)
The Secure Implementation
The exploit vector relies on the system shell (sh/bash) interpreting control characters like ';', '&', or '|'. When using os.popen or subprocess.Popen with shell=True, the input is parsed by the shell, allowing attackers to chain commands. The fix involves using the subprocess module with shell=False (the default) and passing the command and its arguments as a list. This ensures the OS treats the user input as a literal string argument for the specific binary, bypassing the shell's command parser entirely.
from tg import expose, abort import subprocess
class RootController(BaseController): @expose() def index(self, user_input): # FIX: Pass arguments as a list and disable shell execution try: # shell=False is the default and prevents shell interpretation cmd = [‘ls’, ‘-la’, user_input] data = subprocess.check_output(cmd, stderr=subprocess.STDOUT, shell=False) return dict(output=data.decode()) except subprocess.CalledProcessError: abort(400, ‘Command execution failed’) except Exception: abort(500, ‘Internal server error’)
Your TurboGears API
might be exposed to Command Injection
74% of TurboGears apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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